Hydroxypropyl-methylcellulose and Methylcellulose Structured Oils as

an Alternative Low Saturated Fat Stabilizer and Shortening

Replacement for Food Applications

by

Rachel Tanti

A Thesis

presented to

The University of Guelph

In partial fulfillment of requirements

for the degree of

Master of Science

in

Food Science

Guelph, Ontario, Canada

© Rachel Tanti, September, 2015

ABSTRACT

HYDROXYPROPYL-METHYLCELLULOSE AND METHYLCELLULOSE

STRUCTURED OILS AS AN ALTERNATIVE LOW SATURATED FAT STABILIZER

AND SHORTENING REPLACEMENT FOR FOOD APPLICATIONS

Rachel Tanti Advisors:

University of Guelph, 2015 Dr. Shai Barbut

Dr. Alejandro G. Marangoni

The physical properties of freeze dried hydroxypropyl methylcellulose- (HPMC) and

methylcellulose- (MC) structured oil as a stabilizer in peanut butter and a shortening replacement

in cookie creams were investigated. Microstructural analysis revealed morphological differences

between unaltered, freeze dried, and spray dried HPMC, with freeze dried structures showing

highest oil holding capacity. Peanut butters were stabilized with 0.4 to 2.2 wt% HPMC or MC;

significant reduction in oil loss was seen at 0.4 wt%, and no oil loss occurred at 2.2 wt%. As

polymer concentration increased, firmness and adhesiveness increased to match commercial

products. Substitution of shortening for HPMC- and MC-stabilized oil resulted in cookie creams

with lower saturated fat content, reduced oil loss, and increased long-term stability. Shortening

replacement at 50 and 75% of the fat content reduced overall cream stickiness and gumminess,

and showed similar small and large amplitude rheological behaviour as compared to a commercial

benchmark.

iii

ACKNOWLEDGEMENTS

I would like to extend my sincere thanks to my supervisor, Dr. Shai Barbut, for giving me

the opportunity to further myself as a scientist, for sharing his abundant knowledge, and for his

continuous guidance and support. Thank you Dr. Alejandro Marangoni, for your encouragement

and great insight. Working and learning from both of these great minds has been an experience

for which I am extremely grateful.

I would like to thank everyone in the lab and department, who make such a supportive,

friendly and productive work environment, I am lucky to have so many food science friends. To

those that helped me tremendously throughout my research, experiments and writing stages:

Sandy, Fernanda, Andrew, Saeed, Margaret, and anyone else who helped me out one way or

another, thank you.

Thank you to my friends, who have been a great support to me. Finally, I would like to

acknowledge my fam jam: Nomi, Colleenie, Alicia, Joe, Nut, dad, and mom! You have given me

ongoing encouragement, strength, laughter and love throughout my experience here and

everywhere else. Thank you.

iv

TABLE OF CONTENTS

ABSTRACT .................................................................................................................................... ii

ACKNOWLEDGEMENTS ........................................................................................................... iii

TABLE OF CONTENTS ............................................................................................................... iv

LIST OF TABLES ........................................................................................................................ vii

LIST OF FIGURES ..................................................................................................................... viii

CHAPTER 1 Introduction.............................................................................................................. 1

References ................................................................................................................................... 7

CHAPTER 2 Literature Review .................................................................................................... 9

2.1. Oil Structuring Strategies ..................................................................................................... 9

2.1.1. Crystalline Particles ..................................................................................................... 10

2.1.2. Crystalline Fibers ......................................................................................................... 10

2.1.3. Structured Emulsions ................................................................................................... 11

2.1.4. Inorganic Particles ....................................................................................................... 12

2.1.5. Polymeric Strands ........................................................................................................ 13

2.2. Organogels in Food Applications ....................................................................................... 15

2.2.1. Spreads ........................................................................................................................ 15

2.2.2. Cookies ........................................................................................................................ 16

2.2.3. Breads, Cakes, and Pastries ......................................................................................... 17

2.2.4. Cream Fillings and Ice Cream ..................................................................................... 18

2.2.5. Comminuted Meat Products and Cheese ..................................................................... 19

2.3. Peanut Butter ...................................................................................................................... 19

2.3.1. Value and Standard of Identity .................................................................................... 19

2.3.2. Peanut Butter Stabilizers ............................................................................................. 21

2.3.3. Textural Properties of Peanut Butter ........................................................................... 23

2.3.3. Peanut Butter Microstructure ...................................................................................... 26

2.4. Cream Filling...................................................................................................................... 28

2.4.1. Formulation Considerations ........................................................................................ 29

References ................................................................................................................................. 31

CHAPTER 3 Oil stabilization of natural peanut butter using food grade polymers .................... 38

1. Introduction ............................................................................................................................... 39

v

2. Materials and Methods .............................................................................................................. 43

2.1. Sample Preparation ............................................................................................................ 43

2.1.1. Stabilizer Preparation .................................................................................................. 43

2.1.2. Structured oil ............................................................................................................... 44

2.1.3. Peanut butter ................................................................................................................ 44

2.2. Peanut Butter Analysis ....................................................................................................... 45

2.2.1. Total Fat and Protein Content ...................................................................................... 45

2.2.2. Particle Size Distribution ............................................................................................. 45

2.3. Oil Loss .............................................................................................................................. 46

2.3.1. Structured oil ............................................................................................................... 46

2.3.2. Peanut butter ................................................................................................................ 46

2.4. Texture Analysis ................................................................................................................ 46

2.5. Microstructure .................................................................................................................... 47

2.5.1. Light Microscopy ........................................................................................................ 47

2.5.2. Scanning electron microscopy (SEM) ......................................................................... 48

2.5.3. Cryo-SEM .................................................................................................................... 48

2.6. Statistical Analysis ............................................................................................................. 48

3. Results and Discussion ............................................................................................................. 49

3.1. Peanut butter fat, protein and particle size analysis ........................................................... 49

3.2. Oil Loss .............................................................................................................................. 51

3.2.1. Structured oil ............................................................................................................... 51

3.2.2. Peanut butter ................................................................................................................ 52

3.3. Texture ............................................................................................................................... 55

3.4. Microstructure .................................................................................................................... 59

3.4.1. Additive and Structured oil.......................................................................................... 59

3.4.2. Peanut butter ................................................................................................................ 62

4. Conclusions ........................................................................................................................... 64

Acknowledgements ................................................................................................................... 65

References ................................................................................................................................. 65

CHAPTER 4 Hydroxypropyl methylcellulose and methylcellulose structured oil as a

replacement for shortening in sandwich cookie creams ............................................................... 69

vi

ABSTRACT .................................................................................................................................. 69

1. Introduction ............................................................................................................................... 70

2. Materials and Methods .............................................................................................................. 73

2.1. Structured Oil Preparation .................................................................................................. 73

2.2. Cookie Cream Preparation ................................................................................................. 73

2.3. Total Fat and Fatty Acid Composition ............................................................................... 74

2.4. Oil Loss .............................................................................................................................. 75

2.5. Texture Profile Analysis (TPA) ......................................................................................... 76

2.6. Small and Large Amplitude Oscillatory Shear Rheology .................................................. 76

2.6.1. Small Amplitude Oscillatory Shear Rheology ............................................................ 76

2.6.2. Large Amplitude Oscillatory Shear Stress (LAOStress) Rheology ............................ 77

2.8. Statistical Analysis ............................................................................................................. 77

3. Results and Discussion ............................................................................................................. 77

3.1. Total Fat and Fatty Acid Content ....................................................................................... 77

3.2. Oil Loss .......................................................................................................................... 78

3.3. Texture ............................................................................................................................... 80

3.4. Small Amplitude Oscillatory Shear Rheological Behaviour.............................................. 82

2.5. Large Amplitude Oscillatory Shear Stress Behaviour ....................................................... 86

4. Conclusions ............................................................................................................................... 90

Acknowledgements ....................................................................................................................... 91

CHAPTER 5 Conclusions and Future Directions ......................................................................... 94

vii

LIST OF TABLES

CHAPTER 3

Table 1 Total fat content, available oil and crude protein for the industry standard brands (St-1

& St-2) (stabilized with hydrogenated vegetable oil) and natural peanut butter brands

(Nat-A & Nat-B) (base material for treatments)…………………………...…………… 50

Table 2 Time until oil loss occurred for natural peanut butter stabilized with 0.4 to 1.0 and

2.2% hydroxypropyl methylcellulose (HPMC)/methylcellulose (MC) powder (-C) and

freeze dried (-FD) material…………………………………………….…………..…… 55

Table 3 The effect of adding 2.2% hydroxypropyl methylcellulose (HPMC) that was prepared

by spray drying (SD) or the control powder (C) to natural peanut butter brands A and B

on textural parameters………………………………………..…………………………. 59

CHAPTER 4

Table 1 Composition of experimental cookie creams containing hydroxypropyl

methylcellulose (HPMC) and methylcellulose (MC) structured oil at different substitution

levels (0, 50, 75, and 100%)……………………………………………………….……. 74

Table 2 Fatty acid composition and total fat content of commercial sandwich cookie creams, a

commercial shortening and canola oil. All values are reported in wt%………………... 78

Table 3 Fitted parameters of the fast and slow oil loss components (Y, component percent; k,

rate constant) obtained using a two-phase association model. Commercial standard (CS1),

shortening control (Ctrl), and sandwich cookie cream treatments made with increasing

shortening replacement (50, 75, 100 wt%) with hydroxypropyl methylcellulose (HPMC),

and methylcellulose (MC) structured canola oil……………….……………………….. 80

Table 4 Texture profile analysis parameters of commercial standard (CS) sandwich cookie

creams (1 to 6)………………………………………………………...………………… 81

Table 5 Effect of 50, 75, and 100% shortening replacement with hydroxypropyl

methylcellulose (HPMC), and methylcellulose (MC) structured canola oil on texture

profile anlysis parameters of sandwich cookie creams…………………...…………….. 82

viii

LIST OF FIGURES

CHAPTER 3

Figure 1. Characteristic force-deformation curve of a stabilized peanut butter samples. Texture

parameters interpreted include firmness (A), stretch (B-D), adhesion (C), work of

penetration (1), adhesiveness (2)………………………………..……………………… 47

Figure 2. Particle size distribution of industry standard peanut butter brands- 1 and 2 (stabilized

with hydrogenated vegetable oil ) (a) and natural peanut butter brands A and B (base

material for treatments) (b)……………… …………………………………………….. 51

Figure 3. Oil loss curves of freeze dried hydroxypropyl methylcellulose (HPMC) and

methylcellulose (MC) in peanut oil. N=3, Means±standard error……………...………. 52

Figure 4. Effect of hydroxypropyl methylcellulose and methylcellulose control powder (HPMC-

C/MC-C) or hydroxypropyl methylcellulose and methylcellulose freeze dried material

(HPMC-FD/MC-FD) to natural peanut butter brands A and B on percent oil loss. The

dotted lines in (b) show the value of the commercial standards 1 and 2 stabilized with

hydrogenated vegetable oil…………………………………………………………...… 54

Figure 5. The effect of adding hydroxypropyl methylcellulose and methylcellulose powder (HP-

C/MC-C) or hydroxypropyl methylcellulose and methylcellulose freeze dried material

(HP-FD/MC-FD) to natural peanut butter brands A and B on textural parameters. The

dotted lines show the value of the commercial standard A and B stabilized with

hydrogenated vegetable oil…………………………………………………………...… 58

Figure 6. SEM micrographs of hydroxypropyl methylcellulose (HPMC): control powder (a),

spray dried HPMC (b), freeze dried HPMC xerogel (c) and sheared freeze dried HPMC

xerogel (d)……………………………..…………………………..……………………. 61

Figure 7. Light micrographs of 3% hydroxypropyl methylcellulose (a-b) and methylcellulose (c-

d) in peanut oil. Low magnification images (a,c), high magnification of isolated polymer

sheets (b,d)…………………………………………………...…………………………. 62

ix

Figure 8. Cryo-scanning electron microscopy images of (a) natural peanut butter brand B, and

(b) peanut butter brand B with 1.5% wt. freeze dried hydroxylpropyl methylcellulose

added………………………………………………………………………………….… 63

Figure 9. Light microscopy image of protein bodies (p), cell wall fragments (w), and starch

granules (s) dispersed in the oil matrix of (a) natural peanut butter Brand A, (b)

hydrogenated commercial standard A, (c) natural peanut butter brand A with 1.5% freeze

dried HPMC, (d) natural peanut butter brand A with 1.5% freeze dried MC…………... 64

CHAPTER 4

Figure 1. Oil loss curves for (a) commercial standard (CS1, ) and shortening control (Ctrl, )

sandwich cookie creams compared to creams made with increasing shortening

replacement from (b) hydroxypropyl methylcellulose (HPMC), and (c) methylcellulose

(MC) structured canola oil (50, ; 75, ; 100, wt%)……………………………….. 79

Figure 2. Stress sweeps for commercial standard (CS) sandwich cookie creams performed at a

constant 25 °C. CS1 (a), CS2 (b), CS3 (c), CS4 (d), CS5 (e), CS6 (f)…………………. 84

Figure 3. Stress sweeps for sandwich cookie cream samples made with increasing shortening

replacement (50 and 75) with hydroxypropyl methylcellulose (HPMC), and

methylcellulose (MC) structured canola oil performed at a constant 25°C. Commercial

standard (a), icing shortening control (b), 50 HPMC (c), 50 MC (d), 75 HPMC (e), 75

MC (f)…………………………………………………………………………………... 86

Figure 4. Lissajous plots for commercial standard (CS) sandwich cookie creams CS1(a), CS2 (b),

CS3 (c), CS4 (d), CS5 (e), CS6 (f), performed at a constant 25°C, at stress amplitudes of

551, 1510, 2013, 2684 Pa (97, 150, 201, 551 Pa for CS6)…………………………...… 88

Figure 5. Lissajous plots for sandwich cookie creams made with increasing shortening

replacement (50 and 75%) with hydroxypropyl methylcellulose (HPMC), and

methylcellulose (MC) structured canola oil performed at a constant 25°C, at stress

amplitudes of 551, 1510, 2013, 2684 Pa. Samples shown are the commercial standard

(a), icing shortening control (b), 50 HPMC (c), 50 MC (d), 75 HPMC (e), 75 MC (f)… 90

1

CHAPTER 1

Introduction

The health effects of fat consumption and the associated risk of cardiovascular disease

(CVD) has been a controversial area of research over the past several decades (Ascherio et al.,

1996; McGee, Reed, Yano, Kagan, & Tillotson, 1984). The health controversy surrounding

saturated fat can be traced back to an epidemiological study conducted by Keys (1970),

commonly known as the Seven Countries Study. Keys (1970) showed that the percentage of

caloric intake from saturated fat was positively associated with coronary related deaths, whereas

a negative association was found from monounsaturated fat consumption. Since this time, many

concerns regarding the validity of the Seven Countries Study have been raised (Reiser, 1973), as

well as multiple observational and experimental trials have since shown contradictory results

regarding the deleterious health effects of saturated fat consumption (Shekelle et al., 1981;

McGee, Reed, Yano, Kagan, & Tillotson, 1984; Ascherio et al., 1996; Hu, Manson, & Willett.,

2001). Some studies have shown positive associations between consumption of saturated fat and

risk of CVD (Hu , Manson, & Willett, 2001; McGee, Reed, Yano, Kagan, & Tillotson, 1984),

whereas others have not (Ascherio et al., 1996; Shekelle et al., 1981); a single study has shown

an inverse association between consumption of polyunsaturated fat and CVD (Shekelle et al.,

1981), whereas again, several others have not (Ascherio et al., 1996; Hu, Manson, & Willett,

2001). The aforementioned collection of studies on this matter indicates that there is no

consensus in literature regarding the consumption of saturated fat and an increased risk of CVD.

However, studies regarding the negative health effects of trans fat consumption is more

conclusive.

2

The major sources of dietary fat have changed within the past century (Blasbalg, Hibbeln,

Ramsden, Majchrzak, & Rawlings, 2011), with the use of butter and lard being slowly replaced

by inexpensive and more versatile plant-based oils and shortenings. With the introduction of

mechanization, vegetable oils were becoming less expensive than animal fat sources. As a result,

researchers had been putting forth tremendous effort towards changing the characteristics of fats,

specifically changing the melting point of inexpensive oils to manufacture margarines and

shortenings to act as lard and butter substitutes (Schleifer, 2012). In certain cases, animal derived

shortenings, such as lard and compound lard (vegetable oil mixed with lard), became perceived

as being unhealthy, unhygienic and adulterated due to their association with the unsavoury

conditions in the meat-packing industry and popular marketing of all-vegetable shortenings

(Schleifer, 2012).

It was found that oils could be stabilized as well as be made more functional for inclusion

into food products by turning liquid oil into a solid fat via hydrogenation. Fully-hydrogenated

oils yielded brittle fats, however, partial hydrogenation created semi-solid fats which could be

used for many food applications. This was achieved by varying temperature, pressure, agitation,

and catalyst concentration of the hydrogenation reaction, thereby creating a number of different

hydrogenated fats with tailored characteristics in structure, texture, lubrication, tenderness, and

aeration for the intended food product (Schleifer, 2012). It was thought that since these

hydrogenated fats came from healthful vegetable oils, that originally contained low saturated fat

content, they were a healthy alternative to animal derived fats. Hydrogenated oils became

ubiquitous in the food industry, with the replacement of butter and lard with margarines and

shortenings in cakes, cookies, chips, breads, icings, fillings, etc. However, partially hydrogenated

oils (PHOs) contain trans fats, which have now been identified to cause negative health effects

3

(AHA, 2014; FDA, 2015; Hu et al., 2001). It is important to note that trans fats also naturally

occur in certain foods, such as meats and dairy products. These ruminant trans fats are present in

very low amounts, and have not been conclusively associated with the negative health effects of

industrial-produced trans fats (Brouwer, Wanders, & Katan, 2010; Jakobsen, Overvad,

Dyerberg, & Heitmann, 2008).

The reduction of saturated fat in the diet has been a long standing recommendation. The

first dietary guidelines in the United States were published by the American Heart Association in

1957, and later the U.S Senate in 1977. In regards to fat consumption, they recommended overall

fat consumption should account for a total of 30-40% total caloric intake with a reduction of

saturated fat consumption to upwards of 10% total caloric intake and balance the remainder with

poly and monounsaturated fat sources (Kritchevsky, 1998). Recently, the generally recognized as

safe (GRAS) status of PHOs was removed by the US Food and Drug Administration (FDA) with

a three year compliance period (FDA, 2015). Scientific evidence has shown that the consumption

of trans fat from PHOs is associated with increased levels of low density lipoprotein (LDL)

cholesterol, decreased levels of high density lipoprotein (HDL) cholesterol, and increased levels

of plasma triglyceride. All three factors are well defined risk markers for CVD and promote

insulin resistance in humans which leads to the onset of pre- and type 2 diabetes (Hu, Manson, &

Willett., 2001; AHA, 2014; FDA, 2015).

In 2003, the FDA mandated that all packaged food manufacturers must label trans fat

content on their products (FDA, 2003). In 2007, Heath Canada stated that trans fats should be

limited to 5% of the total fat content in the food product and that spreadable margarines should

be limited to 2% total fat content (Health Canada, 2009). The Minister of Health called on the

food industry to comply with these recommendations within 2 years and began a monitoring

4

program to track the trans fat content in specific food products. In 2009, the World Health

Organization (WHO) deemed trans fat produced by partial hydrogenation of fats and oils to be

considered an industrial food additive that demonstrated no health benefits and a clear risk to

human health, and recommended trans fat should consist of less than 1% of an individuals’ daily

caloric intake (Uauy et al., 2009).

Removing trans fat and PHOs from processed foods has already been undertaken by

many companies, however trans fat can still be abundantly found in products such as frozen

packaged baked desserts, baked goods, coffee creamers/whiteners, spreads, fried foods,

refrigerated doughs, vegetable shortening, etc. (Health Canada, 2009). Removal of saturated fats

from animal sources has also been undertaken with the introduction of low-fat milk and meat

products, however much of the time, these saturated fats are replaced with carbohydrates. This

strategy of saturated fat replacement, however, has been a cause of concern because low-fat,

high-carbohydrate diets are associated with a different set of health issues including

dyslipidemia, a component of metabolic syndrome (Forsythe et al., 2008; USDA, 2015; Volek,

Fernandez, Feinman, & Phinney, 2008).

Many food products are formulated with high amounts of saturated fat and/or trans fat

because they contribute to the product’s flavour, texture, mouthfeel, and functionality (Co &

Marangoni, 2012). Research on how to replace these fats in food products without negatively

affecting the organoleptic properties has been a topic of concern for the food industry and

researchers alike. From an industrial perspective, a ‘drop-in replacement’ or an ingredient that is

completely interchangeable in a process is of the highest value. Ideally, changes to a product

recipe should have minimal effects on product processing and the final properties of the product.

Any changes to how a product must be processed upon the addition of the replacement

5

ingredient can impact the quality of the final product and may incur losses, financial or other.

Researchers must then be able to develop a suitable replacement that is both functionally and

economically feasible. It is also important to consider other factors when seeking replacements

for fats and oils, such as environmental sustainability, which is why the use of tropical oils, such

as palm oil, is of concern (Uauy et al., 2009).

Recently, the use of edible organogels, or oleogels, have become a popular strategy to

replace saturated fats in a variety of food products (Marangoni & Garti, 2011; Rogers et al.,

2014). Traditionally, hardstock fats are structured with triacylglcerides (TAGs), which provide a

hierarchical crystalline structure which binds and traps oil that in turn provides structure and

desirable functionality to numerous food products such as cheese, butter, lard, etc. (Acevedo &

Marangoni, 2010; Zetzl & Marangoni 2011). It is within these TAG structuring agents that trans

and saturated fatty acids are present. Organogelation is a novel strategy that involves adding a

gelator or a structuring agent to liquid oils which subsequently forms a network that traps oil and

imparts a solid-like character that is analogous to a hardstock fat. Many structuring agents have

been identified that can be added or prepared with oil in order to mimic the functionality of

hardstock fats that are both free of trans and have reduced saturated fat content. Direct

approaches for obtaining organogels include structuring agents such as monoacylglycerides

(MAGs), ricinelaidic acid, 12-hydoxystearic acid (12-HSA), ethylcellulose, cerimides, and wax

esters (Marangoni & Garti, 2011). Another recent method found is the use of indirect structuring

agents which include foam and emulsion templates made from modified polysaccharides and

proteins to form functional structured oils (Patel, 2015).

One of the benefits of organogels is their high degree of versatility. For example, multiple

different oils, structuring agents and mixtures of the two can be used to replace trans and

6

saturated fats. These combinations result in structured oils with different functionalities which

then can be applied to different food products that have specific fat requirements. Multiple

studies have been conducted in order to understand how these structured oils behave and effect

the properties of different food applications including frankfurters (Zetzl, Marangoni, & Barbut,

2012), ice cream (Zulim, Botega, Marangoni, Smith, & Goff, 2013), chocolate (Rogers et al.,

2014), cookies (Yilmaz & Ögütcü, 2015), and cream filling (Hughes, Marangoni, Wright,

Rogers, & Rush, 2009). The understanding of food systems has become increasingly important

in order to design its functional components, which in this case, is its fat content. As a result,

further research needs to be examined in individual food systems in order to understand the

effectiveness of replacing saturated and trans fat with structured oils.

There are two objectives of this study. First, to examine the oil binding abilities of HPMC

and MC to stabilize oil when prepared as spray dried powder and freeze-dried porous foams

sheared into sheets. These preparation methods will be compared to the original unaltered

HPMC/MC powder. This will give an insight into whether morphology plays a role in oil

stability as well as chemical character. Secondly, the potential of these HPMC and MC

structured oils in two food applications will be investigated including a stabilizer for peanut

butter and shortening replacement in a cookie filling. The hypotheses of this study are as follows:

1. The oil binding mechanism of HPMC and MC is mainly physical and is effected by

stabilizer morphology

2. Peanut butter stabilized with freeze dried material will be a more effective stabilizer than

spray dried material followed by the unaltered control powder

3. HPMC and MC will be a suitable partial shortening replacement in icing

7

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fatty acid partitioning, and metabolic syndrome. Progress in Lipid Research, 47(5), 307–18.

Zetzl, A. K., Marangoni, A. G., & Barbut, S. (2012). Mechanical properties of ethylcellulose

oleogels and their potential for saturated fat reduction in frankfurters. Food & Function,

3(3), 327–37.

Zulim Botega, D. C., Marangoni, A. G., Smith, A. K., & Goff, H. D. (2013). The potential

application of rice bran wax oleogel to replace solid fat and enhance unsaturated fat content

in ice cream. Journal of Food Science, 78(9), 1334–1339.

9

CHAPTER 2

Literature Review

2.1. Oil Structuring Strategies

Edible fats are composed of triacylglycerol molecules (TAGs). These TAGs consist of a

glycerol back bone with three fatty acid chains attached by ester linkages. The chemical nature of

the fatty acids gives solid-like or liquid-like character to a particular fat at room temperature, and

the interaction between crystalline TAG molecules is what traditionally structures hardstock fat

(Acevedo & Marangoni, 2010). Typically, a bulk fat containing a large proportion of long-chain

fatty acids, with high degree of saturation, results in a fat with a higher melting point that is solid

at room temperature. Whereas, fats containing a high amount of short-chain fatty acids, with a

high degree of unsaturation, results in a fat that has a lower melting point and is liquid at room

temperature. This is the main difference between fats and oils, and what dictates the suitability of

a fat in a particular food application. Semi-solid fats provide a variety of characteristics to

different baked goods that oils cannot. For example, solid fats can trap small air bubbles that stay

in cake batters longer, producing more reliably fluffy cakes. Solid fats can also keep dough

layers apart in pastries resulting in increased volume or lift, whereas, using an oil for these

applications would result in lower volume cakes and dough layers that adhere together and leak

oil (Schleifer, 2012).

Organogelation, or the gelling of oils, offers an alternative method of structuring lipids

for use in food products that would otherwise use high amounts of saturated and/or trans fats.

Another application of organogels in food systems is inhibiting oil migration due to

organogelation increasing the viscosity of the oil phase, therefore reducing its mobility and oil

leakage (Co & Marangoni, 2012). Many strategies of oil structuring have been reported using

10

multiple different structuring agents that are food-grade, economically feasible, and are able to

impart desirable physical properties at low concentrations (Co & Marangoni, 2012). These

structuring agents can be loosely defined under the following categories: crystalline particles,

crystalline fibers, structured emulsions, polymeric strands (Marangoni & Garti, 2011), and more

recently inorganic particles (Patel, 2015). The following section will give a brief summary of the

aforementioned novel oil structuring methods.

2.1.1. Crystalline Particles

Apart from the traditional TAG structuring, monoacylglycerols (MAGs), diacylglycerols

(DAGs), ceramides, and sorbitan monostearate have been shown to be able to self-assemble to

structure oil (Rogers, 2009). MAGs and DAGs are more polar than TAGs as a result of their free

hydroxyl groups on the glycerol backbone. This gives them the ability to efficiently structure oil

at concentrations of 10 wt% (Marangoni et al., 2007). Plant based waxes are also capable of

structuring oil at low concentrations (1-4 wt%) by forming crystalline particles that aggregate

and form a network that entraps oil (Marangoni & Garti, 2011). Some major sources of wax that

have been studied include rice bran wax (Dassanayake, Kodali, Ueno, & Sato, 2009), sunflower

wax (Hwang, Kim, Singh, Winkler-Moser, & Liu, 2012), candelilla wax (Toro-Vazquez et al.,

2007), carnauba wax (Rocha et al., 2013), shellac wax (Patel, Schatteman, De Vos, Lesaffer, &

Dewettinck, 2013), beeswax (Öğütcü, Arifoğlu, & Yılmaz, 2015),and sugarcane wax (Rocha et

al., 2013).

2.1.2. Crystalline Fibers

Oil structuring can be achieved by self-assembled fibrillar networks (SAFIN) of low

molecular weight gelators (LMOG), for example 12-hydrozystearic acid (12-HSA), ricinelaidic

acid, and phytosterols with orzanol (Marangoni & Garti, 2011). These gelators are capable of

11

forming helical and twisted crystalline ribbons, hundreds of micrometers long, which immobilize

oil.

2.1.3. Structured Emulsions

One of the first oil gels that demonstrated viability for the use in food applications was a

structured oil-in-water emulsion consisting of oil encapsulated in multilamellar crystalline

monoglyeride vesicles (Marangoni et al., 2007). The properties of MAG gels were exploited to

create a simple and highly stable oil-in-water emulsion with 27 to 70% (v/v) water, 66 to 27%

(v/v) oil, zero trans, and low saturated fat content (Marangoni et al., 2007). These structured

emulsions consisted of oil droplets stabilized by hydrated self-assembling MAGs, which upon

cooling, crystallized to form an alpha gel with high amounts of water entrapped between stacked

bilayers which, over time, eventually transformed into an anhydrous crystalline phase or coagel

(Marangoni et al., 2007). The resultant structured emulsion exhibits a fat-like appearance with

highly versatile shortening functionality and is commercially available today as CoasunTM

(Coasun, 2015).

Another method of creating structured emulsions was achieved by forming an organogel

using shellac (Patel, Schatteman, De Vos, et al., 2013) or beeswax (Öğütcü et al., 2015) in oil,

and incorporating water into the molten organogel continuous phase in either the presence or

absence of varying amounts of emulsifiers (e.g., Tween20, Tween80) and hydrocolloids (e.g.,

xanthan gum, XG). The water is dispersed in the molten organogel and subsequently cooled to

entrap water droplets in the resultant crystalline organogel network. The shellac emulsions,

which were prepared in the absence of any emulsifiers, consisted of 20 wt% water with either

1.6, 3.2, or 4.8 wt% shellac (Patel, Schatteman, De Vos, et al., 2013). This emulsion is stabilized

by a combination of physical entrapment and steric stabilization as shellac both imparts structure

12

to the continuous oil phase and accumulates at the water-oil interface, which prevents

coalescence and phase separation (Patel et al., 2013). The beeswax structured emulsions

contained 3.75-4.50 wt% beeswax in the final emulsion and required the presence of emulsifiers

and XG to remain stable (Öğütcü et al., 2015). It was speculated that Tween 20 or Tween 80

incorporation increased the hydrophilic-lipophilic balance (HLB) value making the mixture more

suitable for a water-in-oil emulsion. The addition of XG increased the viscosity of the water

phase and decreased the sample melting point.

Alternatively, the addition of various food-grade hydrocolloids has been used to create

structured emulsions called high internal phase emulsions (HIPE) (Patel, Rodriguez, Lesaffer, &

Dewettinck, 2014). Galactomannans show synergistic interactions with carrageenan, XG, and

locust bean gum that are capable of forming gels at low polymer concentrations. These

hydrocolloid mixtures, in water, can be finely dispersed in an oil continuous phase at >70 C and

subsequently cooled to produce a high phase volume of closely packed gelled droplets that

physically entraps oil and exhibits gel-like behaviour (Patel, Rodriguez, Lesaffer, & Dewettinck,

2014).

2.1.4. Inorganic Particles

Hydrophilic fumed silica was able to structure sunflower oil to produce viscoelastic gels

at concentrations of 10 and 15 wt% when silica particles were dispersed uniformly in oil under

high shear (Patel, Mankoč, Bin Sintang, Lesaffer, & Dewettinck, 2015). At lower concentrations

(2.5 and 5 wt%), the samples were viscous sols with negligible yield stresses. This was attributed

to the highly concentrated samples having a higher degree of particle-particle interactions

leading to a stronger fractal-like network formation which entrapped oil (Patel et al., 2015). In

addition, a weak hydrogel containing locust bean gum and carrageenan could be mixed with the

13

15 wt% silica organogel to produce a bigel, which showed a higher gel strength than either

component in isolation (Patel et al., 2015).

2.1.5. Polymeric Strands

The only known direct polymeric organogelator and one that has shown great potential

for use in food applications is ethylcellulose (EC). EC is a derivative of cellulose chemically

modified by substituting the hydroxyl groups on the cellulose backbone with ethyoxy groups.

This renders EC soluble in oil above its glass transition temperature (Tg ~135 C) and upon

cooling forms a three-dimensional entangled polymer network and a resultant gel. The

functionality, microstructure, and processing conditions of these gels have been extensively

studied (Davidovich-Pinhas, Gravelle, Barbut, & Marangoni, 2015; Gravelle, Barbut, Quinton, &

Marangoni, 2014; Zetzl, Marangoni, & Barbut, 2012). Other food-grade polymers have been

used to structured oils via an indirect methodology involving creating polymeric templated

scaffoldings which are also capable of physically entrapping oil.

One of these indirect methods is referred to as emulsion templating, which is a high

energy throughput, multi-phased approach involving: 1) dissolving a combination of polymers in

water, 2) emulsifying oil to form a stable oil-in-water emulsion, 3) evaporating off the water

phase (e.g., oven drying) and finally, 4) shearing of the dried emulsion to obtain clusters of

tightly packed oil droplets in an oil continuous phase (Patel, Cludts, Bin Sintang, et al., 2014).

XG was used as a thickening agent and either hydroxypropyl methylcellulose (HPMC) or

methylcellulose (MC) were used as emulsifying agents (Patel et al., 2015; Patel, Cludts, Bin

Sintang, et al., 2014). Emulsions prepared with HPMC or MC alone resulted in coalescence and

oil leaking upon drying. XG used in isolation could not emulsify, as it is non surface active,

whereas, when incorporated in combination with HPMC/MC a more uniform oil droplet size

14

distribution and stable dried emulsion is achieved (Patel, Cludts, Bin Sintang, et al., 2014). In

another study, it was found that the XG could also be used in combination with gelatin (a

protein) to produce similar structured oils where an increase of polymer concentration at the oil-

water interface resulted in increased gel strength (Patel et al., 2015). The microstructure of these

structured oils shows distinct tightly packed oil droplets resembling that of a HIPE (Patel, Cludts,

Bin Sintang, et al., 2014).

An alternative indirect method of oil structuring involved adsorbing oil to a HPMC

scaffold, referred to as foam-templated organogels (Patel, Schatteman, Lesaffer, & Dewettinck,

2013). In this work, an aqueous solution of HPMC was foamed mechanically to incorporated air

and freeze dried to create a porous structure which is able to adsorb a high amount of oil;

however, since freeze drying creates an open celled structure, oil will be released under

compression. To prevent this, the oil saturated foams were sheared to disperse the polymer sheets

and trap the oil (Patel, Schatteman, Lesaffer, & Dewettinck., 2013). This templating concept has

also been used previously to partially (60%) and fully substitute pork backfat content in

fermented sausages by adsorbing extra-virgin olive oil to a whey protein based crumb and white

pan bread (Alessandro et al., 2009). Alessandro et al. found no significant difference in weight

losses of the oil soaked whey protein based crumb, white pan bread, and full fat control products.

In addition, taste, colour and odour characteristics of the 60% replacement with oil soaked whey

protein crumb were comparable to the commercial product, however, long term stability was not

examined. Another application for this templating concept is the use of cellulose based freeze-

dried foams as oil absorbents for cleaning oil spills in water (Korhonen, Kettunen, Ras, & Ikkala,

2011). The freeze-dried foams used for oil spill applications, typically are not food grade, which

makes HPMC foams unique and useful for food applications. HPMC and MC have been used in

15

the food, cosmetic, and pharmaceutical industries for decades and both have been granted a

GRAS status by the US FDA. HPMC and MC are well known for their ability to create gels in

aqueous solutions, but literature is limited on their use in oil based systems. The potential of

freeze dried HPMC and MC as a stabilizer and HPMC- and MC-structured oil as a shortening

replacement in two food applications are the main focus of this thesis.

2.2. Organogels in Food Applications

Previous works on organogels has been predominantly focused on understanding

fundamental properties including microstructure, polymorphism, rheological behaviour, etc. (Co

& Marangoni, 2012; Marangoni & Garti, 2011). This understanding is critical to applying

organogels to food systems as the behaviour of traditional fats need to be mimicked in order to

impart similar if not equal functionality in the final food product. In addition, “drop-in

ingredient” replacement is highly preferred in the food industry to avoid incurred costs. The

desired functional characteristics of the fat content is variable depending of the specifications of

the food application. Replacing highly saturated hard stock fats with liquid oil often causes

increased oil migration resulting in oil leakage and other quality defects. In response to these

problems, an increasing amount of research has focused on exploring the potential use of various

types of organogels in a wide range of food applications. The following is an overview of

organogels used in food applications.

2.2.1. Spreads

Plant wax in soybean oil organogels were used for margarine production, including

candelilla wax (CW), rice bran wax (RBX), and sunflower wax (SFX). It was found that

although CW and RBW are able to form stable organogels, in a margarine formulation CW

16

phase separated and RBW had low firmness; however, SFX was able to form the most

desirable margarine characteristics of the 3 waxes studied (Hwang et al., 2013).

Margarines made using carnauba wax and monoglycerides in virgin olive oil at 3, 7, and 10

wt% concentration levels were studied, all samples, in particular the 7% monoglyceride

sample, resembled the textural and thermal properties of a commercial margarine (Öğütcü

& Yilmaz, 2014).

Shellac organogels were able to fully replace a commercial hydrogenated vegetable oil

stabilizer, partially replace (~27%) palm oil in a chocolate paste, and create an emulsifier-

free margarine with up to 60 wt% water incorporation (Patel, Rajarethinem, et al., 2014).

Margarines made using virgin olive oil organogels containing 5 wt% of beeswax or

sunflower wax demonstrated consumer hedonic liking scores of appearance, odour, flavour

and spreadability above neutrality, demonstrating consumer acceptability of these

margarine replacements (Yılmaz & Öğütcü, 2015a).

2.2.2. Cookies

Structured MAG gels, or CoasunTM was used as an all purpose shortening replacement in

cookies. Traditional all purpose shortening had superior shortening functionality compared

to MAG gels, however, incorporation of the unstructured components of the emulsion

resulted in lower cookie dough firmness and increased spread when compared to its

structured emulsion counterpart (Goldstein & Seetharaman, 2011). Therefore, the

structured emulsion maintained similar dough firmness to the all purpose shortening

dough, indicating that the structured emulsion had a greater ability to act as a structural

component in the cookie dough (Goldstein & Seetharaman, 2011).

17

The ability of MAG gels to act similar to a shortening, such as development time and

prevention of gluten aggregation was demonstrated (Huschka, Challacombe, Marangoni, &

Seetharaman, 2011). These characteristics are beneficial for baked products that do not rely

on gluten network formation for structure, for example, cookies, pie crusts, and pastries.

Traditional shortening was replaced with MAG gel, modified with added 3 to 5 wt% EC

(Stortz, Zetzl, Barbut, Cattaruzza, & Marangoni, 2012). Oil loss was monitored at 37°C

using filter papers to promote oil loss; it was found that cookies made with added EC

resulted in lower oil loss overtime than the structured emulsion.

A standard cookie mixture was used to compare cookies containing approximately 24% fat

content from organogels prepared with 5 wt% SFX and BW in hazelnut oil and a

commercial bakery shortening (Yılmaz & Öğütcü, 2015b). Cookies prepared with

organogels had a lower aeration (indicated by higher diameter: thickness ratio), lower

hardness, higher factorability and equal or higher positive sensory attribute scores than the

cookies prepared with commercial bakery shortening. Therefore, cookies prepared with

wax organogels can be considered to exhibit good sensory quality. This was supported by

consumer hedonic liking data, which indicated that the organogel cookies were preferred

and better accepted than the control cookies (Yılmaz & Öğütcü, 2015b).

Candelilla wax (3 and 6 wt%), canola oil organogels resulted in cookies that had more

spread upon baking, and lower snapping force contributing to softer eating characteristics

than shortening control cookies (Jang, Bae, Hwang, Lee, & Lee, 2015).

2.2.3. Breads, Cakes, and Pastries

MAG organogels were prepared with sunflower oil and were used in sweet bread

(Calligaris, Manzocco, Valoppi, & Nicoli, 2013). Incorporation of MAG organogel

18

resulted in an inhomogeneous lipid distribution in the dough, contributing to low leavening

and firmer structure than a palm oil control.

An emulsion-templated structured oil was made with MC and xanthan gum as a

replacement of traditional shortening in cake batters (Patel, Cludts, Sintang, Lesaffer, &

Dewettinck, 2014). It was found that the batter properties and cake attributes of the

structured oil were comparable to commercial shortenings and showed significant

difference from liquid oil controls (Patel, Cludts, Sintang, et al., 2014).

Shellac wax based emulsions were used as a cake margarine replacement in a basic sponge

cake recipe. It was found that though the shellac emulsion batter properties were not

comparable to the control in terms of density and flow behaviour, the resultant baked cakes

showed mostly comparable textural and sensorial properties (Patel, Rajarethinem, et al.,

2014).

2.2.4. Cream Fillings and Ice Cream

A model cream was prepared using a mix of 60% organogel or oil and 40% intersterified

hydrogenated palm oil (Stortz et al., 2012). The organogel was prepared with 6% EC and

2% sorbitan monostearate with either canola or high oleic sunflower oil (HOSO). An oil

binding test conducted at 20°C using filter papers to promote oil loss showed that creams

made with canola oil and HOSO organogel had very low oil loss compared to creams made

with oil, demonstrating organogelation is an effective way to slow if not prevent oil

migration in cream fillings.

A standard ice cream mix was prepared using a 10% RBX in HOSO organogel to replace

the solid fat content traditionally used in ice creams such as milk fat, or non-dairy sources

such as palm kernel oil, palm oil, coconut oil, or hydrogenated oil (Zulim Botega,

19

Marangoni, Smith, & Goff, 2013). The RBX organogel was successfully emulsified in the

ice cream mix and resulted in characteristics similar to that of crystallized fat droplets than

of liquid oil. However, sufficient structure was not developed to cause a delay in structural

collapse during meltdown (Zulim Botega et al., 2013).

2.2.5. Comminuted Meat Products and Cheese

Replacement of saturated fat with vegetable oil in comminuted meat products, such as

frankfurters, resulted in products that were nearly 3x chewier and had an unacceptable

rubbery texture (Youssef & Barbut, 2010; Zetzl et al., 2012). Frankfurters made with

organogels of 10% EC in oil were not significantly different in hardness or chewiness to

the beef fat controls (Stortz et al., 2012; Zetzl et al., 2012). Pork fat in breakfast sausages

was also replaced with EC organogels (~20% of the product); it was found the textural

qualities of the pork fat control could be matched (Wood, 2013).

Organogels comprised of a mixture of RBX, EC and vegetable oil were used in a cream

cheese product giving comparable spreadability, hardness and had an approximate 25%

reduction in total fat content than the full-fat control product (Limbaugh, 2015). Similarly,

a mixture of organogelators in soybean oil was used to make a processed cheese product

(Huang, 2015).

2.3. Peanut Butter

2.3.1. Value and Standard of Identity

The popularization of peanut butter in North America can be dated back to 1896, when

the U.S. Patent for a “nut butter” made from peanuts or almonds was issued (Shurtleff & Aoyagi,

2015). By 1914, at least 21 different brands of peanut butter were on the market in the United

States (Shurtleff & Aoyagi, 2015). In 2014, the value of nut and seed spreads in the US was

20

approximately $2 billion USD which accounts for about half the commercial value of the spreads

commodity, which also includes chocolate spread, honey, jams and preserves and yeast based

spreads (Euromonitor International, 2014b). The value of nut and seed spreads has increased by

13.5% in the past 5 years, largely due to the increase in diversity of products like niche spreads,

such as almond butter, cashew butter, sunflower seed butter, sesame seed paste and several other

nut and seed spreads currently available. These products have been shown to have healthy lipid

profiles and are gaining in popularity due to their compliance with the current health and

wellness trend among consumers (Euromonitor International 2014; Gorrepati et al. 2014). Peanut

butter itself has a very mature market position, but companies continue to reinvent and brand this

product with different flavours and textures, for example, new ‘whipped peanut butters’ and

chocolate and peanut butter spread mixes.

The first standard of identity and quality grading system for peanut butter in the United

States was established in 1942, and later published by the Food and Drug Administration (FDA)

1964 (Shurtleff & Aoyagi, 2015). The standardization states that peanut butter must contain at

least 90% ground peanuts with no more than 55% fat content. Additional ingredients up to 10%

may be included and accounted for in the ingredient and nutritional information such as

seasoning and stabilizing ingredients. Other ingredients permitted include emulsifiers such as

lecithin, however, addition of artificial colours, flavours and vitamins are restricted. Though the

establishment of a standard of identity for peanut butter allows for product transparency and

quality, it also restricts product innovation. For example, in the case of the development of low-

fat peanut butters, these products did not meet the FDA’s “peanut butter” standards and therefore

were required to be labelled as “peanut spreads” (FDA, 2009, 2014). Canada does not have a

specified standard of identity for peanut butter, therefore, if the product does not disclose the

21

peanut content (voluntary), this value remains unknown to the consumer and the company keeps

the recipe proprietary (Schwartz, 2011). However, strict ingredient and nutritional labelling

regulations allow consumers to evaluate differences between peanut butter or spread products.

Free oil present in unstabilized peanut butter is considered normal and slight to moderate

mixing should be able to disperse the separated oil within 30 to 35 seconds (USDA, 2011). For

stabilized peanut butter, there exists two grading categories for oil loss. For stabilized U.S. Grade

A, oil cannot be poured or collected and cannot flow when the container is tilted; for U.S. Grade

B, oil can be poured and/or flow when the container is tilted, however, collectable oil cannot

exceed 1 mL per pound of the product (USDA, 2011). Although, the natural gloss of both

unstabilized and stabilized peanut butter products is not considered free oil. In addition, the

texture should not be excessively sticky and should have a consistency such that it spreads easily

(USDA, 2011).

2.3.2. Peanut Butter Stabilizers

Peanut butter, like most other nut and seed spreads, shares a common structural

composition consisting of cell fragments suspended in oil released from the seed or nut during

grinding (Co & Marangoni, 2012; Rosenthal & Yilmaz, 2014). Currently, to produce “no stir”

peanut butters, stabilizers and emulsifiers are added in the grinding stage of production to

prevent particle settling and oil separation. Once all ingredients are uniformly dispersed, cooling

induces fat crystallization , creating a fat crystal network which immobilizes free oil and slows

phase separation, giving the peanut butter has a more desirable texture (Totlani & Chinnan,

2007). Storage temperature, conditioning, and melting point are important characteristics in

terms of stabilizer effectiveness in peanut butter. It has also been suggested that the stabilizer

22

adsorbs on the surface of the dispersed particles and stabilizes the suspension by repulsive forces

(Citerne, Carreau, & Moan, 2001).

Without a stabilizer, natural peanut butter is thin, flowable and phase separates in just a

matter of days, into free oil and solid meal which is dry, compact and un-palatable. Stabilizers

such as hydrogenated oils are most commonly used and are typically a mixture of rapeseed,

cottonseed, and soybean oil stabilizers and are typically added at 2% or less. This type of

stabilizer was the first viable solution to prevent oil separation in peanut butter and was

introduced in 1949 (Wait, 1949). It was during this time that Procter & Gamble Co. developed

the “Fix,” a new stabilizer to be used to produce a “no-stir” peanut butter. To this day, widely

used stabilizers include Fix-X (Procter & Gamble Co., Cincinnati, OH), Dritex RC Beads, and

Dritex RCS Beads (ACH Food Co., Memphis, TN), which contain >98% saturated fat and <0.5g

trans fat (Sanders & Carolina, 2001). Several alternative stabilizers have been a topic of

research, and can be found in both scientific and patent literature. Tropical oils have received a

considerable amount of attention, specifically palm oil (Aryana, Resurreccion, Chinnan, &

Beuchat, 2000; Gills & Resurreccion, 2000; Hinds, Chinnan, & Beuchat, 1994), which is

currently used in ‘natural’ or ‘organic’ no stir peanut butters and nut butters.

Hinds, Chinnan, & Beuchat (1994) studied at unhydrogenated palm oil as a stabilizer for

peanut butter at 2 to 4%. They predicted 2.0 to 2.5% palm oil would be effective in complete oil

stabilization for 1 year at 21-24C without any influence on colour. This prediction was based

on a 2 week accelerated stability tests conducted at 30 to 35 °C and based on the performance of

other commercial brand peanut butters and controls stabilized with Fix-X. The textural quality of

the palm oil samples were softer than tradition hydrogenated fat samples, though this difference

was attributed to samples being subjected to higher temperatures during setting and thus were not

23

able to achieve equivalent firmness to the commercial brands. This demonstrates that

conditioning is a critical factor for stabilizers that impart oil holding capacity via the formation

of crystals.

Gills & Resurreccion (2000) investigated peanut butter samples stabilized with 0, 1.5,

2.0, and 2.5% palm oil over time at storage temperatures of 0, 21, 30, and 45 °C. They found that

palm oil did not effectively stabilize peanut butter for >20 days at temperatures tested above zero

regardless of the concentration of palm oil. Though palm oil seemed to have an effect on

suppressing oxidized flavours.

Another method of stabilizing peanut butter that predates hydrogenated oil is the addition

of 1.5 to 2.0% glycerin (Du Puis, Segur & Lenth 1939). This method was reported to form an

emulsion between the oil and the solids, however, the time that this product would remain stable

was not reported. Other stabilizers that have been documented include silicon dioxide (Perlman

1999), propylene glycol (CENTIV, 2012), and chitosan (Schumacher 2000).

2.3.3. Textural Properties of Peanut Butter

Peanut butter has been described as a paste-like dispersion (Co & Marangoni, 2012;

Robins, 2000), or a highly concentrated suspension, where small (but not colloidal) solid

spherical peanut particles are dispersed in an oil continuous phase (Carreau et al. 2002). The

total lipid content of peanut butter is 47 to 50%, and the peanut oil consists of oleic acid (~52%)

and linoleic acid (~32%), with the remainder consisting of saturated fatty acids (Suchoszek-

Lukaniuk, Jaromin, Korycinska, & Kozubek, 2011). The product is naturally not structured by a

fat crystal network like other high fat foods, but rather, its stability comes from the close packing

of peanut particles within the continuous phase (Co & Marangoni, 2012). Carreau et al. (2002)

noted that peanut butter exhibits most of the rheological characteristics and complex nature

24

characteristic of suspensions of colloidal particles, with an increased complexity once stabilizers

are introduced. The approximate 50/50 solid particle/lipid composition of peanut butter results in

a suspension that approaches the close packing fraction. It has been estimated that the volume

fraction () an unstabilized “100% peanuts” peanut butter is 0.6, whereas the random close

packing fraction for monodispersed spheres is commonly accepted to be approximately 0.64

(Citerne et al., 2001; Poslinski, 1988). Though this system consists of polydispersed spheres

which are not at close packing fraction, particle-particle interaction still has a major effect on the

rheological properties of peanut butter, which may lead to the formation of a jammed network,

and therefore contribute to the solid-like character of both unstabilized and stabilized peanut

butter (Citerne et al., 2001; Mezzenga, Schurtenberger, Burbidge, & Michel, 2005). The particles

in peanut butter can have different shapes, sizes, size distributions and properties, for example,

peanut particles are spherical whereas cell wall fragments are irregular shaped. Peanut butter

exhibits most of the rheological characteristics and complex nature found with suspensions of

colloidal particles, with an increased complexity once stabilizers are introduced (Carreau et al.

2002).

For a non-self-supporting product like natural peanut butter (ie. cannot maintain specified

dimensions), it is necessary to contain the sample in a vessel and ensure the sample is not lifted

during the test (Annonymous, 2015). Instron type analysis is commonly used to mechanically

understand the textural attributes of samples. The parameters that can be extracted from the

force-deformation curve described in Ahmed and Ali (1986) consist of 1) firmness; the

maximum force of penetration, 2) absolute adhesion; the maximum force to overcome the

attractive forces between 2 contact surfaces, 3) work of adhesion; work needed to break contact

between the sample and the probe during withdrawal, and 4) stretch (or stringiness); the distance

25

the sample column stretched prior to breaking (Muego et al., 1990). With increased firmness or

maximum force of penetration, the sample is perceived as less wet or oily and has a lower

spread, meaning it is more self-supporting (Muego, Resurreccion, & Hung, 1990). For example,

natural peanut butter (0 wt% stabilizer) is the most liquid-like sample, it does not hold its shape,

but rather spreads outward on a flat surface, whereas when a stabilizer is added, peanut butter

begins to exhibit more solid-like behaviour and begins to hold its’ shape. The adhesion and work

of adhesion is correlated with the stickiness of the sample, or the force and work required to

remove peanut butter from the palate, tongue and teeth (Muego, Resurreccion, & Hung, 1990).

The stretch can be used to define a short texture, in which the material separates from the probe

quickly, or a stringy texture, where the material extends for a considerable distance before

breaking (Annonymous, 2015).

Ahmed and Ali (1989) found peanut butters containing higher amount of oil had lower

adhesion force and higher work of adhesion and stretch than samples containing a lower amount

of oil. They also found that oil content had more influence on adhesion parameters than percent

peanut seed content; peanut particle size was not analyzed during this study, but samples were

prepared on pressed and un pressed peanuts (for oil extraction), this initial particle size

difference in peanuts could have had an effect on final particle size distribution as all samples

were blended for 2 minutes (more chopping time results in finer particles). This suggests that

changing oil content, for the purposes of making a low-fat peanut spread for example, would

have a larger effect on textural parameters than peanut seed content.

Grind size is also an important parameter that has been shown to effect stickiness.

Crippen, Hamann, & Young (1989) stated that adhesiveness during mastication decreased as

particle size increased which is in support of the statement made by Woodroof et al. (1945) that

26

stickiness of peanut butter can be reduced by coarse grinding. Course grind size decreased

adhesiveness during mastication, spreadability decreased with increased grind size, and as grind

size increased-texture preferences decreased (Crippen, Hamann, & Young, 1989). However, a

coarse grind was significantly (p < 0.05) higher in instrumental hardness and adhesion than the

medium and fine grinds, therefore adhesion on Instron did not correlate with adhesion with

panelists (Crippen, Hamann, & Young, 1989). This lack of instrument and sensory panel

correlation can be attributed to Instron tests not taking into consideration other factors that affect

stickiness, specifically of nut butters or oil seed pastes that tend to readily absorb saliva in the

mouth resulting in an increase in stickiness and increased difficulty to swallow (Rosenthal &

Yilmaz, 2014). In addition, Instron testing exclusively measures vertical forces, whereas

chewing involves forces in both the horizontal and vertical planes.

2.3.3. Peanut Butter Microstructure

There is limited work looking at the microscopy of peanut butter. Due to the nature of the

product, it is difficult to observe how cell wall tissue fragments, protein bodies, starch granules

and any other additives are orientation in the oil continuous phase. To maintain structure of the

sample to the truest form possible, plastic embedding for light microscopy is used (Young &

Schadel, 1990). Young and Schadel (1990) viewed embedded peanut butter samples under light

microscopy and dehydrated and gold-palladium sputter coated peanut butter samples under

scanning electron microscopy (SEM). They concluded that limited information was attainable

about the homogeneity and spatial distribution of components in samples using SEM, but light

microscopy was able to provide information of the spatial relationship of peanut butter

components including the degree of dispersion, coalescence of protein bodies and the size of

tissue fragments. It was also reported that in their experience, cryostat sections resulted in

27

smearing during sectioning and is unsatisfactory for accurate interpretation. Samples shown were

three different commercially available stabilized peanut butters, any crystal formation in the oil

phase and mechanisms of stabilization was not explored.

The presence of protein body aggregates is undesirable in peanut butter microstructure

because it is an indication of oil loss, product hardening, and contributes to grittiness over time

(Aryana et al., 2000). In a study examining microstructure of peanut butter stabilized with 0, 1.5,

and 2.5% palm oil compared to hydrogenated vegetable oil, it was found at 0 °C storage all

samples exhibited a similar dispersion of particles in the oil continuous phase with no

aggregation or visible oil loss (Aryana et al., 2000). At storage temperatures of 45 °C, palm oil

treatments were found to have visible oil loss and exhibited protein body/cell wall fragment

aggregation with the oil continuous phase excluded from these aggregates. The size of the

aggregates decreased with increasing amount of palm oil, however, oil separation (that was not

significantly different) was observed for all samples at 45 °C storage. It was thought that oil

separation was due to the melting of palm fat crystals, however, smaller aggregates were

observed in 1.5 and 2.5% palm samples. This may have been caused by palm oil contributing to

oil stability via another mechanism, which was not explained. The control peanut butter

stabilized with 1.5% hydrogenated oil (Fix-X) was devoid of clusters when stored at 45 °C; its’

melting point is 71.11 to 73.89 °C (Procter and Gamble 1999), implying that peanut butter is

stabilized via a fat crystal network as no free oil was observed.

No oil separation was observed for all samples stored at 0 °C, but at storage temperature

of 21 °C, samples stabilized with 0 to 2.5% palm oil all exhibited oil losses approximately 14%

over a period of approximately 5 months (Gills & Resurreccion, 2000). At 30 and 45 °C, oil loss

increased to 14% over a period of 113 days, with oil loss plateauing at 153 days for all samples.

28

This indicates that peanut butter samples may only have a specific amount of oil available for

phase separation. Fix-X had the highest melting temperature of 71.11 to 73.89 °C (Procter and

Gamble; Aryana, 2000) followed by palm oil, 36 to 40 °C, and finally peanut oil at 3 °C. This

suggests that it is the solidification of the oil phase that prevents the aggregation of peanut

particles and oil separation. This may be why the same stabilization was observed for samples

stored at 0 °C, since all fat phases were solidified (Aryana et al., 2000). It wasn’t until starage

temperatures were increased that differences were seen in unstabilized, palm, and hydrogenated

oil peanut butter samples. However, it should be noted that hydrogenated vegetable oil

commercial stabilizers do not form gels at low incorporation levels in oil, because the critical

concentration of a commercial stabilizer gel is ~6.5 wt% (Blake & Marangoni, 2015), therefore it

can be assumed that not all oil is immobilized and the fat phase is not at a gelled state when

incorporated into peanut butter at concentrations of ~2%. Another factor to consider for oil

stability in peanut butter is the morphology of the stabilizer. Conditioning has been shown to be

a critical factor when using stabilizers that form crystals. Ward (1950) showed that rapidly

cooled peanut butter resulted in oil separation, whereas slow cooling yielded a more stable

product. Therefore, it is expected that fat crystal formation and stabilizer morphology is an

important factor that affects oil binding ability. In addition, any temperature fluctuation would

likely effect crystal growth and therefore effect oil stability.

2.4. Cream Filling

Sandwich biscuits and cream filled cookies are the fastest growing section of biscuits in

the US, with a commercial value of >$3 billion USD in 2014 (Euromonitor International, 2014a).

These products consist of a cream that is sandwiched between cookies or wafer sheets. There

exists a wide variety of different types of fillings or toppings used to enhance the appearance and

29

taste of a variety of baked goods. Icings, frostings, toppings, filling, buttercreams etc. are all

terms used to describe these spreadable semisolid products that have specific characteristics

depending on the baked good they are intended for use. The characteristics and properties that

distinguish one from another are not well defined, and the majority of formulation research exists

in patents and as company proprietary recipes. In general, the creams used as sandwich cookie

fillings are mainly comprised of sugar and hardstock fat (25 to 40%), with minor components

including starches, water, gelling agents, flavour and colouring agents (Battaiotto, Lupano, &

Bevilacqua, 2013; Kanagaratnam, Mansor, Sahri, Idris, & Gopal, 2009; Shamsudin, 2009). The

fats commonly used include butter, margarine, palm fat, and hydrogenated oils; therefore, these

high-fat products present an opportunity for organogels. There is limited peer reviewed literature

on the reduction of PHOs in cream fillings, however, the following section reviews various

concerns with partially or fully substituting PHOs and other saturated fats with a fat mimetic.

2.4.1. Formulation Considerations

Whey protein isolate-xanthan gum complexes (WPXC) were used as a fat replacement to

partially replace shortening (50 or 75 wt%) in cake frosting and sandwich cookie filling

(Laneuville, Paquin, & Turgeon, 2005). Response surface methodology was used to optimize the

low-fat formulations based on WPXC viscosity and textural properties. WPXC cake frosting and

sandwich cookie filling textural, rheological, and melting profiles similar to those of full fat

controls were achieved, however, there were difficulties with water activity for the latter

application (Laneuville et al., 2005). The low-fat WPXC had a water activity (Aw) of 0.82 ±

0.02, this Aw is suitable for cake frostings, however, commercial sandwich cookie fillings had an

Aw ranging 0.4 to 0.53 (Laneuville et al., 2005). Since cookie biscuits are hydroscopic, expand

with moisture uptake, and have an Aw between 0.2 and 0.6, the moisture would migrate to

30

equilibrium resulting in separation of the cookie-cream interface, and a moist cookie without the

desirable crisp texture (Battaiotto et al., 2013; Laneuville et al., 2005). This is also a problem

with cream fillings formulated with highly saturated hard stock fat and unsaturated oils, where

migration of liquid oil leads to softening of the cookies and textural defects (Stortz et al., 2012).

In the case of the cream with significant water content, humectants and bulking agents may be

used to maintain a low Aw, and for a high fat content cream, a suitable structuring agent capable

of slowing or preventing oil migration is required. In addition, there are textural differences

among cake frostings and sandwich cookie fillings that need to be considered. A highly adhesive

product is undesirable because it would have a sticky mouth feel, a highly viscous product is

difficult to pump and extrude during processing, and a fluid-like product would not be suitable to

maintain its shape on the product (Laneuville et al., 2005). Soft textures are optimal in the case

of cake frostings in order to be spread thinly without breaking the cake crumb, whereas, firmer

textures are more desirable for sandwich cookie fillings in order to prevent cookie misalignment,

smearing, and shape maintenance, such that cream does not squeeze out when handled or bitten

(Kanagaratnam et al., 2009; Laneuville et al., 2005). It is also advantageous for cookie creams to

rapidly solidify after spreading to prevent these defects during packaging, storage and

transportation (Shamsudin, 2009).

Starch-lipid composites (SLC) have been a common replacement for the fat content in

high fat foods as the starch component imparts texture and viscosity and the lipid component

provides the taste, melting properties, and mouth feel characteristic of full fat products (Singh &

Byars, 2011). SLC was used as a shortening replacement in cake icing, the SLC samples had

hydrogenated fat contents of 1.2 to 12.8% fat and a constant 0.85 Aw , compared to the 21.5% fat

content and 0.84 to 0.85 Aw of the shortening control (Singh & Byars, 2011). It was found that

31

16 and 24% SLC content can be used to prepare cake icings with as low as 6% fat content with

similar characteristics as the shortening control (Singh & Byars, 2011). Melting behaviour of the

SLC icings was observed at higher temperatures than the shortening control icing, indicating that

these low fat icings would hold their shape in the mouth when consumed instead of melting like

the shortening control (Singh & Byars, 2011). This high temperature melting behaviour,

although advantageous for shelf life, may result in a waxy mouth feel.

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38

CHAPTER 3

Oil stabilization of natural peanut butter using food grade polymers

ABSTRACT

The application of freeze dried hydroxylpropyl methylcellulose (HPMC) and methylcellulose

(MC) as stabilizers in peanut butter were investigated. These cellulose derivatives were dispersed

in water and subsequently freeze dried and chopped to produce a stabilizer that is able to absorb

high amounts of oil. Without this templating approach, HPMC and MC had no effect on peanut

butter stability and texture. An alternative spray drying approach was attempted, however, it was

found high incorporation levels were required to have a stabilizing effect. Centrifugal accelerated

stability testing showed a significant reduction in oil leakage for samples stabilized with freeze

dried HPMC and MC at addition levels as low as 0.4 wt% in peanut butter, while at addition

levels of 2.2 wt%, no oil loss was observed. With the addition of >1 wt% HPMC/MC, peanut

butters were shelf stable for 6 months or longer. Textural quality of the peanut butter was

investigated using a penetration test. Addition of freeze dried HPMC/MC increased sample

firmness and adhesiveness which mimicked the properties of traditional peanut butter products

stabilized with hydrogenated vegetable oils. Light and scanning electron micrographs showed

morphology differences among the stabilizer preparation methods and structural changes in

stabilized peanut butter samples. These experiments helped gain insight into the mechanism of

oil entrapment and demonstrated the potential of these food-grade polymers as stabilizers in food

systems.

Keywords: Peanut butter; HPMC; MC; Oil loss; Saturated fat; Organogel

39

1. Introduction

The health effects of dietary fat consumption and the associated risk of cardiovascular

disease (CVD) has been a controversial area of research over the past several decades (Ascherio

et al., 1996; McGee, Reed, Yano, Kagan, & Tillotson, 1984) . The aim to reduce the

consumption of saturated fat began with an epidemiological study, called the Seven Countries

Study (Keys, 1970), which postulated a positive association between high intake of saturated fats

and risk of CVD, and a negative association between high intake of monounsaturated fats and

risk of CVD. Since that time, many concerns regarding the validity of the Seven Countries Study

have been raised (Reiser, 1973). In addition, multiple observational and experimental trials have

shown contradictory results regarding the negative health effects of saturated fat consumption

(Shekelle et al., 1981; McGee, Reed, Yano, Kagan, & Tillotson, 1984; Ascherio et al., 1996; Hu,

Manson, & Willett., 2001). This controversy has also been a prevalent subject in main stream

media (Walsh, 2014). However, current governmental recommendations in many countries,

including Canada and the US, is to limit consumption of major sources of saturated fats to under

10% total caloric intake, to keep intake of trans fat as low as possible, and replace saturated fat

wherever possible with foods rich in mono-unsaturated and poly-unsaturated fats (FDA, 2015;

Health Canada, 2012; USDA, 2015). Recently, the generally recognized as safe (GRAS) status

of partially hydrogenated oil (PHO) was removed by the FDA with a three year compliance

period (FDA, 2015). This decision was based on the consensus of scientific evidence that shows

that consumption of trans fat from PHOs is associated with increased risk of CVD and the

promotion of insulin resistance in humans leading to the onset of pre- and type 2 diabetes (AHA,

2014; FDA, 2015; Hu et al., 2001).

40

The replacement of saturated fats in processed food products is not easily achieved

without negatively altering organoleptic properties, because saturated fats provide multiple

functions in foods such as textural, structural, and oil binding properties (Co & Marangoni,

2012). The motivation of this work was to find an alternative strategy to replace hydrogenated

stabilizers in peanut butter without the addition of saturated fat. Peanut butter, like most other nut

and seed spreads, shares a common structural composition consisting of plant cell fragments

suspended in oil released from the seed or nut during grinding (Co & Marangoni, 2012;

Rosenthal & Yilmaz, 2014). Currently, “no stir” peanut butters are produced with stabilizers and

emulsifiers that are added during the grinding stage of production to prevent particle settling and

oil separation. Once all ingredients are uniformly dispersed, cooling induces fat crystallization

that creates a fat crystal network that immobilizes the free oil and slows phase separation, giving

the peanut butter a more desirable texture (Totlani & Chinnan, 2007). It has also been suggested

that the stabilizer adsorbs on the surface of the dispersed particles and stabilizes the suspension

by repulsive forces (Citerne, Carreau, & Moan, 2001). Without a stabilizer, natural peanut butter

is thin, flowable and phase separates into free oil and solid meal, which is dry, compact and un-

palatable, in just a matter of days. Stabilizers such as hydrogenated oils are most commonly used

and are typically a mixture of rapeseed, cottonseed, and soybean oil stabilizers; typically added

at 2% or less. Widely used stabilizers usually contain >98% saturated fat and include products

such as Fix-X (Procter & Gamble Co., Cincinnati, OH), Dritex RC Beads, and Dritex RCS Beads

(ACH Food Co., Memphis, TN) (Sanders & Carolina, 2001). In 2014, the retail value sales of nut

and seed spreads in the US was approximately $2 billion USD, accounting for nearly half of the

value of the entire spreads commodity, which also includes chocolate spread, honey, jams and

preserves, and yeast based spreads (Euromonitor International, 2014). The value of nut and seed

41

spreads has increased by 13.5% in the past 5 years, largely due to the increase in diversity of

products like niche spreads, such as almond butter, cashew butter, tahini and several other nut

and seed spreads. These products have been shown to have healthy lipid profiles and are gaining

popularity due to their compliance with the current health and wellness trend among consumers

(Euromonitor International, 2014; Gorrepati, Balasubramanian, & Chandra., 2014).

Peanut butter has been described as a paste-like dispersion (Robins, 2007; Co &

Marangoni, 2012), or a highly concentrated suspension, where small (but not colloidal) solid

spherical peanut particles are dispersed in an oil continuous phase (Carraeu, Cotton, Citerne, &

Moan, 2002). The total lipid content of peanut butter is 47-50%, and the peanut oil consists of

oleic acid (~52%) and linoleic acid (~32%), with the remainder consisting of saturated fatty acids

(Suchoszek-Lukaniuk, Jaromin, Korycinska, & Kozubek, 2011). The product is naturally not

structured by a fat crystal network like other high fat foods, but rather, its stability comes from

the close packing of peanut particles within the continuous phase (Co & Marangoni, 2012).

Carreau, Cotton, Citerne, and Moan (2002) noted that peanut butter exhibits most of the

rheological characteristics and complex nature characteristic of suspensions of colloidal

particles, with an increased complexity once stabilizers are introduced. The approximate 50/50

solid particle/lipid composition of peanut butter results in a suspension that approaches the close

packing fraction. It has been estimated that the volume fraction of an unstabilized “100%

peanuts” peanut butter is 0.6, whereas the random close packing fraction for monodispersed

spheres is commonly accepted to be ~0.64 (Poslinski, 1988; Citerne, Carreau, & Moan.,

2001).Though this system is not at close packing, particle-particle interaction still has a major

effect on the rheological properties of peanut butter; this may be caused by jamming, and

42

therefore contribute to the solid-like character of both unstabilized and stabilized peanut butters

(Citerne, Carreau, & Moan, 2001; Mezzenga, Schurtenberger, Burbidge, & Michel, 2005).

An alternative stabilizer for peanut butter that has been a topic of research is palm oil

(Hinds, Chinnan, & Beuchat, 1994; Aryana, Resurreccion, Chinnan, & Beuchat, 2000; Gills &

Resurreccion, 2000), which is currently used in ‘natural’ or ‘organic’ no stir peanut butters and

nut butters. Other stabilizers that have been mentioned include glycerin (Du Puis, Segur &

Lenth, 1939), silicon dioxide (Perlman, 1999), propylene glycol (CENTIV, 2012), and chitosan

(Schumacher, 2000). Recently, edible organogels have become a popular strategy to replace

saturated fats in a variety of food products (Marangoni & Garti, 2011; Rogers et al., 2014). Many

structuring agents for organogels have been reported with potential for edible applications. They

include monoacylglycerides (MAGs), ricinelaidic acid, 12-hydoxystearic acid (12-HSA),

ethylcellulose, cerimides, and wax esters (Marangoni & Garti, 2011). Work done by Patel,

Schatteman, Lesaffer, and Dewettinck (2013) found an alternative way to structure oil using a

food grade polymer, which they referred to as foam templated organogels. In this work, a

hydroxypropyl methylcellulose (HPMC) solution was foamed and freeze dried to create a porous

structure which was shown to absorb a high amount of oil. Since freeze drying creates an open

cell structure, oil will be released under compression. To prevent this, the oil saturated foams

were sheared to disperse the polymer sheets and trap the oil (Patel, Schatteman, Lesaffer, &

Dewettinck., 2013). Other templating methods using methylcellulose (MC) and HPMC based

organogels have been used in cake batters (Patel et al., 2014; Patel & Dewettinck, 2015). Since

the HPMC foam templated organogels were obtained via shearing they show shear stability and

may be useful in spread-like food products. If the stabilizer was shear sensitive, once the

consumer spooned into the product, it would result in the structure breaking and oil pooling.

43

Another recent application of cellulose based freeze-dried foams have been oil absorbents

used as an alternative method to cleaning oil spills in water (Korhonen, Kettunen, Ras, & Ikkala,

2011). These applications however, typically are not food grade, which makes HPMC foams

unique and useful for food applications. HPMC and MC gums have been used in the food,

cosmetic, and pharmaceutical industries for decades and both have been granted a GRAS status

by the FDA.

HPMC and MC are well known for their ability to create gels in aqueous solutions, but

literature is limited on their use in oil based systems. As the understanding of food systems

becomes increasingly important in order to design functional components, component

interactions, particle stability, phase separation and liquid-like to solid-like behaviour transitions

need to be examined in individual food systems (Mezzenga, Schurtenberger, Burbidge, &

Michel., 2005). In the present study, HPMC and MC were investigated for their oil binding

capabilities as possible stabilizers in natural peanut butters.

2. Materials and Methods

2.1. Sample Preparation

2.1.1. Stabilizer Preparation

Hydroxypropyl methylcellulose (HPMC; TIC Gums TICACEL824-MP Powder,

Mississauga, ON) and methylcellulose (MC; TIC Gums TIACELMC LV) were dissolved in

distilled water to produce 1 wt% fully hydrated solutions. To facilitate dissolution of the

polymers, the powder was first dispersed in the presence of ice and then the remainder of the

water was added and continuously stirred overnight.

The HPMC and MC stabilizers were prepared by using an approach adapted from Patel,

Schatteman, Lesaffer, and Dewettinck (2013). The solutions were foamed in 500mL batches

44

using a hand-held food processor (Model 4166, Braun, Germany) at high setting for 6 min.

Aqueous foams were then poured into 11.5 x 18cm aluminum pans, frozen at -80°C and

subsequently freeze dried (UniTop 600SL, the Virtis Company, Gardiner, NY). In order to

incorporate into peanut butter, the dried foams were chopped in a small food processor (Model

MB1001, Magic Bullet, China) for 40 seconds in small batches (approximately 1 cup capacity).

As an alternative method to produce templated foams, a spray drying technique was also

explored. Spray dried foams were produced by preparing a solution of 0.5 wt% HPMC in water.

This solution was spray dried with an inlet temperature of 120°C, outlet temperature of 75-80°C,

100 aspirator %, and 40 pump % (BÜCHI Mini Spray Dryer, Model B-290, Switzerland). The

spray dried material was used in preliminary trials to examine its effectiveness as a stabilizer,

however, results were found to be unfavourable in terms of its oil binding capacity and this

methodology was therefore not further investigated.

2.1.2. Structured oil

Chopped, freeze dried HP/MC foams were mixed by hand with peanut oil (100% pure

peanut oil, Loblaws, Toronto, CA) to obtain samples containing 2, 3, 4, 5, and 10 wt% freeze

dried material.

2.1.3. Peanut butter

Two unstabilized natural commercial brands of peanut butter were used as base material

for stabilization and texture experiments (denoted Natural Brands A and B). Samples were

prepared by mixing peanut butter and HPMC/MC in a plastic bag for 2 min to produce 0.4, 0.6,

0.8, 1.0, and 2.2 wt% HPMC/MC in the peanut butter. The unaltered HPMC and MC powders

were used as a control additive. An upper limit of 2.2 wt% addition was utilized because

commercial peanut butter products are stabilized with hydrogenated oils and/or tropical oils up to

45

2 wt%. Alternative stabilizers which require well over 2 wt% addition to achieve optimal

stabilization and textural effects would therefore be unappealing to the industry. Two stabilized

commercial brands of peanut butter (denoted St-1 and St-2) stabilized with hydrogenated

vegetable oil were used as industry standards throughout this study. All products are categorized

as smooth peanut butters.

2.2. Peanut Butter Analysis

2.2.1. Total Fat and Protein Content

Total crude fat was determined following the AOAC Petroleum Ether Extraction Method

(Ahmed & Ali, 1986; AOAC, 2000). A small amount of peanut butter (2.0-2.5g) was spread onto

a cut strip of #4 Whatman filter paper (Fisher Scientific, Ottawa, ON), rolled, placed into a

cellulose thimble, and covered with glass wool. Samples were then washed with petroleum ether

in a reflux Soxhlet apparatus for approximately 5 hours. Once fat extraction was completed,

remaining solvent was removed in a forced air oven set at 100°C. The cellulose thimbles were

allowed to dry and the defatted peanut flour was collected. Crude protein content was determined

following the AOAC Generic Combustion Method (AOAC, 2000) using the conversion factor of

5.46 (AOAC, 2000). Samples were tested in triplicate.

2.2.2. Particle Size Distribution

Defatted peanut flour was dispersed in solution according to Lima, Guraya, and

Champagne (2000). 0.5g of defatted peanut flour was dispersed in 5mL of 2-propanol and

sonicated for 5 min. Particle size distribution was measured using the Mastersizer (Malvern

Mastersizer 2000, Malvern International Ltd., UK). Samples were vortexed for approximately

30 seconds before being added dropwise into the Mastersizer until a laser obstruction of 12-15%

was obtained. Samples were tested in triplicate.

46

2.3. Oil Loss

2.3.1. Structured oil

Oil loss of samples were evaluated using a modified net test (Barbut, 1996). The test was

performed by placing ~3g of sample into an inner tube with a perforated bottom to allow for oil

drainage, thus removing the possiblity of reabsorption. The perforations consisted of 22 holes

with ~0.79mm diameter. The inner tube was inserted into a 50mL centrifuge tube and

centrifuged at 100g for 10 min at 22°C (Model 5810 R, Eppendorf AG, Hamburg, Germany).

2.3.2. Peanut butter

Five grams of sample was put into 50mL centrifuge tubes and centrifuged at 1258g for 10

min at 22°C. Surface oil was removed after centrifugation and percent loss was calculated. Five

subsample measurements were completed at each trial/treatment combination. Percent oil loss

was calculated based on weight after stabilizer content was corrected. Real-time oil loss was also

quantified for on samples stored at ambient conditions as days until free oil flowed when the

container was tilted (USDA, 2011).

2.4. Texture Analysis

Samples were spread and leveled into petri dishes (100mm x 15mm) and stored at

ambient conditions over night. A texture analyzer (TA-XT2, Texture Technologies Corporation,

Scarsdale, NY, USA) equipped with a 30kg load cell was used for texture analysis. A penetration

test was adapted from Ahmed and Ali (1986) where a 2.5cm diameter acrylic cylindrical probe

penetrated 4mm at 0.5mm/s and was then retracted until the sample column completely broke

from the probe. The petri plate was divided into 4 quadrants and 4 subsample measurements

were completed at each trial/treatment combination. All measurements were performed at room

47

temperature. The textural parameters were extracted from the force-deformation curves as seen

in Figure 1, as described by Ahmed and Ali (1986).

Fig. 1. Characteristic force-deformation curve of a stabilized peanut butter samples. Texture

parameters interpreted include firmness (A), stretch (B-D), adhesion (C), work of penetration (1),

adhesiveness (2).

2.5. Microstructure

2.5.1. Light Microscopy

Structured oil samples were prepared by placing a small amount of sample onto a glass

microscope slide. The samples were then covered and pressed using a glass coverslip in order to

obtain a thin sample for observation. Slides were observed using a phase contrast light

microscopy (Model BX60, Olympus Optical Co, Ltd, Japan) and images were captured using a

digital camera (Model DP71, Olympus Optical Co, Ltd, Japan).

Peanut butter samples (approximately 0.5g) were extruded from a plastic bag, pre-fixed,

dehydrated, embedded in paraffin, and stained with hematoxylin-eosin following the procedure

48

outlined by Youssef and Barbut (2009). Slides were observed using a light microscope and

images were captured using a digital camera.

2.5.2. Scanning electron microscopy (SEM)

HPMC and MC samples were mounted on a pin stub using carbon tape, sputter coated

with ~20nm of gold-palladium, and trasferred to the SEM specimen chamber (Hitach S-570,

Tokyo, Japan). Specimens were observed under vacuum using an accelerating voltage of 10kV at

ambient temperature and digital images were captured (Quatz PCI Imaging Software, Version 8,

Quartz Imaging Corp., Vancouver, BC).

2.5.3. Cryo-SEM

Peanut butter samples were fixed to the surface of the holder (Emitech K1250X Cryo-

preparation unit, Ashford, Kent, UK) by applying a bonding agent (Tissue-Tec O.C.T

Compound, Canemco Supplies, St. Laurent, QC). The apparatus was then put under vacuum and

submerged into liquid nitrogen slush at -210°C to flash-freeze the sample. Once frozen, samples

were transferred under vacuum to a cryo-preparation unit. The portion of the samples protruding

from the holder was freeze-fractured using a blunt wedge to expose the internal structure.

Samples were then sputter coated with ~20nm of gold-palladium and transferred to the cryo-

SEM chamber under vacuum. Digital images were obtained using an accelerating voltage of

10kV.

2.6. Statistical Analysis

A completely randomized block with three independent trials was used. Two peanut

butter types, two polymer types, two preparation methods and six concentrations of polymer

(2x2x2x6 factorial). A software package (GraphPad Prism 5, GraphPad Software, Inc., San

Diego, CA, US) was used to perform a one way ANOVA and a Tukey post-hoc test for peanut

49

butter fat and protein content data on industry standard and base peanut butter samples.

Statistical analysis for oil loss and textural parameters were performed using the mixed

procedure (SAS Version 9.4, SAS Inst., Cary, NC, USA). An arc-sine square root transforamtion

was used on oil loss data and logrithmic transformations were used on textural parameters to

stabilize variances. A Brown & Forsythe test was performed to compare variances between

peanut butters, polymers, preparation, and among polymer concentration levels. An orthogonal

contrast was used to test for linear or quadradic trends as polymer concentration increased and to

test whether trends differed among peanut butter, polymer and/or preparation types. Industry

standard peanut butters were not included in statistical analysis for oil loss and textural

parameters, but were used as benchmarks.

3. Results and Discussion

3.1. Peanut butter fat, protein and particle size analysis

Table 1 summarizes the total fat, available oil, and crude protein content of the industry

standard peanut butters 1 and 2 (stabilized with hydrogenated oil) and the natural peanut butter

brands A and B, which were used as the base material for experimental treatments. Standard 2

had a higher total fat content (55.8±1.6%) and less protein (19.6±0.2%) than standard

1(50.2±0.4%, 21.0±0.2%). Natural peanut butter brand B had higher protein content, but there

was no significant difference between the fat content (Table 1). The available oil, refers to the

amount of oil centrifuged out at high centrifugal force, and is treated as the maximum amount of

oil able to phase separate during storage. Overall, this is the amount of peanut oil that needs to be

stabilized in the peanut butter, which differs from total fat content because a large amount of oil

is either already stabilized by being adsorbed to the surface of peanut particles, or still retained in

cell bodies within the peanut butter. This difference in oil contents would not be able to migrate

50

to the surface/phase separate during long term shelf storage. With long term storage, the total oil

loss of unstabilized peanut butter samples was ~14% (Gills, L.A. & Resurreccion, 2000), which

is in agreement with samples in this study.

Table 1

Total fat content, available oil and crude protein for the industry standard brands (St-1 & St-2)

(stabilized with hydrogenated vegetable oil) and natural peanut butter brands (Nat-A & Nat-B)

(base material for treatments).

Sample Total Fat Content (%) Available Oil (%) Crude Protein (%)

St- 1 50.2±0.4a 13.3±0.4a 21.0±0.2a

St- 2 55.8±1.6b 13.1±0.6a 19.6±0.2b

Nat- A 50.9±0.4a 14.9±0.01ab 22.7±0.1c

Nat- B 52.5±1.5ab 15.5±0.03b 24.8±0.1d

Mean ± standard error; values with different letters in columns are significantly different

(P<0.05).

Figure 2 shows the particle size distribution of the standard peanut butters (Fig. 2a) and

natural peanut butters (Fig. 2b). The standard peanut butters have a similar particle size

distribution. The natural brand A has a larger volume of smaller particles which has been shown

to result in less oil loss due to a increase in total particle surface area, resulting in more oil

associated with the surface of the particles and a decreased amount of oil available for separation

(Lima, Guraya, & Champagne, 2000). Although the standard brands of peanut butter have the

same general particle size distribution profile, it should be noted that they are stabilized with

hydrogenated vegetable oil, and contain other additives including soybean oil (St-2 only), corn

maltodextrins (St-2 only), molasses (St-1 only), sugar, salt, mono- and diglycerides.

51

Fig. 2. Particle size distribution of industry standard peanut butter brands- 1 and 2 (stabilized

with hydrogenated vegetable oil ) (a) and natural peanut butter brands A and B (base material for

treatments) (b).

3.2. Oil Loss

3.2.1. Structured oil

The oil binding capabilities of freeze dried HPMC and MC were evaluated at 2 to 5 and

10 wt% in peanut oil using centrifugation to promote oil loss. The addition of HPMC/MC

powder displayed no oil holding capacity; particles were merely wetted by the oil and then

sedimented. It was found that freeze dried HPMC is able to more effectively bind oil than MC at

all polymer concentrations tested (Fig. 3). At 10 wt% HPMC/MC in oil, the volume of polymer

added was excessive and resulted in a dry, crumbly powder. Although this concentration results

in very little to no oil loss, it would have negative effects on food applications at this level, as

will be discussed below. The 2 to 5 wt% HPMC/MC structured oil samples retained between 45

to 80% and 37 to 62% oil content respectively.

In our pretrial, samples prepared with <10 wt% spray dried HPMC in peanut oil resulted

in a viscous opaque white liquid. It wasn’t until 10 wt% incorporation that it resulted in a paste-

like material that did not flow, and 20% spray dried HPMC in peanut oil formed self-supporting

52

peaks analogous to whipped cream when mixed (data not shown). Since the amount of spray

dried material required to prevent oil from separating and impart structure far exceeds the

reasonable concentration (<10%), centrifugal tests were not conducted.

Fig. 3. Oil loss curves of freeze dried hydroxypropyl methylcellulose (HPMC) and

methylcellulose (MC) in peanut oil. N=3, Means±standard error.

3.2.2. Peanut butter

There was a significant interaction among the peanut butter types (Nat-A & Nat B),

preparation method (freeze dried vs. powder), and incorporation levels (Fig. 4). The accelerated

oil loss test by centrifugation shows that Brand B lost significantly more oil than Brand A

(P<0.05), even though the total and available oil contents of each are not significantly different

(see Sec. 3.1). The difference in oil loss can thereby be attributed to the difference in particle size

distribution, where Brand B had a larger volume percent of smaller particles, resulting in a larger

surface area for oil to absorb to (Lima, Guraya, & Champagne., 2000). It can then be understood

that the rate of oil loss of Brand A would be lower than Brand B as a result of its particle size

distribution. High centrifugal force resulted in oil loss that was not significantly different

(available oil), but at the lower (optimized) centrifugal force, Brand A lost significantly less oil

53

than Brand B. This effect, is very prominent in the powder samples with increasing polymer

concentration (Fig. 4a), however, with the addition of the freeze dried polymers, the effect is not

constant with increased polymer concentration (Fig. 4b).

The addition of HPMC/MC in original powder form (unaltered) had no significant effect

on the stability of either peanut butter brand with increasing polymer concentration (P>0.05)

(Fig.3a). Addition of freeze dried HPMC/MC was found to be more effective than the unaltered

powder in stabilizing the peanut butter with increasing polymer concentration levels (P<0.05)

(Fig.3). There was a decrease in oil loss with increasing polymer concentration of the freeze

dried HPMC and MC for both Brands A and B. This is likely due to the increase in polymer

sheets available to interact and create a network that would entrap oil, as well as an increased

surface area allowing for possible interactions and adsorption of oil at the polymer interface

(Patel, Schatteman, & Dewettinck., 2013).

HPMC and MC are water soluble polymers, however, they both have available hydroxyl

groups capably of hydrogen bonding, as well as methyl groups available for non-polar

interactions (Cash & Caputo, 2010). It has previously been reported that adding water to an oil

seed paste (14-20%) initially raised the pastes’ viscosity as the suspended particles started to

adsorb water, resulting in greater retention of the oil phase and gradual paste hardening (Kinsella

& Lindner, 1991; Rosenthal & Yilmaz, 2014). Though once the system contained higher water

levels the material phase separated and began to emulsify the oil (Kinsella & Lindner, 1991;

Rosenthal & Yilmaz, 2014). This stabilization effect could be due to hydrogen bonding and non-

hydrodynamic (Van der Waals) interactions or the adsorption of water and other hydrophilic

entities to the surface of the dispersed particles resulting in steric stabilization, much like the

stabilization of colloidal particles by polymers (Kinsella & Lindner, 1991; Citerne, Carreau, &

54

Moan, 2001). Rheometric characterization of HPMC structured oils suggest that the they are held

together by weak internal (Patel & Dewettinck, 2015). Though the addition of HPMC/MC could

increase possible non-hydrodynamic and steric interactions, it is likely that the physical

entrapment of the oil in the polymer network accounts for the majority of oil stability.

In a pretrial, spray dried HPMC was tested as a possible stabilizer and it was found that at

concentrations of 2.2 wt% the oil loss for peanut butters A and B were 5.2±0.08% and 5.6±0.1%

respectively. This is an equivalent stabilization as seen with 1.0-1.5 wt% addition of freeze dried

HPMC. Therefore, spray dried HPMC was determined to be less effective in stabilizing oil than

the freeze dried HPMC. This may be due to the greater volume of spray dried material that is

needed in order to achieve particle interactions, or a jammed system which builds a network to

entrap oil. This gives an indication that the morphology of HPMC is an important characteristic

that contributes to its ability to bind or entrap oil in the food system (see Sec. 3.4.1).

Fig. 4. Effect of hydroxypropyl methylcellulose and methylcellulose control powder (HPMC-

C/MC-C) or hydroxypropyl methylcellulose and methylcellulose freeze dried material (HPMC-

FD/MC-FD) to natural peanut butter brands A and B on percent oil loss. The dotted lines in (b)

show the value of the commercial standards 1 and 2 stabilized with hydrogenated vegetable oil.

55

Table 2 shows the time for oil loss (oil flows in container when tilted) in real time at

ambient conditions to determine if treatments would remain shelf stable. Oil separation in natural

peanut butter occurred within 2 days and samples containing 0.4 to 1.0, 2.2 wt% HPMC/MC

powder separated by day 3. The samples prepared with 0.4 to 1.0 wt% freeze dried HPMC and

MC also separated by day 3. Only the sample containing 2.2 wt% freeze dried HPMC/MC

remained stable for an extended period of time (>6 months). A single trial was performed on

intermediate concentrations of freeze dried HPMC and MC from 1 to 2 wt%. It was found that

these samples were also shelf stable (>6 months), whereas the powder controls of the same

polymer concentration separated within 3 days. This indicated there is a threshold which needs to

be met; i.e., above 1 wt% addition of freeze dried HPMC or MC in order to have a comparable

stabilization to the commercial peanut butter standards at ambient conditions.

Table 2

Time until oil loss occurred for natural peanut butter stabilized with 0.4 to 1.0 and 2.2%

hydroxypropyl methylcellulose (HPMC)/methylcellulose (MC) powder (-C) and freeze dried (-

FD) material.

Sample Time Until Initial

Oil Loss

Natural 2 days

0.4-1.0, 2.2% HPMC-C 3 days

0.4-1.0% HPMC-FD 3 days

2.2% HPMC-FD >6 mo.

0.4-1.0, 2.2% MC-C 3 days

0.4-1.0% MC-FD 3 days

2.2% MC-FD >6 mo.

3.3. Texture

With increased firmness or maximum force of penetration, the sample is perceived as less

wet or oily and has a lower spread, meaning it is more self supporting (Muego, Resurreccion, &

Hung, 1990). For example, natural peanut butter (0 wt% stabilizer) is the most liquid-like

56

sample, it does not hold its shape, but rather spreads outward on a flat surface, whereas when a

stabilizer is added, peanut butter begins to exhibit more solid-like behaviour and begins to hold

its’ shape. The adhesion and work of adhesion is correlated with the stickiness of the sample, or

the force and work required to remove peanut butter from the palate, tongue and teeth (Muego,

Resurreccion, & Hung, 1990). The stretch can be used to define a short texture, in which the

material separates from the probe quickly, or a stringy texture, where the material extends for a

considerable distance before breaking (Annonymous, 2015).

There were significant textural differences among the peanut butters, preparation

methods, and polymer concentration levels. Brand A of the peanut butter was significantly

firmer, more adhesive, and more stretchy than peanut butter brand B (P<0.05) (Fig. 5a,c,e,g).

Ahmed and Ali (1989) found peanut butters containing higher amounts of oil had lower adhesion

force and higher work of adhesion and stretch than samples having a lower oil content. Crippen,

Hamann, and Young (1989) reported a decrease in sensory adhesiveness with increasing grind

size; instrumental results showed an increase in adhesion and hardness with an increase in grind

size. Though the total oil and available oil of peanut butter A and B are not significantly

different (see Sec. 3.1), the particle size distribution can account for the difference in firmness

and adhesion.

At 2.2 wt% HPMC/MC, samples had a high adhesion force that met that of standards 1

and 2; however, the work of adhesion was lower than that of the standards. This was caused by

the high volume of stabilizer added to the sample, resulting in samples that were not sticky, had a

short texture, and were mouldable. The higher adhesion force could have been caused by suction

as opposed to sample stickiness, since these samples had minimum stretch and did not adhere to

the probe.

57

The addition of HPMC/MC powder resulted in no significant textural changes within

each peanut butter grouping across concentrations (see first column Fig. 4). The freeze dried

material was significantly firmer, adhesive, and stretchier than the powder added treatments and

the effect of polymer concentration level on firmness, adhesion and stretch were significant

(P<0.05).

58

Fig. 5. The effect of adding hydroxypropyl methylcellulose and methylcellulose powder (HP-

C/MC-C) or hydroxypropyl methylcellulose and methylcellulose freeze dried material (HP-

FD/MC-FD) to natural peanut butter brands A and B on textural parameters. The dotted lines

show the value of the commercial standard A and B stabilized with hydrogenated vegetable oil.

A

59

In a pretrial, peanut butters A and B with 2.2 wt% spray dried HPMC was evaluated for

textural properties and were significantly firmer, more adhesive, and stretchier than the control

samples with the equivalent concentration of powder HPMC added. The samples were also

visibly a lighter colour than the control powder counterparts. The same textural values can be

achieved with <1 wt% addition of freeze dried HPMC, with the exception of stretch, where the

spray dried additive resulted in a higher stretch value which can be interpreted as a more

cohesive product.

Table 3

The effect of adding 2.2% hydroxypropyl methylcellulose (HPMC) that was prepared by spray

drying (SD) or the control powder (C) to natural peanut butter brands A and B on textural

parameters.

Sample Firmness (N) [Adhesion] (N) Work of Adhesion

(mJ)

Stretch (mm)

A: 2.2% HPMC-

SD 0.70±0.01a 0.28±0.01a 2.69±0.08a 20.5±0.70a

B: 2.2% HPMC-

SD 0.36±0.01b 0.14±0.001b 1.50±0.02b 21.5±0.30a

A: 2.2% HPMC-C 0.15±0.004c 0.05±0.0005c 0.17±0.03c 12.6±0.19b

B: 2.2% HPMC-C 0.09±0.003d 0.03±0.0008d 0.089±0.02d 11.4±0.14c

Means ± standard error, values with different letters are significantly different (P<0.05)

3.4. Microstructure

3.4.1. Additive and Structured oil

The scanning election micrographs show the morphology of the native HPMC powder

(Fig. 6a) and the porous sponge structure (Fig.6c). Once the material is sheared to be

incorporated as an additive, the large pore structure is destroyed (Fig.6d). Smaller pores are still

seen within the sheets of the polymer, and these sheets, when combined with oil create a network

that physically entraps the oil and provides a large surface area for polymer/oil associations

(Patel, Schatteman, Lasaffer, & Dewwttinck, 2013). Preparing the HPMC via spray drying (Fig.

6b), and comparing the morphology to that of the freeze dried HPMC (Fig.6d) gave insight as to

B

60

what structure is better for oil binding and whether the physical morphology or the chemical

nature of the material plays a more dominant role in oil binding capabilities. For example, it

would be expected that MC would have better oil binding capabilities due to it being a more

hydrophobic molecule than HPMC (both are amphiphilic). Evidence suggests that a fibrillar

morphology would have better oil binding capabilities than a small crystal morphology (or

spherulitic) similar to that of wax oleogels (Dassanayake, Kodali, Ueno, & Sato, 2009). This is

due to the fibres’ ability to form entangled and densely structured networks that are able to

entrap large volumes of the oil phase as compared to small crystals which require higher

volumes of stabilizer to reach the gel point or the point where flow is not observed when the

substance is inverted in a container (Dassanayake, Kodali, Ueno, & Sato, 2009). As discussed in

section 3.2.2, the freeze dried material (Fig.2d), which is comprised of sheets, is more effective

in stabilizing oil than the small spherical particles in the spray dried additive (Fig.2b). Figure 7

shows that both freeze dried HPMC and MC create a network of individual polymer sheets in oil

which entraps oil, similar to the images shown by Patel, Schatteman, Lasaffer, and Dewwttinck,

(2013). With increasing concentration of these polymers, the sheets become more densely

packed and would thus provide a more tortuous network, enhancing oil stability.

61

Fig. 6. SEM micrographs of hydroxypropyl methylcellulose (HPMC): control powder (a), spray

dried HPMC (b), freeze dried HPMC xerogel (c) and sheared freeze dried HPMC xerogel (d).

62

Fig. 7. Light micrographs of 3% hydroxypropyl methylcellulose (a-b) and methylcellulose (c-d)

in peanut oil. Low magnification images (a,c), high magnification of isolated polymer sheets

(b,d).

3.4.2. Peanut butter

Cryo-SEM images (Fig. 8) show an increased amount of small fragments present in the

peanut butter when the polymer additive is present. The microstructural features consist of

broken cell wall fragments, protein bodies, starch granules and in the case of the freeze-dried

sample (Fig. 8b) carbohydrate sheets (Aryana et al., 2000; Young & Schadel, 1990). This was

confirmed with staining of light microscopy slides (Fig. 9), where samples containing HPMC

and MC have more fragments obstructing the aggregation of protein bodies. This potentially

allows for more surface available for oil adsorption. Light micrographs (Fig. 9) show similar

63

microstructure, demonstrating that the HPMC and MC addition has minimal effect on

microstructure of peanut butter.

Fig. 8. Cryo-scanning electron microscopy images of (a) natural peanut butter brand B, and (b)

peanut butter brand B with 1.5% wt. freeze dried hydroxylpropyl methylcellulose added.

64

Fig. 9. Light microscopy image of protein bodies (p), cell wall fragments (w), and starch

granules (s) dispersed in the oil matrix of (a) natural peanut butter Brand A, (b) hydrogenated

commercial standard A, (c) natural peanut butter brand A with 1.5% freeze dried HPMC, (d)

natural peanut butter brand A with 1.5% freeze dried MC.

4. Conclusions

Freeze dried HPMC and MC is a possible alternative stabilizer to hydrogenated oils in

peanut butter and may be applied to other nut and seed butters that exhibit similar structural

properties. At addition levels between 1-2% the desirable oil stability and textural properties of

commercial products (i.e., using hydrogenated oil stabilizers) can be met. The main mechanism

of stabilization is likely due to physical entrapment of oil within an interacting network of freeze

dried HPMC/MC sheets. Spray dried HPMC was used in preliminary trials to examine its

effectiveness as a stabilizer however, was found to be less effective than freeze drying. Possible

65

further research could be conducted such as using more efficient methods to prepare the dried

HPMC and MC additive than freeze drying such as extrusion, or optimizing spray drying.

Acknowledgements

The authors would like to acknowledge the financial support provided by Ontario

Ministry of Agriculture and Food and Ministry of Rural Affairs (OMAF and MRA).

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69

CHAPTER 4

Hydroxypropyl methylcellulose and methylcellulose structured oil as a replacement for

shortening in sandwich cookie creams

ABSTRACT

The partial and full substitution of icing shortening with freeze dried hydroxylpropyl

methylcellulose (HPMC) and methylcellulose (MC) structured canola oil in sandwich cookie

cream was investigated. The cellulose derivatives were prepared using a foam templating

approach and incorporated as a shortening replacer in food applications. Treatments were

formulated with a 40 wt% fat component and 60 wt% icing sugar, with icing shortening being

replaced at 50, 75, and 100% with HPMC or MC structured canola oil. These treatments were

compared to a 100% shortening control and commercial sandwich cookie cream as an industry

benchmark. Shelf life of cookie creams was effectively improved with increasing level of

shortening replacement; the amount of unbound oil decreased as a higher amount of oil adsorbed

to the surface of added polymer sheets. It was found that the shortening control resulted in highly

sticky and gummy creams, while shortening replacement at 50 and 75% gave similar large

deformation textural properties as the commercial benchmark. Full replacement resulted in

creams that were excessively hard. The storage modulus of creams were used as an interpretation

of stiffness, and showed that shortening replacement increased stiffness to match the commercial

benchmark. As a rheological fingerprint, nonlinear, large amplitude oscillatory shear Lissajous

plots were used to show differences among samples at stresses beyond the linear regime. Based

on these results, it was found that cookie creams with desirable functional behaviour can be

made by replacing shortening with HPMC- and MC-structured canola oil at intermediate levels.

70

Keywords: icing; cookie cream; hydroxypropyl methylcellulose, HPMC; methylcellulose, MC;

Oil loss; Saturated fat

1. Introduction

Many food products are formulated with high amounts of saturated and/or trans fats

because these fats contribute to desirable flavours, textures, mouthfeel, and functionality of the

product (Co & Marangoni, 2012). Current governmental recommendations in many countries,

including Canada and the US, are to limit consumption of major sources of saturated fats to

<10% total caloric intake, to keep intake of trans fats as low as possible, and replace saturated fat

with foods rich in mono-unsaturated and poly-unsaturated fats, wherever possible (FDA, 2015;

Health Canada, 2012; Uauy et al., 2009). Additionally, the FDA recently announced their

finalized decision to remove the generally recognized as safe (GRAS) status of partially

hydrogenated oils (PHOs), providing a three year compliance period (FDA, 2015). This decision

was based on the consensus of scientific evidence which has shown that the consumption of

industrial trans fats, mainly from PHOs, is associated with increased risk of cardiovascular

disease (CVD) and the promotion of insulin resistance in humans, leading to the onset of pre-

and type 2 diabetes (AHA, 2014; FDA, 2015; Hu, Manson, & Willett, 2001). As a result,

research on strategies to replace saturated and trans fats in food products without negatively

affecting the organoleptic properties has been an increasingly pressing concern for the food

industry. Icings, frostings, and cream fillings are of particular concern, as they are traditionally

comprised of predominantly sugar and fat, and often contain 25-40% fat from butter, margarine,

hydrogenated oils, and/or palm-based shortenings (Battaiotto, Lupano, & Bevilacqua, 2013;

Kanagaratnam, Mansor, Sahri, Idris, & Gopal, 2009; Shamsudin, 2009).

71

Sandwich biscuits and cream-filled cookies are the fastest growing section of biscuits in

the US, with a commercial value of >$3 billion USD in 2014 (Euromonitor International, 2014).

These products consist of a confectionary cream that is sandwiched between biscuits or wafer

sheets. Though seemingly simplistic in their composition, reformulation of icing-type products is

challenging, as saturated or trans fats cannot be directly replaced with liquid oil without

negatively impacting the properties of the final product. For example, replacement of the fat

component with canola oil results in significant oil leakage during storage, reducing the shelf-life

of the product (Stortz, Zetzl, Barbut, Cattaruzza, & Marangoni, 2012). There are a wide range of

icing-type products used as adjuncts to cakes and baked goods with other basic or functional

ingredients including water, egg whites, gelatine, gums, modified starches, flavour, and

colouring agents (Bennion & Bamford, 1973). Although the characteristics and properties that

distinguish sandwich cookie creams from other filling and topping products are not well defined,

in general, cookie creams must be quick setting, firm at ambient temperatures, impart a smooth

and creamy mouthfeel, and have minimal or no oil/moisture loss, as this leads to softening of the

cookies and textural defects (T. A. Stortz, Zetzl, Barbut, Cattaruzza, & Marangoni, 2012). A

highly adhesive cookie cream would also undesirable because it would have a sticky mouth feel.

In terms of processing, a thixotropic behaviour would be ideas as a highly viscous product would

be difficult to pump and extrude, whereas a more fluid-like product would result in a runny

cream filling (Laneuville, Paquin, & Turgeon, 2005). In addition, the cream must be firm enough

to prevent cookie misalignment, smearing, and be able to maintain its shape such that the cream

does not squeeze out when handled or bitten (Kanagaratnam et al., 2009; Laneuville et al., 2005).

Palm-based shortenings (e.g., modified palm oil and palm kernel oil) have been

extensively used in icing-type products in attempt to replace PHOs, with a high degree of success

72

(Kanagaratnam et al., 2009). However, as noted above, there is increasing concern about the use

of this tropical fat, specifically its high saturated fat content and sustainability issues. Starch and

gum components have also been used to partially or fully substitute shortening in icing products

(Laneuville et al., 2005; Singh & Byars, 2011). Saturated fat replacement with refined

carbohydrates, however, has also been a cause of concern because low-fat, high-carbohydrate

diets are associated with a different set of health issues including dyslipidemia, a component of

metabolic syndrome (Forsythe et al., 2008; USDA, 2015; Volek, Fernandez, Feinman, &

Phinney, 2008). Therefore, the Dietary Guidelines Advisory Committee recommends that

emphasis should be put on optimizing dietary fat consumption with foods high in unsaturated

fats without reducing total fat consumption (USDA, 2015).

Recently, structured edible oils (organogels) have been recognized as one of the most

promising and versatile strategies to replace fats rich in saturated and trans fatty acids in food

products (Marangoni & Garti, 2011; Rogers et al., 2014). Several mechanisms of oil structuring

have been reported, using multiple different structuring agents that can be loosely defined under

the following categories: crystalline particles, crystalline fibers, structured emulsions, polymeric

strands (Marangoni & Garti, 2011), and, more recently, inorganic particles (Patel, 2015). Patel,

Schatteman, Lesaffer, and Dewettinck (2013) recently reported an alternative method to structure

oil using water soluble food grade polymers using a foam templating approach. A solution of

hydroxypropyl methylcellulose (HPMC) was foamed and freeze dried to create a porous

structure which has been shown to absorb a high amount of oil. The freeze drying process creates

an open cell structure which releases oil under compression. To prevent this, oil saturated foams

were sheared to disperse the polymer sheets and effectively trap the oil (Patel, Schatteman,

Lesaffer, & Dewettinck., 2013). Templated oils using methylcellulose (MC) and HPMC have

73

been successfully used as shortening replacements in cake batters (Patel et al., 2014; Patel &

Dewettinck, 2015). In the present study, HPMC- and MC-structured oils were investigated for

their potential in partially and fully substituting shortening in sandwich cookie creams.

2. Materials and Methods

2.1. Structured Oil Preparation

HPMC (TIC Gums TICACEL824-MP Powder, Mississauga, ON) and MC (TIC Gums

TIACELMC LV) were dissolved in distilled water to produce 1 wt% fully hydrated solutions.

The HPMC and MC template structures were prepared using an approach adapted from

Patel, Schatteman, Lesaffer, and Dewettinck (2013). Each solution was foamed in 500 mL

batches using a hand-held food processor (Model 4166, Braun, Germany). Aqueous foams were

then poured into 11.5 x 18 cm aluminum pans, frozen at -80 °C overnight and subsequently

freeze dried (UniTop 600SL, The Virtis Company, Gardiner, NY). In order to facilitate

incorporation into cookie creams, before being added to oil, the dried foams were chopped in a

small food processor (Model MB1001, Magic Bullet, China) for 40 s in small batches (~1 cup

capacity). Chopped, freeze dried HPMC and MC foams were mixed by hand with canola oil

(Saporito Foods, Markham, ON) to obtain samples containing 3 wt% freeze dried material

(determined in pre-trials to be an optimal level). Additional trials were performed to confirm that

without this templating approach, HPMC and MC had no oil structuring effect, and could not be

used as a shortening replacer.

2.2. Cookie Cream Preparation

Cookie creams were prepared using icing sugar (Lantic, Toronto, ON), HPMC- or MC-

structured canola oil, and icing shortening (Cargill, 51685-TransAdvantages, Charlotte, North

Carolina). A series of cookie creams with an increasing percentage of the fat phase were replaced

74

with HPMC- or MC-structured canola oil (50, 75, 100 wt% of the fat phase). Samples were

prepared by blending the structured oil with the shortening content (when applicable), followed

by incorporation of the icing sugar by hand and mixing until a homogeneous paste was obtained.

The formulations investigated are outlined in Table 1.

Table 1 Composition of experimental cookie creams containing hydroxypropyl methylcellulose

(HPMC) and methylcellulose (MC) structured oil at different substitution levels (0, 50, 75, and

100%).

2.3. Total Fat and Fatty Acid Composition

The fatty acid composition of several commercial cookie creams and the commercial

icing shortening were determined using Gas Liquid Chromotography (GLC). The fat content was

first extracted from cookie creams following the Petroleum Ether Extraction Method (AOAC,

2000). A small amount of cookie cream (2.0-2.5 g) was spread onto a cut strip of #4 Whatman

filter paper (Fisher Scientific, Ottawa, ON), rolled, placed into a cellulose thimble, and covered

with glass wool. Samples were then washed with petroleum ether in a reflux Soxhlet apparatus

for approximately 5 hr. Once fat extraction was completed, the remaining solvent was removed

in a forced air oven at 100 °C. The extracted fat samples were prepared for GLC analysis using a

transmethylation reaction method adapted from Christie (1982). Extracted fat content (20 mg)

was dissolved in 1 mL of sodium-dried diethyl ether and 40L of methyl acetate. 40 L of 1 M

sodium methoxide in dry methanol was subsequently added and agitated to ensure mixing for 5

Sample

% Fat from

Structured

Oil

Composition (wt%)

Canola Oil HPMC/MC Icing

Shortening Icing Sugar

Ctrl 0 0 0 40 60

50HPMC 50 19.4 0.6 20 60

75HPMC 75 29.1 0.9 10 60

100HPMC 100 38.8 1.2 0 60

50MC 50 19.4 0.6 20 60

75MC 75 29.1 0.9 10 60

100MC 100 38.8 1.2 0 60

75

min at room temperature. The reaction was then stopped by adding 60 L of a saturated solution

of oxalic acid in diethyl ether, with brief agitation. This mixture was centrifuged at 1500 g for 2

min and the solvent was removed using a nitrogen stream at room temperature. Finally, the dried

precipitate was mixed with 0.5 mL of diethyl ether and an aliquot was taken directly for GLC

analysis. Fatty acid methyl esters (FAME) were determined using a capillary GLC equipped with

a 60 m BPX7-column of 0.22 mm internal diameter with 0.25 mm film thickness (SGE Inc,

Austin, TX, USA) housed in a Agilent 6890-series Gas Chromatograph (Agilent Technologies,

Inc., Wilmington, DE, USA) with a 7683-series auto-sampler. The oven increased from 110 to

230 °C at a rate of 4 °C min-1 and was maintained at 230 °C for 10 min. The injector and detector

temperatures were 240 and 280 °C, respectively. Hydrogen gas was used as the carrier, with an

average velocity of 25 cm s-1, and peaks were identified by comparison to FAME standards.

2.4. Oil Loss

Oil loss over time was evaluated following the methods described in Dibildox-Alvarado,

Rodrigues, Gioielli, Toro-Vazquez, & Marangoni (2004). Briefly, cookie creams were moulded

into sample disks (2 cm in diameter, 3 mm thick) by spreading samples into moulds and

refrigerating for 1 hr to facilitate removal. The amount of oil that each sample lost to filter papers

(110 mm diameter) at 25 °C was determined by weighing filter papers before and after the

storage period. Oil loss was calculated using the following formula:

(1) 𝑜𝑖𝑙 𝑙𝑜𝑠𝑠 = 𝑤𝑡.𝑝𝑎𝑝𝑒𝑟 (𝑡)− 𝑤𝑡.𝑝𝑎𝑝𝑒𝑟 (𝑡=0)

𝑤𝑡.𝑑𝑖𝑠𝑐 (𝑡=0) × 100%

Samples were tested in duplicate, at times 0.5, 1, 2, 3, 4, 5, 6, 12, and 24 hr; each with five sub

samples (five separate sample disks each on different filter papers).

76

2.5. Texture Profile Analysis (TPA)

Samples were spread into moulds (10mm in diameter, 5mm thick) and refrigerated for 1

hr to facilitate removal. A texture analyzer (TA-XT2, Texture Technologies Corporation,

Scarsdale, NY, USA) equipped with a 30 kg load cell and an acrylic compression plate (10 cm in

diameter) was used to perform texture profile analysis (TPA) (Bourne, 1978). Samples were

compressed to 50% of their original height, at room temperature, for two cycles at a testing

velocity of 1.5 mm/s. The resultant force-deformation curves were used to derive instrumental

TPA parameters, including: hardness; the peak force during the first compression; adhesiveness;

the work of the first decompression; cohesiveness, work ratio of the second and first

compression; and gumminess, computed as the product of the hardness and cohesiveness

(Bourne, 1978). These parameters are the focus of discussion as they are most relevant for these

soft solid materials.

2.6. Small and Large Amplitude Oscillatory Shear Rheology

Rheological experiments of cookie creams were determined using a stress sweep (10 to

3000 Pa) maintained under isothermal conditions (25 °C), at a constant frequency of 1 Hz using

a controlled stress rheometer (TA Instruments model AR2000). A steel parallel plate geometry

(upper plate diameter: 40 mm) covered with sandpaper on both the upper and lower plate to

prevent slip, set to a gap of 1 mm, and set with an equilibrium time of 10 min for all

measurements.

2.6.1. Small Amplitude Oscillatory Shear Rheology

Small amplitude oscillatory shear (SAOS) was used to determine storage and loss moduli

(G’, and G” respectively) of the cookie creams in the linear viscoelastic range at oscillatory

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stress from 10 to 100 Pa. Yield stress was taken as the stress where G’ departed from the linear

viscoelastic region.

2.6.2. Large Amplitude Oscillatory Shear Stress (LAOStress) Rheology

Raw stress and strain data in the nonlinear region (~500 to 3000 Pa) were normalized and

Lissajous curves were constructed. Plots at increasing stress amplitudes were normalized in order

to more accurately see differences between curves to assist in visual analysis. It is important to

note that differences in cookie creams in this study are distinguished in terms of 2-dimentional

space within curves derived from increasing stress amplitude, using a stress-controlled rheometer

at a single frequency. While in the linear viscoelastic region (LVR), material response would be

the same for controlled-strain and controlled-stress approaches, while outside the LVR, the

material response is dependent on which of these two methods is used (Dimitriou, Ewoldt, &

McKinley, 2013).

2.8. Statistical Analysis

The GraphPad Prism software package (version 5.0, GraphPad Software, Inc., San

Diego, CA, US) was used to perform one way ANOVA and Tukey post-hoc tests for sample

comparison. Oil loss was normalized and fitted to a two-phase association with the model

plateau constrained to 100% (i.e., predicted plateau could not exceed 100% oil loss).

3. Results and Discussion

3.1. Total Fat and Fatty Acid Content

Due to the lack of a published standard sandwich cookie cream formulation, several

commercial brand products were evaluated. The fat content of the commercial cookie cream

icings ranged from 27-44 % total fat (Table 2). According to the ingredient listings, the fat used

in these products includes one or a mixture of the following: modified palm oil, modified palm

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kernel oil, soya oil shortening, coconut oil, and vegetable oil (mixtures of canola, soybean,

cottonseed). The major fat constituents in all products included palmitic and oleic acid.

Therefore, an icing shortening containing similar fatty acid profile was selected as the control fat

component in cookie cream treatments, which were formulated with constant 40% fat and 60%

sugar content. The first commercial cookie cream, CS1, is the leading sandwich biscuit currently

on the market, therefore it was selected as an industry benchmark for treatment cookie creams

for the purposes of this study.

Table 2 Fatty acid composition and total fat content of commercial sandwich cookie creams, a

commercial shortening and canola oil. All values are reported in wt%.

Fatty Acid

Type

Icing

shortening

Canola

Oil1

CS1 CS2 CS3 CS4 CS5 CS6

12:0 0.3 16.3 14.5 27.7 44.4

14:0 1.1 0.9 0.9 8.0 6.5 12.2 17.3

16:0 45.0 4.0 38.8 38.2 37.3 31.9 15.5 11.2

18:0 5.1 1.7 4.2 5.0 5.9 4.0 9.6 5.5

18:1 39.0 62.5 37.0 35.7 24.7 29.2 9.8 8.8

18:2 8.9 19.8 15.9 16.9 4.0 8.33 17.1 1.0

18:3 12.0 1.4 1.0 2.7

Total Fat

Content

- - 44.0 27.2 39.4 29.0 32.7 37.8

1 (Zetzl, Marangoni, & Barbut, 2012)

3.2. Oil Loss

The amount of oil lost to filter papers provides an indication of the oil binding

capabilities of the sandwich cookie creams. An ideal cookie cream would have no, or very low

oil loss, as increased expulsion of the liquid oil leads to softening of the cookies and product

textural defects (Stortz et al., 2012). Percent oil loss is expressed as a function of time (Figure 1).

Oil loss was fitted to a two-phase association model, where the rate of oil lost is related to the

total storage time, using the following formula:

(2) 𝑌 = 𝑌𝑓𝑎𝑠𝑡(1 − 𝑒(−𝑘𝑓𝑎𝑠𝑡·𝑡)) + 𝑌𝑠𝑙𝑜𝑤(1 − 𝑒(−𝑘𝑠𝑙𝑜𝑤·𝑡))

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Where t is time (hr), Yfast is the percentage of oil lost during the fast phase component, Yslow is

the percentage of oil lost during the slow phase component, kfast and kslow are the rate constants of

each of these components, respectively. Thereby, oil loss was expressed as a sum of the fast and

slow component with the maximum oil loss being constrained to 100% (Table 3).

Fig. 1 Oil loss curves for (a) commercial standard (CS1, ) and shortening control (Ctrl, )

sandwich cookie creams compared to creams made with increasing shortening replacement from

(b) hydroxypropyl methylcellulose (HPMC), and (c) methylcellulose (MC) structured canola oil

(50, ; 75, ; 100, wt%).

The oil loss model postulates that the oil binding may exist as two distinguishable

mechanisms, 1) weakly stabilized oil (fast component), which exhibits short-term stability and 2)

stabilized oil (slow component), which exhibits long-term stability (Blake, Co, & Marangoni,

2014). The percentage of weakly stabilized oil present is highest in the shortening control cookie

cream (81.25 ± 7.02%) and significantly decreased as a higher level of structured oil was used to

replace the shortening component, with 50HPMC, 75HPMC, 100HPMC and 100MC having

significantly less unbound (or fast migrating) oil than the full saturated fat control (Table 3). The

substitution of HPMC structured canola oil at all levels tested, and 100% replacement of MC

structured canola oil effectively reduced the amount of oil lost. This can be attributed to the

presence of HPMC or MC sheets which provide a large surface area for association with the oil

phase (Patel, 2015). CS1 had a 51.28 ± 10.76% weakly stabilized oil content, in comparison with

the treatments being investigated, 100MC cookie cream had significantly less weakly stabilized

oil content (22.90 ± 2.95%), whereas, the weakly stabilized oil content of 75HPMC and

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100HPMC were lower than CS1, but not significant. Therefore, the long-term stability of the

cookie creams were improved with increasing content of HPMC- or MC-structured canola oil in

the shortening, despite a much higher content of unsaturated fatty acids. This indicates that

freeze dried HPMC and MC are effective in stabilizing a high amount of oil, resulting in cookie

creams that would be shelf stable in terms of oil expulsion over time.

Table 3 Fitted parameters of the fast and slow oil loss components (Y, component percent; k,

rate constant) obtained using a two-phase association model. Commercial standard (CS1),

shortening control (Ctrl), and sandwich cookie cream treatments made with increasing

shortening replacement (50, 75, 100 wt%) with hydroxypropyl methylcellulose (HPMC), and

methylcellulose (MC) structured canola oil.

CS1 Ctrl

50

HPMC

75

HPMC

100

HPMC

50

MC

75

MC

100

MC

Yfast (%) 51.28 ±

10.76ac

81.25 ±

7.02b

51.20 ±

3.41ac

35.69 ±

5.92ad

35.26 ±

3.10ad

75.20 ±

7.34bc

58.70 ±

6.39abc

22.90 ±

2.95d

Yslow (%) 48.72 ±

10.76ac

18.75 ±

7.02b

48.8 ±

3.41ac

64.31 ±

5.92ad

64.74 ±

3.10ad

24.80 ±

7.34bc

41.3 ±

6.39abc

77.1 ±

2.95d

kfast (hr-1) 0.15 ±

0.05b

0.12 ±

0.02b

0.17 ±

0.02ab

0.09 ±

0.04b

0.07 ±

0.02b

0.29 ±

0.04a

0.09 ±

0.02b

0.06

±0.02b

kslow (hr-1) 2.34 ±

1.20

1.39 ±

0.90

3.24 ±

0.66

2.84 ±

0.87

6.23 ±

3.35

4.50 ±

4.73

2.91 ±

1.56

3.38 ±

0.60

R2 0.67 0.88 0.95 0.71 0.80 0.88 0.63 0.84

Means ± standard error; values in rows with different letters are significantly different (P<0.05).

3.3. Texture

The relevant textural parameters of the commercial sandwich cookie creams are

summarized in Table 4. Despite being used for similar sandwich cookie products, CS 1 to 6

display several textural differences. As previously discussed, a desirable cookie cream would be

moderately adhesive, as to not impart a sticky mouthfeel, while being firm enough to maintain its

shape on the cookie so cream is not squeezed out when handled or bitten. The hardness values of

commercial products ranged from 0.41 ± 0.03 to 1.61 ± 0.002 N, with CS1 exhibiting an

intermediate degree of firmness. The adhesiveness, cohesiveness, and gumminess of the

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commercial products tested ranged from 0.10 ± 0.02 to 0.65 ± 0.02 g s, 0.14 ±0.01 to 0.49 ±

0.02, and 0.13 ± 0.02 to 0.33 ± 0.01 N, respectively. Cookie creams with shortening substitution

from HPMC- and MC-structured oil were considered acceptable within these ranges during

textural analysis, however, were directly compared to the most commercially successful

sandwich cookie biscuit, CS1. CS1 seemed to have intermediate hardness, and low adhesiveness,

cohesiveness, and gumminess, as compared to the other commercial products.

Table 4 Texture profile analysis parameters of commercial standard (CS) sandwich cookie

creams (1 to 6).

Sample Hardness

(N)

Adhesiveness

(J) Cohesiveness

Gumminess

(N)

CS1 0.88 ± 0.03b 0.97 ± 0.10b 0.14 ± 0.01b 0.15 ± 0.01ab

CS2 1.14 ± 0.04a 1.60 ± 0.08a 0.28 ± 0.01a 0.32 ± 0.02c

CS3 0.75 ± 0.02a 4.22 ± 0.13a 0.44 ± 0.01c 0.33 ± 0.01c

CS4 1.49 ± 0.10b 0.66 ± 0.13b 0.14 ± 0.05b 0.13 ± 0.02a

CS5 0.41 ± 0.03c 2.57 ± 0.19c 0.49 ± 0.02c 0.20 ± 0.02bd

CS6 0.65 ± 0.01c 2.63 ± 0.12c 0.40 ± 0.01c 0.26 ± 0.02cd

Means ± standard error; values with different letters within each column indicate significant

difference (P<0.05).

Full replacement of the shortening component with either HPMC- or MC-structured

canola oil produced cookie creams which were significantly harder than CS1, and both fell out of

range of acceptable hardness values (Table 5). Following the 100HPMC and 100MC samples,

the icing shortening control sample was the hardest. When compared to the control, as the

amount of shortening replacement increased (50 to 75%), hardness decreased; however, this

decrease was only statistically significant with the 50MC formulation. Otherwise, these creams

were not significantly different from the control. None of the 50 and 75% shortening replacement

creams were significantly different from CS1. The shortening control cream was significantly

more adhesive and as the replacement level of HPMC or MC structured oil increased, the

samples became less adhesive, approaching the adhesive properties of CS1. Although, the 100%

replacement samples had adhesive values which fell below the acceptable range. This same trend

was seen with cohesiveness, though all samples fell within the range of acceptability. Similarly,

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treatments with shortening replaced with HPMC- or MC-structured canola oil had lower

gumminess values than the icing shortening control; however, all treatment samples showed

higher gumminess than CS1.

Given the significantly lower textural parameter values seen with samples formulated

with HPMC- and MC-structured canola oil as compared to the shortening control cream, it can

be concluded that these materials behave differently in cookie creams. In particular, using icing

shortening used in cookie cream formulations in isolation resulted in highly sticky and gummy

cookie creams. Shortening replacement at 50 and 75% level resulted in similar values as seen in

the commercial product CS1, therefore, perhaps HPMC and MC are able to provide desirable

textual attributes that commercial products achieve with added minor components, such as

gelatine, gums, or modified starches. This demonstrates the ability cookie cream formulations

containing HPMC- and MC-structured canola oil to mimick commercial product behaviour

without the addition of other texture modifiers.

Table 5 Effect of 50, 75, and 100% shortening replacement with hydroxypropyl methylcellulose

(HPMC), and methylcellulose (MC) structured canola oil on texture profile analysis parameters

of sandwich cookie creams.

Sample Hardness

(N)

Adhesiveness

(J) Cohesiveness

Gumminess

(N)

CS1 0.88 ± 0.03d 0.97 ± 0.10bc 0.14 ± 0.01b 0.15 ± 0.01b

Ctrl 1.61 ± 0.06bc* 5.36 ± 0.38a* 0.40 ± 0.01a 0.64 ± 0.03a*

50HPMC 0.98 ± 0.02cd 1.31 ± 0.11bd 0.25 ± 0.01a 0.24 ± 0.01bc

75HPMC 1.39 ± 0.08cd 1.12 ± 0.07bcd 0.21 ± 0.01c 0.29 ± 0.02c

100HPMC 3.39 ± 0.38a* 0.53 ± 0.10c* 0.13 ± 0.01b 0.46 ± 0.06a*

50MC 0.84 ± 0.04d 1.81 ± 0.14d 0.35 ± 0.0a 0.30 ± 0.01c

75MC 1.05 ± 0.03cd 0.67 ± 0.07bc 0.21 ± 0.01c 0.22 ± 0.01bc

100MC 2.12 ± 0.20b* 0.43 ± 0.06c* 0.13 ± 0.01b 0.29 ± 0.04c 1 Means ± standard error; values with different letters in columns are significantly different

(P<0.05). 2 Values with an asterisk (*) fall out of the range of commercial cookie cream products.

3.4. Small Amplitude Oscillatory Shear Rheological Behaviour

The storage modulus and yield stresses of commercial cookie creams and treatment

cookie creams are shown in Fig. 2 and 3, respectively. Treatment samples with 100%

83

replacement of shortening with structured oil were too stiff for rheological analysis, which is

consistent with the textural results (section 3.3) where 100 % replacement samples were twice as

hard as the control shortening cream.

All samples exhibited G’ > G” for a large range of stress amplitudes, which is indicative

of the solid-like or elastic behaviour of cookie creams. The storage modulus gives an indication

of sample stiffness, which is an important property of cookie creams in terms of maintaining

cookie shape and integrity when handled or bitten. The commercial products investigated

exhibited a fairly wide G’ range. The G’ of CS6 was significantly lower than all other

commercial creams, followed by CS5<CS4<CS2<CS1<CS3. CS5 displayed one of the lowest

G’, but, the highest yield stress, indicating it is weak, but more resistant to non-recoverable

deformation under stresses, in comparison to CS6 which has a similar G’, but yields at a much

lower stress. In addition, as demonstrated by texture analysis, CS5 and CS6 are the softest

products. For the purposes of this study, cookie creams that were less easily deformed, with

behaviour similar to CS1 were considered desirable and are used as the benchmark for further

discussion.

The control cookie cream had the lowest G’ (0.66 ± 0.009 x106 Pa). The increase of G’

values follows 75MC<50HPMC<75HPMC<50MC, with only 75MC being significantly lower. It

is difficult to ascertain differences among the creams containing HPMC or MC, or the creams

with 50 and 75% shortening, as no overall trend is seen (Fig. 3). However, creams with 50 and

75% replacement of shortening with HPMC or MC structured canola oil had significantly larger

G’ values than the full shortening control. This indicates that stiffness is improved to more

similarly match CS1 with the addition of HPMC or MC shortening substitute, suggesting HPMC

84

and MC may play a role in imparting structure similar to that of CS1, while also reducing

saturated fat content.

The treatment cookie creams (Fig. 3c to f) all showed similar G’ and yield stresses,

indicating similar behaviour to CS1 (Fig. 3a), in comparison to the shortening control (Fig. 3b)

which exhibits a higher yield stress. Therefore, the addition of HPMC- or MC-stabilized oil may

be contributing to instability, causing the structure to break down at lower stresses than that of

100% shortening fat formulation, which more closely reflects behaviour of CS1.

85

Fig. 2 Stress sweeps for commercial standard (CS) sandwich cookie creams performed at a

constant 25°C. CS1 (a), CS2 (b), CS3 (c), CS4 (d), CS5 (e), CS6 (f).

86

Fig. 3 Stress sweeps for sandwich cookie cream samples made with increasing shortening

replacement (50 and 75) with hydroxypropyl methylcellulose (HPMC), and methylcellulose

(MC) structured canola oil performed at a constant 25°C. Commercial standard (a), icing

shortening control (b), 50 HPMC (c), 50 MC (d), 75 HPMC (e), 75 MC (f).

2.5. Large Amplitude Oscillatory Shear Stress Behaviour

To further investigate the behaviour of cookie creams, the rheological behaviour beyond

the LVR was analyzed. Lissajous curves were used to visually represent elastic deformation,

yield, and regain of plastic flow (Dimitriou et al., 2013). The differences in non-linear response

of each cream to high oscillatory stresses can be interpreted as a rheological fingerprint in the

87

non-LVR, giving qualitative information regarding material response as strain is decomposed

into an elastic and viscoplastic component (Dimitriou et al., 2013). For a purely elastic material,

the trajectory would be linear, approaching a straight line, while a trajectory approaching an

ellipse is characteristic of a viscoelastic material, and a cyclic curve will be observed for a purely

viscous material (Melito & Daubert, 2011). At low stresses, within the LVR, Lissajous curves

appear as tight ellipses or linear lines (not shown) as G’ >> G”, and the material displays purely

elastic behaviour with no area enclosed in the curve. As the stress amplitude is increased toward

the yield stress and beyond, materials exhibit Lissajous curves with an enclosed area, which is a

direct measure of energy dissipated in the material (Dimitriou et al., 2013). To assist in visual

analysis, plots were normalized to highest stress amplitude within each controlled-stress

oscillation in order to more accurately see differences between curves with increasing amplitude

and patterns among creams.

The Lissajous curves for commercial cookie creams show a range of patterns, which

distinguishes transitions from a viscoelastic to viscous behaviour within a sample, and identifies

how this transition differs between samples. For example, CS1, which had an intermediate

hardness, displayed a quick transition from viscoelastic to viscous behaviour, as indicated by the

dramatic increase in area enclosed by the curve at 2013 Pa to 2684 Pa (Fig. 4a). In comparison,

CS3, CS5, and CS6 have curves that progressively broaden with increasing stress amplitude,

indicating these creams exhibit a more gradual transition to purely viscous behaviour. It should

be noted that CS6 was characterized using lower stress amplitudes (Fig. 2f) due to the sample

being too soft to give responses at higher stress amplitudes. Interestingly, these samples are also

the softest creams among the commercial product tested (Fig.4 c, e, f). This directly contrasts

CS2 and CS4, which displayed the highest hardness values, and showed very gradual broadening

88

of curves with increased stress amplitudes, such that they do not display the higher proportion of

viscous behaviour within the tested stress amplitudes as the other commercial creams (Fig.4 b,

d).

Fig. 4 Lissajous plots for commercial standard (CS) sandwich cookie creams CS1(a), CS2 (b),

CS3 (c), CS4 (d), CS5 (e), CS6 (f), performed at a constant 25°C, at stress amplitudes of 551,

1510, 2013, 2684 Pa (97, 150, 201, 551 Pa for CS6).

89

Lissajous curves for creams made with increasing shortening replacement with HPMC-

or MC-structured canola oil, a 100% shortening control and CS1 are shown in Fig. 5. It was

expected that 50HPMC and 50MC would display more similar patterns to CS1 (Fig. 5 a) as they

had similar large deformation characteristics, however, both 50% shortening replacement

samples had similar gradual transitions from viscoelastic to viscous behaviour (Fig. 5 c, d). The

75% shortening replacement creams, and the 100% shortening control show very gradual

broadening of the curves with increased stress amplitude (Fig. 5 b, e, f). This may be related to

the higher hardness values these creams displayed, similar to the commercial sample that did not

undergo a behavioural transition within tested stresses. Typically, SAOS testing has been used to

understand icing-type product behaviour (Battaiotto et al., 2013; Singh & Byars, 2011), however,

many processes involving icing-type products, including, extrusion, pumping, chewing and

swallowing cause very large deformations at high stresses, which makes LAOStress a valuable

and underutilized method to further characterize rheological behaviour.

90

Fig. 5 Lissajous plots for sandwich cookie creams made with increasing shortening replacement

(50 and 75%) with hydroxypropyl methylcellulose (HPMC), and methylcellulose (MC)

structured canola oil performed at a constant 25°C, at stress amplitudes of 551, 1510, 2013, 2684

Pa. Samples shown are the commercial standard (a), icing shortening control (b), 50 HPMC (c),

50 MC (d), 75 HPMC (e), 75 MC (f).

4. Conclusions

The physical characteristics of sandwich cookie creams are not well defined and vary

among currently available commercial products. Oil loss, textural and rheological studies in the

LVR and non-LVR indicated that shortening replacement with canola oil structured with freeze

91

dried and chopped HPMC and MC imparts similar physical characteristics as commercial

products at 50 and 75% replacement levels for creams containing 40% fat content. The addition

of this shortening replacement results in creams having a lower saturated fat content, long term

oil stability, less sticky texture and exhibit rheological behaviour similar to that of the selected

commercial benchmark product than the all shortening control.

Acknowledgements

The authors would like to acknowledge the financial support provided by Ontario

Ministry of Agriculture and Food and Ministry of Rural Affairs (OMAF and MRA).

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CHAPTER 5

Conclusions and Future Directions

In this study, the oil holding capacity of freeze dried HPMC and MC foams were

investigated in two high fat food systems, peanut butter and sandwich cookie cream. Relatively

low concentrations (0.2 to 2.2, and 5% in peanut butter, and 0.6, 0.9, and 1.2% in cookie creams)

of HPMC or MC were able to stabilize large amounts of oil and be used as a full or partial

substitute for hydrogenated oils. It was found that the oil binding mechanism of these additives is

likely due to a combination of physically entrapped and adsorbed oil in a network of polymer

sheets. Morphology of HPMC and MC was determined to be a significant contributor to oil

binding capacity as addition of HPMC and MC in original powder form (unaltered) had no

significant effect on the stability of peanut butter with increasing polymer concentration,

whereas, freeze dried material did. The freeze dried and chopped material is comprised of sheets,

as compared to dense rod shaped particles of the unaltered HPMC. Spray dried HPMC, which

consists of small spherical particles, was determined to be less effective in stabilizing oil,

possibly due to a greater volume of spray dried material being needed in order to achieve particle

interactions, or a jammed system which builds a network to entrap oil. With increasing

concentration, freeze dried polymer sheets become more densely packed and would thereby

provide a more tortuous network, enhancing oil stability. This gives an indication that the

morphology of HPMC, and similarly MC, may play a more dominant role in oil binding than the

chemical nature of the material in terms of their ability to adsorb and entrap oil in a food system.

The substitution of shortening with HPMC- and MC-structured canola oil effectively reduced the

amount of oil loss in cookie creams over time. Using a two-phase association model, two

mechanisms of oil binding were distinguishable, fast oil loss or physically entrapped oil, and

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slow oil loss or adsorbed oil. It was found that as the level of shortening replacement increased, a

higher percentage of oil was stabilized, or adsorbed to particle surfaces in cookie creams as

compared to being weakly stabilized, exhibiting short-term oil holding. Therefore, the oil binding

capacity of freeze dried HPMC and MC can be attributed to a combinational effect of entrapment

and oil adsorption in peanut butter and cookie creams.

In terms of the effects of HPMC- and MC-structured oil on the quality and textural

properties of the two food systems:

Peanut butter with >1 wt% HPMC or MC were shelf stable for 6 months or longer

Freeze dried HPMC or MC increased sample firmness and adhesiveness successfully

mimicking the properties of traditional peanut butter products stabilized with

hydrogenated vegetable oil

Shortening used in isolation for cookie cream resulted in highly sticky and gummy

cream

Shortening replacement at 50 and 75% HPMC- and MC-structured oil gave similar

large deformation textural properties as the commercial benchmark

Full shortening replacement resulted in creams that were excessively hard, and too

stiff for rheological analysis

Storage modulus of creams, as an interpretation of stiffness, showed that shortening

replacement (50 and 75%) increased stiffness to match the commercial benchmark

Lissajous plots derived from LAOS data showed distinct “rheological fingerprints”

among creams

In attempt to improve the quality of these products, the addition of other supplementary

structuring agents may be useful, as HPMC and MC incorporation at higher levels resulted in

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peanut butters and icings that had a crumbly, firm texture. Combining other structuring agents,

for example stearic acid and stearol alcohol to supplement more oil binding capacity and add

plasticity may be useful. This may give these structured oils characteristics required for use in

other food applications such as pastry dough, which requires the ability to be sheeted or rolled

out thinly while maintaining structure. A significant disadvantage of HPMC and MC as a

structurant in the format explored in this work is water solubility. This limits the food

applications tremendously as with the addition of water, the oil binding capacity is diminished. It

would be advantageous to explore possible methods to stabilize the structure while maintaining

its ability to adsorb oil, for example, the use of crosslinking agents. In addition, further research

could be conducted such as using more efficient methods to prepare the dried HPMC and MC

additive than freeze drying such as extrusion, or optimizing spray drying.

For the food applications explicitly explored in this work, it would be advantageous to

study the oxidation stability of oils stabilized with HPMC and MC, as trans and hydrogentated

oils demonstrate oxidation stability and increased shelf life compared to liquid oils, this would be

an important consideration when reformulating food products. For the purposes of this study, a

constant fat sugar ratio was used to formulate cookie creams, it would be interesting to look at

the effect of lower levels of fat content and replacement of the lost fat content with sugar

replacements since, the addition of sugar content with the reduction of fat content simply creates

another health problem. In addition, further rheological studies, including SAOS and LAOS

would give a better understanding of desirable attributes of specific icing-type products such that

fat mimetics may be tailored for specific uses. LAOS studies are currently underutilized in food

research and can provide important information as it relates to effects of high stress exhibited in

food processing and eating. Understanding the melting profile of cookie creams using

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temperature sweeps would enable differences to be seen between shortening and HPMC- and

MC-structured oil and would give insight into heat stability of HPMC and MC, as well as key

sensory attributes, e.g., mouthfeel.

Functional properties of organogels themselves, and in food systems is important, as the

understanding of food systems has become increasingly important in order to design functional

components. This has been the main focus in edible organogel research. In this work,

composition, product stability, phase separation, texture, and solid-like to liquid-like behaviour

transitions were examined to demonstrate the potential of HPMC and MC as stabilizers and

shortening replacements in food systems. One area in particular that is lacking in edible

organogel research is sensory studies, including trained panels and consumer acceptability

testing to understand consumer perception as related to physio-chemical properties. This aspect

of fat memetic research is immensely important as it is sensory properties that drive consumer

acceptance, and in general trump the health benefits organogel products would have if they

exhibit perceivably lower quality organoleptic properties.

Edible organogels show great prospects for use as a hardstock fat mimetic in processed

food products, such as spreads, creams, cookies, pastries, cakes, and cheeses. It should be noted

that increased or excessive consumption of any one of these products in either their traditional

form or with incorporation of edible organogels would not be conducive to a healthy diet. The

intent of edible organogels is to replace trans and saturated fat content in processed foods in

order to create healthier, and more sustainable versions of so called ‘indulgence’ foods, and to

steer away from the “low-fat” diet that replaces fat content with refined carbohydrates. This will

enable the production of quality food products with consumer acceptance that have reduced trans

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and saturated fat content, thereby contributing to the reduction of metabolic syndrome, and the

onset of pre- and type 2 diabetes.