EFFECT OF VISCOSITY MODIFICATION BY FIBER DOSE AND HEAT TREATMENT ON

POSTPRANDIAL BLOOD GLUCOSE RESPONSE

Evelyn Y in-Y ue Wong

A thesis submitted in conformity with the requirements for the degree of M.Sc.

Graduate Department of Nutritional Sciences University of Toronto

0 Copyright by Evelyn Yin-Yiie Wong 1997

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7io m y parents,

PH a d Wedy

E m C T OF VISCOSITY MODIFICATION BY FIBER DOSE AND HEAT TREATMENT ON POSTPRANDIAL BLOOD GLUCOSE RESPONSE

Master of Science, 1997 Evelyn Yin-Yue Wong

Graduate Department of Nutritional Sciences University of Toronto

ABSTRACT

The effect of rnodifjmg viscosity by psylliurn dose and treatment methods on postprandial

blood glucose response was tested in healthy individuals (4M + 4F, 33.6S.5 years) on 20

occasions. Meals, either untreated or heat-treated, were composed of glucose solution (25g

or 50g CHO) with (test) or without (control) supplernentation of either 3, 6, or 9g psyllium.

Meai viscosity was determined by measuring hardness, which correlated with viscosity

(r=0.98, p=0.0034).

Log hardness of meals, which was directly proportionai to dose (r=0.99, p=0.0056)

and heat treatment of psyllium (p=0.0002), was inversely proportional to incremental

blood glucose area (AUC) at both 25g (-1 -00, p=0.000 1) and 50g (-0.94, p=0.0004)

CHO levels. AUC of meals of two dEerent nutrient levels only correlated to log hardness

after adjusting for the gram of carbohydrate in meals (-0.94, p<0.0001). Viscosity of

rneals, with nutnent levels taken into consideration, is an important parameter in

predicting postprandid blood glucose response.

ACKNOWLEDGEMENTS

First, 1 would like to thank my s u p e ~ s o r , Dr. Vladimir Vuksan, both for taking me as

a student, and for his unconditionai support and encouragement. Without his insightfùl

perspectives, patience and guidance, this work would not have been accomplished. I

would also like to thank Dr. TMS Wolever and Dr. AV Rao for being my advisory

cornmittee members, Dr. DIA Jenkins for being the appraiser and Dr. M Archer for being

a member of the examination cornmittee. Their valuable advice, direction and expertise

are greatly appreciated. Special thanks to Dr. L Thompson for her guidance throughout

the program.

1 am grateful to Dr. EH Kim for her technical assistance in the laboratory, Dr. CWC

Kendall for his critique of this work and Ed Vidgen for his help in statisticai anaiysis of the

data.

1 would like to thank my colleagues, Vernon and Brenda, for al1 the help and fun

during my study. Sincere thanks also go to the individuals who panicipated in my study.

Without you sacrificing your most enjoyable breakfasts, this study would never be

completed.

1 am gratefùl to the staff of the graduate department, in particular Brenda and Tina for

ail your assistance.

My deepest thanks go to my parents for their love and support. Vincent, thanks for

being there with me ail this t h e .

TABLE OF CONTENTS

Abstract

Acknowledgements .................................................................................. iii

Presentations .................................................................... vii

List of Tables ....................................................................................... viii

List of Figures .................................................................................... X.

List of Appendices . . . .......................................................................... . . . . . .... . . xii

List of Abbreviations .. ..... ................. .. .................... . . . . . . . . . . . . . . . . . . . . xiii

Chapter 1. Introduction and Literature Review 1.1 Introduction ..................................,..........-.........-.+............ . . . . . . . . . .. 1.2 Literature Review

1 -2.1 Historical aspects . .. . .. . .. . . .. . ... .... . . . ..... . .. . . ,....... .... . . . . . . . . . . . . . . . . . . . . . 1.2.2 Definitions and classifkation of dietary fiber . . .. . .. . . . .. .. .. . . . . . - - . . . . . 1.2.3 Physico-chemicai properties of soluble fiber ............... . . . . . . . . . . . . .

1.2.3.1 Hydration properties .. ........ . . ... . .. . . .. . ... -. .. . . .. . . .. ... . .... .. . . . . . . . . - 1.2.3.2 Rheology ... .. . . . . ... . .. . . .. - .. . .. . .. . . . . . . . . . . -. . . . . . . . . . .. . .. . . . . . . . . . . . . . .

1.2.3 -2.1 Viscosity .... .. .. . . .. . ... .. . .. .... . ... . . ... . -. . .-. ... . . . . . . . . . . . . . . . . . 1.2.3 -2.2 Hardness . - . . . . . . . . . . . , . . . . . . . . . . . . . -. . . . . - - . -. . - - . . . . . . . -. . .

1.2.4 Dietary fiber and disease ............................................................ 1.2.5 Mechanism of action of dietary fiber on carbohydrate metabolisrn . 1.2.6 Psyllium .................................... -. -. - . . . . . - . - . -. . . . . . *. . . . . . . . . . . . . . . . - 1.2.7 Uncertain aspects of soluble fiber . .. .................................. . . .- - - -.-

1 -3 Hypothesis and Objectives 1.3.1 Research questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . 1.3 -2 Hypothesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . *. . - - - -. . . . . . . . . . . . -. . - -. . . . . . . . . 1.3.3 Objectives . .. . .. ... .. . ... . . . . .. . .- -. - .. -. . . . .- .. . .........- - - -. -. . . . . . . . .. -. -. . - - -

Chapter 2. In Vitro Measurements: Effed of Fiber Dose and Processing M e h d s on RheoIogy

2.1 Introduction ... .. . .. . ..-. .. . .. ..- ... -. -. - - -. . .. . -.- .. - - - - - - - -. . . .. . - - -. . . . . 28 2.2 Materials and Methods ... -.. .-. ... ,.. . .. .-- ---. . ----..-..----.-* --. . - . . 28

3.3.3.2 Low nutrient levei (25g carbohydrate) ......................... 62 3.3.3.3 High nutrient level(50g carbohydrate) ........................ 64 3 -3.3 -4 Cornparison between low (25g) and high (5Og) CHO levels 64

3 -4 Discussion ......................................................................................... 69

Chapter 4 Generd Discussion and Conclusion ....................... ............................................... 4.1 Generai, discussion ,. 77

4.2 Implications and benefits .................................................... 80 ......................................................................................... 4.3 Conclusion 83

References cited .................................................................................................... 85

Appendices ....................................................................................... 95

PUBLISHED ABSTRACTS AND PRESENTATIONS

1. Oral presentation

Wong E W , Vuksan V. Effect of viscosity modification by fiber dose and heat treatment on postprandial blood glucose response. The Ciinical Research Society of Toronto, Toronto, Apnl 1996.

2. Poster presentation

Wong E W , Vuksan V, Kim EH, Sievenpiper J, Jenkins DJA. Effect of viscosity modification by fiber dose and heat treatment on postprandial blood glucose response. Experimental Biology 96 (FASEB), Washington DC, Apnl 1996.

LIST OF TABLES

Page

Table 1-1. Effea of adding guar gum to 50g CHO glucose mals on acute blood glucose and insulin responses in normal subjects .......... 21

Table 1-2. Effects of adding pectin and psyiiiurn to 50g CHO glucose meals on acute blood glucose and insuiin responses in normal subjects .......................................................................................... 23

...................................... Table 2-1. Composition of experimental rned samples 30

Table 2-2. Combination of different procedures in tests to determine the optimal viscosity level. ..................................................................... 3 2

Table 2-3. Observational results of heat-treated samples 24 hours after heat ... treatment, during re-heating, and 7 days after initial heat treatment 3 5

Table 2-4. Apparent viscosity rneasurements of ail 25g CHO untreated fiber ............. samples at dserent shear rates, 24 hours after initiai mixing. 38

Table 2-5. Apparent viscosity measurements of ail 50g CHO untreated fiber ............. samples at different shear rates, 24 hours after initiai rnixing. 38

Table 2-6. Hardness measurements of aii untreated and kat-treated samples at 25g and 50g CHO, 24 hours after initiai e n g . ............................ 41

.................................................................................. Table 3-1. Subject pronle. 48

Table 3-2. Blood glucose concentrations at specific time points, incremental area under the curves (AUC) and glucose peaks of different

......... untreated controI and fiber test meals at 25g CHO lwels (n=8) 5 5

Table 3-3. BIood glucose concentrations at s p d c time points, incremental area under the m e s (AUC) and glucose peaks of different

......... untreated control and fiber test meah at SOg CHO levels (n=8) 56

Table 3-4. Blood glucose concentrations at specific time points, incremental area under the curves (AUC) and glucose peaks of dierent heat-treated control and fiber test meah at 25g CHO levels (n=8) ..... 60

Table 3-5. Blood glucose concentrations at specific t h e points, incremental area under the airves (AUC) and glucose peaks of mirent

..... heat-treated control and fiber test meals at 50g CHO leveis (n=8) 6 1

Page

Table 3-6. Cornparison of fiber to nutrient ratio, hardness and the corresponding AUC per gram CHO, glycemic index and % redudon in AUC of al1 25g and 50g CHO untreated and heat-treated meals (n=8) . ...... ... ... ... ... ... ... ...... ... ... ... ... . . . . . . . . 67

LIST OF FIGURES Page

Fig. 1-1.

Fig. 2- 1.

Fig. 2-2.

Fig. 2-3.

Fig. 3-la.

Fig. 3-lb.

Fig. 3-2a.

Fig. 3-2b.

Fig. 3-3 a.

Fig. 3-3b.

Fig. 3-4a.

Fig. 3-4b.

Fig. 3-Sa.

Fig. 3 3 .

Correlation between % glucose reduction and gram of guar administered in five acute studies (n=8) ............................................. 22

Correlation between psyilium dose (3,6, and 9g) and apparent viscosity (shear 30 sec-') of 25g and 50g CHO untreated mals . .. .. . .... 39

Correlation between psyllium dose (3, 6, and 9g) and hardness of 25g and 50g CHO heat-treated and untreated meals ......................... 42

Correlation between hardness and apparent viscosity (shear 30 sec-') of 25g CHO untreated mals at different psylliurn doses (3, 6, or 9g) .... 43

Blood glucose response of untreated control and fiber test meals (3, 6, and 9g) at 25g CHO (n=8) .................................... .... ............. 53

BIood gIucose response of untreated control and Bber test meais (3, 6, and 9g) at 50g CHO (n=8) .................................................... 53

Incrementai blood glucose area (AUC) of untreated and heat-treated control and fiber test meals (3, 6, and 9g) at 25g CHO (n=8) ................ 54

Incremental blood glucose area (Am) of unaeated and heat-treated control and fiber test meals (3, 6, and 9g) at 50g CHO (n=8) . . . . . . . . . . . . . . . . 54

Correlation between log hardness and AUC of untreated meals at 25g and 5Og CHO levels (n=8) ..................... - ................................. 57

Correlation between log hardness and AUC of heat-treated meals at 25g and 50g CHO Ievels (n=8) ................................................. 57

Blood glucose response of heat-treated control and fiber test meals (3, 6, and 9g) at 25g CHO (n=8) ......................................... 59

Blood glucose response of heat-treated control and fiber test mals (3, 6, and 9g) at 50g CHO (n=8) .............................................. . . 59

Comparison between controls, untreated and heat-treated, at 25g CHO (n=8) . . . . . . . . - . . . . . - . . . . -. . . . . - - - . . . . . -. . . - - - - - . . - - - - . - . - . - - - . . . . . 63

Fig. 3-6.

Fig. 3-7.

Fig. 3-8a.

Fig. 3-8b.

Fig. 3-9

Fig. 3-10

Page

Correlation between log hardness and AUC of al1 heat-treated and untreated meals at 25g and 50g CHO levels (n=8) ................................ 65

Correlation between log hardness and AUC per gram CHO of ail meals(n=8) ...................................................................................... 66

Correlation between fiber-to-nutrient ratio and glycemic index of .................................................... al1 untreated meals (n=8)

Correlation between fiber-to-nutrient ratio and glycemic index of ................................................. al1 heat-treated meals (n=8)

Correlation between psyllium dose and % reduction in AUC per gram psyllium of al1 heat-treated and untreated meals ...................

Correlation between psyllium dose and glycemic index of ail heat- treated and untreated me& .................................................

LIST OF APPENDICES

.............................................................. Appendix I Consent form

Page

Appendix II Study questionnaire ....................................................... 96

LIST OF ABBRlEVIATIONS

%

O C

AUC

BMI

CHO

cm

cm2

CPS

F

Fig

g

hrs

kg

M

min

mL

rnmol/L

rnPa.s

Ns

OZ

P

Pas

psy

SE

sec-'

T

UT

UTM

Percent

Degree Celsius

Incrernental blood glucose area

Body mass index

Carbohydrate

Centimeter

Square centimeter

Centipoise

Femaies

Figure

Gram

Hours

Kilograrns

Males

Minutes

Milli-Liter

Millimole per liter

MiIli-Pascal seconds

Non-significant

Ounce

Poise

Pascal-seconds

Psyllium

Standard error of mean

Reciprocal second

Heat-treated meds

Untreated meals

Universal testing machine

Cbapter 1

INTRODUCTION

AND

LITERATURE REVIEW

1. INTRODUCTION AND LITERA- REVIEW

1.1 Introduction

The ingestion of gel-forming fiber with glucose or a solid meal has been showi to

lower postprandial blood glucose levels in both normal and diabetic individuals (Jenkins et

al., 1978; Holt et al., 1979; Woiever et al., 1979; Williams et al., 1980; Vaaler et al., 1980;

Fussl et al., 1986). Although this relationship had been repeatedly demonstrated in acute

and long-term trials, results remained inconclusive. While some investigators reported

that soluble dietary fiber was effective in attenuating blood glucose response (Jenkins et

al., 1976; Jenkins et al., 1978; Morgan et al., 1979, Uusitupa et al, 1984; Pastors et al.,

199 l), others did not (Groop et al., 1986; Uusitupa et al., 1989; Jais et al., 1984). The

inconsistent results miçht be due partly to the fact that many researchers based their work

only on gravirnetric (quantitative) measurements of dietary fiber, which gave no indication

of its biological function, rather than on rheological measurements.

Dietary fiber is a complex group of non-starch heteropolysaccharides, with different

chemical and physical properties depending on their botanicai origin, handling, processing

and storage. It is believed that rheological properties of dietary fiber such as viscosity and

hydration rate, determined by their physico-chemicai properties, includins structure,

molecuIar weight, particle size and distribution, are the more desirable measurements of

fiber that may indicate their biolo@cal potential (Eastwood and Morris, 1992). Studies

investigating rheoloçical properties of dserent fibers suggested that the ability of fiber to

retard the absorption of glucose in the gastrointestinai tract is a function of their viscosity

(Jenkins et al., 1978). Jenkins et. al. (1978) reported an inverse relationship between

viscosity and glucose response. Using P-Glucan in oats as a model, Wood et al. (1994)

confirmed this relationship by establishing an inverse linear correlation between glycemic

response and log viscosity. In addition, studies reported that reducing or destroying fiber

viscosity by acid hydrolysis resulted in a loss of fiber effectiveness in reducing blood

çlucose levels (Jenkins et al., 1978; Wood et al., 1994). Thus, the importance of viscosity

as an rheological-physiological measure of soluble fiber had been well documented.

However, even when measured appropriately, in vitro fiber viscosity did not always

correlate to the predicted physiological response (O'Connor et al., 198 1). Dilution with

digestive juices and changes in pH along the intestinal tract might be possible factors

contributing to the unpredictable responses (Edwards et al., 1987). Other variables t hat

could affect physiological outcome included fiber and nutrient interaction, method of

administration (Jenkins et al., 2979; Fuessl et al., 1986; Wolever et al., 1991) and meal

type (Gold et al., 1980). Although fiber viscosity is considered one of the better correlates

to its physioloçical effects, more in-depth understanding of its interaction with nutnents

and development of efficient treatment and administration methods are necessary.

In an anempt to investigate the viscosity-physiology relationship and to resolve sorne

of the arnbiguities, a new study model was developed. The effects of fiber and nutrient

interaction and viscosity modification on postprandial blood glucose response was

investiçated by chançing fiber dose and nutrient concentration, along with heat treatrnent

to increase, rather than destroy viscosity. By incorporating the dose and treatment

variables, this study should be able to examine a wide range of viscosity in logarithmic

scale within a single fiber type on physiology, potentially covering the entire range as well.

The approach of this study to expiain the concept of viscosity and physiology is unique in

such a way that we try to bridge the unknown gap between in vitro viscosity measurement

and in vivo physiological response by studying viscosity on the Ievel of interactions

between fiber and nutrients, rather than describing viscosity as a simple numerical

rneasurement .

1.2 Literature Review

1.2.1 Historical Aspects

The role of dietary fiber has been investigated for over a 100 years. At the tum of the

20th century, the concept of dietary fiber and heaith was still not very appealing and only

attracted occasional attention by nutritionists, physiologists and physicians. The interest in

fiber began with the observation of its effects on the bowei. Wheat bran had been shown

to be effective in treating constipation and well-controlled research had proven that fiber

was responsible for the laxative action of wheat bran (Cowgill and Anderson, 1932). It

was not until the early 1960s that the relationship between diet, health and disease becarne

a focus of interest. The work of Keys et. d.(1961), showing that a diet rich in h i t s and

vegetables had cholesterol lowering properties, had been very influentid and supportive of

this diet and disease relationship. During this penod, Trowell, working in East Anica,

observed a very different disease pattern between AGica and the aInuent Western world.

Thirty diseases comrnon in the Western world but rare or even non-existent in Afnca, such

as obesity, diabetes, coronary heart disease, and other gastrointestinal disorders were

depicted in his published book " Non-infectious diseases in M c a " (Trowell, 1960).

Walker, who studied the diets of pnsoners in South &ca suggested that the 'immunity"

of the black population to coronary heart disease might be attributed to the low fat and

high fiber contents of their diet (Walker, 1955). Burkitt, on the other hand, proposed that

appendicitis (Burkitt, 1971) and colorectal cancer (Burkitt, 197 1) were related to diets

low in fiber. Furthemore, study investigating the ciifference in disease patterns of the

descendants of Japanese immigrants to the USA and other populations in North Amenca

found a similar pattern and suggested that lifestyle rather than genetic inhentance was

more important in disease etiology. Since the introduction of western-type diet in 1950,

which typically contained excessive refined sugars and fat while low in fiber, there has

been an increased prevalence of many western diseases in Japan (Oku, 1990). As a result

of these epiderniological observations, it became more convincing that environmental

factors, in particular diet, could account for the differences in disease patterns. A fiber-

deficient diet had been postulated to play a role in the causation of disease while fiber-rich

foods had been considered protective against many of these disorders (Burkitt and

Trowell, 1975).

The dietary fiber hypothesis provoked considerable interest in the general public as well

as in the industrial and scientific cornmunities. Processed and refined foods were

considered undesirable and the flour milling and baking industries were identified as a

major cause of low fiber intake associated with the increased incidence of disease. At the

same time, the hypothesis raised many questions in the nutritionai research community,

with skepticism in the belief of whether the intake or lack of intake of one component,

fiber, could be linked to these diverse physiologicai conditions. Research led to the

realization that fiber, which consists of a complex group of materials in the plant ce11 waii,

had a rmge of chemicai and physical properties that could produce various physiological

effeas. This was the time when more detailed studies of the physico-chemicai properties

of dietary fiber and its components were coosidered necessary. This became a penod of

rapid growth in dietary fiber research, with developrnent in understanding the chernistry

and analysis of carbohydrates, in particular plant cell waU carbohydrates, and in

understanding the physiological role of carbohydrates in foods. A vast number of

experimentai and analytical studies were conducted, with çome focuseci on the physical

and chernicd properties (Brown, 1979) of nber while others looked at the relationship of

specific sources of fiber and pathologicd dwase (BurkiK 1988), physiological funetions

(Salyers et al., 1978) and gastrointemnal properties (Blackburn, 1984).

1.2.2 Definitions and Classification of Dietary Fiber

Dietary fiber is a term that defines a group of substances that share certain chemical

and biologicai properties. The major portion of dietary fiber in foods is derived from plant

ceU walls (Southgate, 1975). There has been a lot of controversy over the years regardhg

the definition of dietary fiber. Dietary fiber had been defineci by Troweli as ali

polysaccharides and lignin in the diet that are not digested by the endogenous secretions of

the human digestive tract (Trowell et ai., 1976). This definition combines physiological,

chemical and analytical points of views. Other t e m recommended by different authors

included plaritix (Spiller, 19751, purifiecl plant fiber (Spiller, 1977), edible fiber (Troweii n

al., 1978), neutral detergent fiber (Van Soest, 1977) and non-starch polysaccharides

(Englyst, 1992). No matter which term or definition is used, one should remember that

substances covered by the general definition may M e r considerably nom each other in

their specific physïological effects.

PIant ceil waiI is a network of cellulose fibrils in a matrix of noncelluiosic

polysaccharides (Lantner, 1968). The detailed composîtion and o r p n h i o n of the plant

cell wall varies with the type of plant group and is characteristic of the species. n ie

matnx polysaccharides include both water-soluble and water-insoluble fractions. Pectins,

arabinogalactans, B-glucan and arabinoxylans are the water-soluble polysaccharides that

are designated pectic substances in the ce1 wail fiaction. The water-insoluble or

hemicellulose fraction includes a range of xylans and xyloglucans (Albenheim, 1965).

Plant foods ais0 contain a range of water-soluble gum and mucilages including

galactomannas and arabinogalactans, etc. Other food components which are associated

with or act like dietary fiber include a range of noncarbohydrate substances such as 1ipi .q

ceii wall proteins, complex lipid matends (nitin, niberin, waxes), inorganic materials

(silica, potassium, calcium and magnesium salts of organic acids). Moreover, a variety of

chemicaily modifieci or synthetic polysaccharides that do not contain a-glucosidic links

and are therefore not hydrolyzed by mammalian digestive enzymes fa11 within the

definition of dietary fiber. Gaiactomamman gums (eg. Guar, Lonin), Algd

polysaccharides (Agar, dginat es, carrageenans), modined cellule ses (ceilulose ethers) and

bacteriai gums O(anthan) are different polysaccharide food additives contributhg to

dîetary fiber.

Fiber cm be generally classifed into two categories based on water solubiiity. Some

soluble fibers, such as pectins, gels, gums and rnudages, fonn viscous gels in water. As a

function of their Wcosity, soluble fibers thicken iuminal contents and slow the rates of

gamic emptyuig and nutrient absorption nom the smaii intestine (Thorne et al., 1983).

Insoluble Bers, on the other hand, are capable of increasing fecai buk, dmeasbg colonic

transit the , and may play an important role in the prevention of bowel disorden mch as

constipation, diverticulitis and hemorrhoids and may be protective against bowel cancer.

Of the two fiber groups, only the water-soluble fibers have been reported to significantly

reduce postprandial blood glucose and insulin concentrations.

1.2.3 Phvsico-Chernical Properties of Dietarv Fiber

It is generally accepted that the physico-chernical properties are of crucial importance

for the functionality and physiological effeas of dietary fibers (Dreher, 1987; Moms,

1992; Thibault, 1992). The characteristic physico-chernical properties of dietary fiber that

are of interest to nutritionists and food chernists include hydration properties such as

swelling, solubility, and water-binding and water-holding capacities; rheological properties

such as viscosity, gelation, and hardness; cation exchange capacity, and particle size.

Depending on the origin, handling, storage and processing of the dietary fiber, physico-

chernical properties are expected to be difFerent.

1.2.3.1 Hvdration Pro~erties

Sweliing and solubility are two closely related properties of polysaccharides. Swelling

is the volume of a given weight of dry fiber f i e r equilibrium has been achieved in excess

solvent (Kuniak et al., 1972). In the process of solubilisation of polyrners, water coming

into the solid spreads the macromolecules (swelling) until they are fuliy extended and

dispersed (Thibault et al., 1992). They then solubilize into random coils. In

polysaccharides, the type of iinkages between sugar residues, such as 1+6 linkages,

induce a chah flexibility and the more flexible, the more soluble is the polysaccharide. In

addition, charge of the polysaccharide is another important factor innuencing solubility .

When dissociated, uronic acid, sulphate or pynivate groups, for example, will tend to repel

polysaccharides ffom each other and thus will favor solubilisation of the polyrners. On the

other hand, solubilisation is affected by pH, the ionic form of the charge, and by the

presence of other solutes such as salts or sugars. Temperature increases solubility of

polysaccharides by breaking the bonds and thus dirninishing the ordered structure.

Water-binding capacity and water-holding capacity (or water absorption) are two

parameters used to describe hydration characteristics. Water-binding capacity is measured

by applying an extemal force to the fiber equilibrated in solvent. The most common

method used is centnfigation. Water-holding capacity relates to the amount of water in

fibers equilibrated in an environment of known water potential, absorbed through

capiilarity, or measured by coliigative methods.

1.2.3.2 Rheolow

Rheology is dehed as 'the study of the change in form and the flow of matter,

embracing elasticity, viscosity, and plasticity" (Brookfield, 1992). in the following

sections, viscosity and hardness, rheological properties of dietary fiber that are of major

interest in relation to physiological effects, wiU be described.

1.2.3.2.1 Viscositv

Viscosity is the measure of the intemal fiction of a fluid, caused by molecular

attraction, which rnakes it resist a tendency to flow (Brooffield, 1992). This fiction (or

resistance of the fluid towards the object applying the force) becomes apparent when a

layer of fluid is made to move in relation to another layer. Therefore, the greater the

friction, the greater the amount of force required to cause this movement called 'bhear",

Shearing occurs whenever the fluid is physically moved or distributed, as in pouring,

spreading, spraying, mixing, etc. Highly viscous fluids, therefore, require more force to

move than less viscous materiais.

Viscosity may be defined as the shear stress divided by shear rate. Shear stress is the

force per unit area required to produce the shearing action. In other words, it is the

resistance between the objea and the fluid and the unit of measurement is dynes per

square centimeter (dynes/cm2). Shear rate is the measure of speed at which the

intermediate layers move with respect to each other, with unit of measure cailed the

'teciprocal second" (sec"). The fundamental unit of viscosity measurement is 'boise" (p),

with one poise or 100 centipoise (cps) defined as a material requiring a shear stress of one

dyne/cm2 to produce a shear rate of one sec". Viscosity rneasurement can also be

expressed in "Pascal-seconds"(Pa.s) or "rnilli-Pascal-seconds" (mPa.s).

OriginalIy, Isacc Newton assumed that at a given temperature, al1 materials have a

viscosity that is dependent of the shear rate. In other words, twice the force would move

the fluid twice as fast. These fluids were known as 'Newtonian fluids" with a linear

relationship between shear stress and shear rate. Typical examples include water and thin

motor oils. However, it was then found out that most fluids did not follow this

relationship and that viscosity was dependent on shear rate. When shear rate is varied in

these so caiied %on-Newtonian fluids': the shear stress does not vary in the same

proportion or even the same direction. Since viscosity of such fluids depends on the shear

rate, experimental parameters of viscometer model, spindle type and speed al1 have an

efect on the rneasured viscosity. For these reasons, the measured viscosity is tenned

'hpparent viscosity" which is accurate only when explicit experimental parameters are

furnished and adhered to. There are several types of non-Newtonian flow behavior,

characterized by the way a fluid's viscosity changes in response to variations in shear rate.

The most common types of non-Newtonian Buids include pseudoplastic (decrease in

viscosity as shear rate increases), dilatant (increase in viscosity as shear rate increases),

and plastic (certain amount of force must be applied before displaying Newtonian,

pseudoplastic or dilatant flow charactenstics).

The process of viscosity development in solution involves several steps. Initiaily, in

contact with water, soluble polysaccharides, including fiber panicles, swell as water

molecules diffise through the fiber surfaces into the denser environment. Typically, at a

critical point, depending on the fiber hydration rate, fiber sacs nipture and release fiber

molecular coils due to an enlargement of pores on the surface of the sacs and an increased

in coi1 mobility. These fiber coils are capable of interacting with one another and with the

surroundhg nutrients. When segments of fiber mo1ecules in solution collide, they form

multiple associations over several chah units. Due to the great length of molecules and

their inherent coiling, flexing and entanglement characteristics, fiber molecules may not

bind in perfectly regular associations, with only specinc regions called junaion zones

where molecules fit and associate together (Whistler, 1993). The stabüity of the junction

zones formed between molecules depend mainly on its length, that is, the number of

intermolecular bonds that develop. These bonds are of various kinds, with hydrogen

bonds contributhg the major associative forces. The process of random junction zone

formation between different molecules continue until many, if not most, of the molecules

become involved in a three-dimensional network. As disordered molecular chahs become

associated and form ordered junction zones, the network of the viscous solution or gel is

strengthened (Moms, 1995).

Viscosity can be measured by different apparatus, with Brookfield Viscometer being

one of the most commonly used. Brookfield viscorneter is of the rotational variety which

measures the torque required to rotate the spindle in the fluid (Brooffield 1992). A

number of factors affects the measurements of viscosity. These include temperature, shear

rate, measuring conditions, time, and fluid composition. Temperature is one of the most

obvious factors that can have an effect on the rheological behavior of a materiai since

some materials are quite sensitive to temperature. A relatively small variation will result in

a significant change in viscosity. Some polysaccharide solutions, such as psyllium

solutions, are very sensitive to temperature change. As mentioned before, shear rate is a

very important factor determinhg the viscosity measurement of non-Newtonian solutions.

Measuring conditions, nich as Viscometer mode, spindle size and speed combination,

sample container size, and sample preparation techniques, ali affect the accuracy as well as

the actual viscosity of the materid. Some fluids will display a change in viscosity with

tirne under conditions of constant shear rate. Thkotropic and rheopectic are two

categones of this type of fluid. Finaîiy, the composition of a material is a determining

factor of its viscosity. When composition is altered, a change in viscosity is quite likely.

1.2.3.2.2 Hardness

Hardness is defined as the force necessary to effect a given deformation (Penfield et al.,

1990). In other words, the harder the sample, the more force is required to compress the

sample to a certain distance. The Instron Universal Testing Machine (UTM) is comrnonly

used for texture profile analysis of food. The crosshead with a specific attachent of the

UTM moves up or down at a constant rate of speed. As it rnoves, the force that is

required to compress a sample of food is continuously recorded as a curve. Hardness is

the peak height of the curve at maximum compression. Other textural pararneters, such as

co hesiveness, adhesiveness, springiness, gurnminess and chewiness, c m be interpreted

using information such as the area under the curve.

1.2.4 Dietarv Fiber and Disease

Considerable interest in dietary fiber began when Burkitt and Trowell (1972)

hypothesized that diabetes and heart disease were fiber deficiency disorders. Diabetes,

both insulin-dependent and noninsulin-dependent, is a disease resulting fiom a relative

deficiency of insuiin, with diet being one of the chief modes of treatment. Over the years,

the recommended diabetic diet has changed ftom a high fat, low carbohydrate, to a high

carbohydrate, low fat diet (CD4 1981; BDA, 1982; ADA, 1987) in order to decrease the

nsk of cardiovascular disease which is the major cause of death of diabetic patients

(Kannel and McGee, 1979; Keen and Jarret, 1979). Although the proportion of

carbohydrate in diet has been recommended to increase? its effect on metabolisrn is stili

unclear. Glucose tolerance (Brunzell et al., 1971) and in& sensitivity (HUnsworth,

193 5) increased on a high-carbohydrate diet. Later, West and Kalbfleisch (197 1) showed

an inverse association between carbohydrate consumption and the prevalence of diabetes.

On the other hand, there was evidence that the energy density of carbohydrates was

positively associated with the 4-year risk of glucose intolerance (Feskens et al., 1991).

This contradiction has been resolved by studies which show that the intake of different

carbohydrate foods results in different glycernic responses (Jenkins et al., 1977; Crapo et

al., 1977; Bantie et al., 1983; Ienkins et al., 1988) and that the intake of starch and

polysaccharides is beneficial, partly due to an increase in dietary fiber intake (Trowell,

1975).

Dietary fiber and high fiber foods are believed to affect carbohydrate metabolism by

reducing the rate of carbohydrate absorption and by increasing colonic fermentation

(Wolever, 1995). A number of pieces of evidence suggest that slowing the rate of nutrient

absorption influences and improves systemic metabolism. A direct relationship between

the ability of punfied dietary fibers to slow the diffusion of glucose out of dialysis sacs in

vitro and their blood glucose and insulin lowering abilities had been demonstrated (Jenkins

et al., 1986). It is also show that the rates of digestion of foods in vitro are related to

their blood glucose (O'Dea et al., 1981; Jenkins et al., 1982; Brand et al., 1985; Thorbum

et al., 1987; Bornet et al., 1987) and insulin responses (Bomet et al., 1987; Wolever et al.,

1988). In addition, it had been pointed out that rapidly absorbed glucose produced

greater glycernia and glucosuna in diabetic subjects compared to slowly absorbed

carbohydrate in the form of aarch (Ailen, 1920). Thus, foods which are slowly digested

reduce acute blood glucose responses and may improve blood glucose and lipid control in

diabetic patients.

Consumption of fiber, both in food or as supplements, has been dernonstrated in acute

studies to reduce postprandial hyperglycemia in normal (Jenkins et al., 1977; Potter et al.,

1981; Thorne et ai., 1983) and diabetic patients (Jenkins et al., 1978; Goulder et al., 1978;

Ebeling et ai., 1988). The most effective fiber sources were the soluble types with the

greatest Mscosity and the fiber had to be incorporated into the food in order to have

metabolic impact (Jenkins et al., 1979a). Viscous fibers such as guar (Jenkins et al., 1978;

Wolever et ai., 1979; Edwards et ai., 1987), pectin (Holt et al., 1979; Gold et al., 1980),

psyllium (Jarjis et al., 1984; Wolever et al., 1993) konjacmannan (Ebihara et al., 198 l),

xanthan (Edward et al., 1987) and others have been shown more consistently to flatten

posptrandial blood glucose and insulin responses in single test meals, while the effect of

nonviscous fiber such as wheat bran and cellulose appears more variable (Jefferys et al.,

1974; Harnberg et al., 1989). In long term trials, consumption of high carbohydrate diets

containing a mixture of soluble and insoluble fiber has been shown to improve glucose

tolerance and reduce serum cholesterol and triglycendes in normals (Jenkins et ai., 1975;

Albrink et al., 1979), diabetics (Kay et al., 198 1; Simpson et al., 198 1; Anderson and

Ward, 1982; Riccardi et ai., 1984; Hagander et al., 1988), and hypertriglycendernics

(Anderson et al., 1980). Similady, the improvements in glycemic and lipid controls were

larger and more consistent with the use of viscous rather than nonviscous fibers @oi et

al., 1979; Glatti et ai., 1984; Osilesi et al., 1985). A meta-analysis comparing the effect of

guar and nonviscous fibers showed that guar reduced urinary glucose by 41% (p<0.00 L),

fasting blood glucose by 1 1% (p<O.OOl), and glycosylated hemoglobin by 5% (p<0.01) in

18 studies; while nonviscous fibers increased unnary glucose by 34%, reduced fasting

blood glucose by 3.8% (pC0.02) and glycosylated hemogiobin by 3.4% (ns) in seven

studies (Wolever et al., 1993).

1.2.5 The Mechanism of Action of Dietarv Fiber on Carbohvdrate Metabolism

The mechanism by which soluble fiber lowers acute plasma glucose concentrations and

improves long-tenn glycemic control appears to be related to its ability to alter events

occumng within the gastrointestinal tract. Blood glucose concentrations are affected by

several factors, including the rate of gastnc emptying, digestion, intestinal absorption, and

the rate of metabolism once glucose is absorbed. Soluble fiber seerns to slow absorption

of carbohydrates by (a) delaying gastric emptying, @) altering enzyme-substrate

interactions and small intestine motility, (c) poor mking of lumenal digesta in the gut and

(d) slower diffusion f?om the gut to the epithelial cells due to an increase in unstirred

water layer. Studies have show that rnixing large doses of viscous fiber with liquid

carbohydrate meals prolonged gastnc emptyuig (Blackburn et al., 1984; Torsdottir et al.,

L989), while solid meals showed more variable results (Sandhu et ai., 1987; Rydning et al.,

1985). However, since correlation between the change in blood glucose response and

gastric emptying rate of viscous fibers was not found (Ray et ai., 1983; Flourie et ai.,

1985; Edwards 1987 ), mechanisms other than delayed gastric emptying, such as reduction

of enzyme-substrate interaction, diffusion and absorption rates might play a more

important role in decreasing postprandial glycemia. Viscous soluble fiber has been s h o w

to inhibit the aaivities of pancreatic amylase (Dunaif et al., 198 1; Isaksson et al., 1982) by

reducing enzyme-substrate contact. Evidence has dso been shown diat viscous fibers can

infiueoce accessibility of available carbohydrates to the mucosal surface by reducing

luminal mbchg and slow their absorption Results from in-vitro dialysis expenments

demonstrated that viscous fibers reduced solute movement (Blackburn et al., 1984) and

therefore, be responsible for inhibiting glucose uptake. Soluble fiber may infiuence

small intestinal tbsorption of carbohydrates by delaying transit tirne (lenkins et ai., 1978).

The chronic effect of fiber on carbohydrate metabolism may be related not only to the

acute interaction of fiber and food in the gut but also to subsequent alterations in

metabolism and/or aiirnentary stmcnire and function (Floune, 1992). Chronic intake of

fiber may alter hepatic glucose metabolism and enhance tissue sensitivity to insulin.

Adaptive changes in intestinal structure and funaion may also occur and influence

digestion and absorption of carbohydrate. There was evidence of delayed ganric emptying

&er chronic pectin supplementation in diabetics (Schwartz et al., 1984). Changes in

pancreatic secretion output and activity (Ikegani et al., 1990) and modification in intestinal

length and weight, and morphology of mucosa, c d turnover and mucus secretion (Sigleo

1984; Vahounv, 1987) were also possible afier chronic intake of dietary fiber.

Psyllium, a soluble fiber denved fiom plants of the Plantago genus (ispaghula, isabjui,

fleawort) which grow in certain sub-tropical regions, is indigestible and nonabsorbable in

humans. Ground seed husk is commody used as the source for psyuium since the active

ingredient, the seed gum, is located primarily in the seed husk. Psyllium is rich in mucilage

(a hemiceilulose) and is composed of highiy branched arabino-xylan. The structure of

psyllium, proposed by Sandhu et al. (1981), consists of a backbone of P-D-xylopyranosyl

units linked (1+ 4) and (1- 3) (ratio 13:3) w-th oniy the 0-4 substituted units bearing

side chains. The side chains consist of a-L-arabinofuranosyl units linked (1+ 3) and (1+

2) (ratio 4: 1 ) and P-D -xyIopyranosyl units linked (1 + 3) and (1 + 2) (ratio 4: l), and a-

D-Gal&-(1- 2)u-L Rha, aldobiouronic acid units linked ( l - t 2) to the main. Gum

composition and structure dzer between different species of psyllium.

Purified psyllium seed gum is a white, fibrous matend that hydrates slowly to form

viscous dispersions at concentrations up to 1% (BeMilier, 1973). At 2%, a clear,

gelatinous solid mass is formed with clear dispersions. Psyllium seed gum dispersions are

thixotropic. Heat increases the initial viscosity of gum dispersions (Mattha, 1977); while

changes in pH (range 2 to IO), or addition of sodium chloride, do not affect viscosity

(BeMiller, 1973). However, gels fomed from psyllium gum dispersions are unstable at

higher pH values (Mattha, 1977). On the other hand, both nscosity and thixotropy are

increased by the addition of sugars; while the effea of electrolytes varied (Mattha, 1977).

Mucilages formed from psyllium seed have been used since ancient times, both in home

remedies and in the practice of medicine (BeMiUer, 1993). Psyllium is also widely used in

food industry. It has been incorporated into food products including cookies, ice-cream,

sugars, oiis, baked goods, and ready-to-eat cereai (Chan et al., 1988). Psyllium has shown

a range of metabolic effects. It is widely used as an active ingredient in laxatives to

prevent or treat chronic bowel disorders such as constipation, diverticular diseases and

imtable bowel syndrome due to its potent fecal bulking effect (Eastwood et ai, 1978; Pnor

et al., 1987), usually ascribed to insoluble fibers. Compared to wheat bran, psyllium had a

more pronounced action on the amount of water in the stools and the total stool mass

(Smith et al., 1980). The water-retaining properties of psyllium gum may cause a feeling

of fùllness or satiety that depresses appetite and causes weight loss (Russ et al., 1985).

Besides laxative pro perties, psyllium-enriched diets have also been shown to be effective

in lowering cholesterol levels in hypercholesterolemic patients (Anderson et al., 1988; Bell

et al., 1989; Levin et ai., 1990) and reducing glucose and insulin concentrations in normal

(Jarjis et ai., 1984) as well as diabetic individuals (Florholmen et al., 1982; Pastors et al.,

199 2).

Among different soluble fibers, psyllium is considered relatively palatable, inexpensive,

and has a long hiaory of safe use. However, when compared to some other soluble fibers,

viscosity level of psyiiium is considered at the lower end. In one preliminary study done in

Our laboratory, the relationship between viscosity levels and physiological responses of

three soluble fibers, Konjacmannan, Xanthan, and P syiiium, was investigated. Psyllium

(2,200 cps) was the lowest in viscosity level when compared to xanthan (6,300 cps) and

konjacmannan (12,000 cps) (2%, shear 30 sec", 2S°C, spindle F) and the least effective in

reducing glucose response. Therefore, psyliium would be a good source of viscous fiber

to be studied since a large margin of increase in viscosity is possible.

1.2.7 Uncertain Aspects of Soluble Fibers

Soluble dietary fiber has been recognized for its blood glucose, insulin and Iipid

lowering effects. However, studies investigating this phenornenon did not corne to a

conclusive statement that soluble fiber, even of the same type, produced sunilar

physiological effects. Table 1-1 showed the percent glucose and insuiin changes of a

number of dEerent studies, al1 examining the effect of supplementing guar gum to 50g

carbohydrate glucose meals in normal subjects. Renilts showed a large range in percent

glucose reduction (from -27% to -68%) d e r giving the same quantity of guar (14.5 g).

Figure 1-1 graphicaliy demonstrateci the results obtained fiom £ive studies. A non-

sipfïcant correlation ( ~ 4 . 5 9 , n=8, p=û.1243) between grams of guar adrninistered and

percent change in glucose was found. Similarly, table 1-2 listed the results of the midies

examining the effect of supplementing pectin and psyliium to SOg carbohydrate glucose

meals in normal indivîduals. In the case of pectin, supplying 14.5 grams of fiber in two

dEerent midies resulted in a huge dzerence in percent glucose change (-1 1% versus -

55%). Whereas, in one study, doublhg the quantiq of psyllium (3. Sg to 7g) not oniy had

no irnprovement in glucose reduction; in contrast, adding more psyKurn produced a less

favorable renilt (3 Sg: -33% and 7g: -12%).

One of the many possible reasons for this inconciusive observation is subject variability,

with Înd~dual differeace in response to fiber. Another more si@cant reason may be

that moa of these studies did not examine the physico-chemicd properties of dietary fiber,

which provide beîter information about their physiological e E i . Ditferent sources of

the same polysaccharide, under the same family name, can show great variation in their

Table 1.1 Effect of adding guar gum to 5Og CHO glucose meals on acute blood glucose and insulin responses in normal subjects. Data obtained from Wolever & Jenkins, CRC Handbook of DF in Human Nutrition, znd ed., chapter 4.1, 1993.

Guar (g) % Change in % Change in Reference Glucose Insulin

2.5 - 24 (ns) - 64 Edwards CA, 1987

2.5 - 34 - 65 Jaris HA, 1984

0 (ns) - 44 O'Connor N, 198 1

- 66 Morgan LM, 1985

9.0 - 23 O'Connor N, 198 1

14.5 - 50 - 54 Jais HA, 1984

14.5 - 38 - 60 Blackburn NA, 1984

14.5 - 27 Jenkins DJA, 2 979

14.5 * 0 (ns) Jenkins DJA, 1979

14.5 - 68 - 58 Jenkins DJA, 1978 - - - - - --

15.0 * - 2 (ns) + 28 (ns) Walquist ML, 1979

* - Glucose was taken &er par . - These data are not included in the correlation shown in figure 1-1.

Ns - Results not statistically significant @ > 0.05) Lack of a figure means that the data is not available

O 5 1 O 15 20

Grarns of p a r administered

Figure 1-1. Correlation between % glucose reduction and gram of guar

addstered in five acute studies.

Table 1-2. Effects of adding Pectin and Psyllium to 50s CHO glucose meals on acute blood glucose and insulin responses in normal subjects.

Fiber Fiber (g) % Change in % Change in Reference Glucose Insulin

Pectin 14.5 - i i(ns) - 2 (ns) Jenkins DJA, 1978

14.5 - 55 Holt S, 1979

Psyllium 3.5 - 33 (ns) - 39 (ns) Jaris Hq 198 1

7 - 12 (ns) - 28 (ns) Jaris HA, 1981

Ns - Results not statistically significant (p > 0.05) Lack of a figure means that the data is not available

physical properties (EUis et al., 1986) and physiologicai effects (Roberts et al., 1989).

Instead, measurement of rheological property such as viscosity has been shown to be

related to the abaity of various purified fibers to flatten blood glucose and insulin

responses in human subjects (lenkins et al., 1978; Edwards et ai., 1987). Most

investigators do not measure viscosity Ievels of their test fibers. When measured, the data

often cannot be compared because of different measuring conditions such as different fiber

concentrations, different techniques and different viscosity units. Thus, efforts should be

put into understanding the rheologicai properties of the fiber material, tested under

standard conditions, before adrninistered in clinical trials.

Another uncenainty is regarding the implication of viscosity measurement. Viscosity is

considered an usehl parameter in predicting physiological response. However, viscosity

measured in vitro does not always correlate with in vivo response (Edwards et ai., 1987).

Dilutions with digestive juices and changes in pH almg the gastrointestinal tract, as *

demonstrated by an in vitro model, can produce marked reductions in viscosity in some

polysaccharides (Morris, 1986; Edwards et al., 1987). In other words, some soluble fibers

can maintain their initial viscosity whiie others do not. In addition, some soluble

polysaccharides form solutions that are non-Newtonian in nature, with their viscosity

varies according to the shear rate to which they are subjected to. Therefore, in order to

predict the eEect of a polysaccharide in the gut, it is necessary to accurately estimate the

shear rate in the gastrointesthai tract.

Another consideration is the d ~ c u l t y in measuring the viscosity of gastrointeninai

contents in humans, which may provide a better correlate to the observed physiologicai

response. In the present tirne, due to ethicai reasons, this approach is only conducted in

animal mode1 (Ellis et al., 1995) and ileostomic patients. There is also very little insight

into the effects of whole food on rheology in vitro and in the gut. Since gastrointestinal

contents during the process of digestion are not homogenous, with lumps appearing

throughout (Read and Eastwood, 1992), it may be quite difficult to get a viscosity

measurement that is representative of the sample. It is necessary to develop and validate

a rnethod for measuring the rheological properties of whole food and gastro-intestinal

contents.

There are a number of unresolved issues with the use of viscosity measurement in

relation to physiological effects of soluble fiber. Thus, there is a need to elucidate these

issues by studying viscosity from another angle, possibly by looking at how fiber and

nutrient molecules interact dunng the process of viscosity development. It is not

appropriate to consider viscosity rneasurement as a single numbet in predicting

physiologicai response, since numerous other variables may cause different results in

different samples, which may not be comparable anymore.

1.3 Hypothesis and Objectives

1.3.1 Research auestions

Does increase viscosity by increasing fiber dose and heat treatment proportionally

reduces postprandial blood glucose response? 1s viscosity the only factor, or are there

other elements besides viscosity, such as fiber-and-nutnent ratio, which rnay play an

important role in detennining postprandial blood glucose response?

1.3.2 bwothesis

Postprandial blood glucose response to dietas, fiber-containing meals, is inversely

correlated to its viscosity, which can be modified by fiber dose and heat treatment. In

addition to and independent of viscosity, fiber-to-nutnent ratio may also be an important

factor in predicting blood ducose response.

1.3.3 Objectives

The overall objective of this study was to investigate the effects of fiber viscosity and

its interaction with nutrient on postprandial blood glucose response.

In vitro experiment :

1. To develop a study mode1 covenng a wide range of viscosity levels with a single fiber

type by modifjing fiber dose and treatment methods.

2. To determine the optimal process to maximize fiber viscosity.

3. To determine the viscosity and hardness levels of ail experimentai samples.

In vivo experiment :

1 . To study the effect of modifying meal viscosity of a single fiber type by varying fiber

dose and treatment met hods on postprandial blood glucose response.

2. To detennine the interaction between fiber and nutnent molecules dunng viscosity

development and how this relates to the changes in postprandial blood glucose

response.

Chapter 2

IN VITRO MEASUREMENTS :

EFFECTS OF FIBER DOSE AND PROCESSING METHODS

ON RHEOLOGY

2. IN VITRO MEASUREMENTS :

EFFECTS OF FIlBER DOSE AM) PROCESSING METHODS ON RHEOLOGY

2.1 Introduction

The main objective of this study was to investigate the physiologicai effect of fiber-

supplernented meals covering a wide range of viscosity levels, fiom very low with low

dose and without processing, to very high with high dose and after heat treatment.

Therefore, it was necessary to determine the effects of fiber dose and various processing

methods on viscosity before testing in human subjects. In particular, the rationales for

conducting these experiments were to determine meai viscosity at different fiber

concentrations and the optimal way of processing to rnaximize fiber Mscosity. The effects

of heat, stimng and air interaction in sample preparation, and the effects of re-heating and

storage of heat-treated sarnples on viscosity would be investigated. Viscosity and

hardness measurements were performed for cornparison between test samples.

2.2 Materials and Methods

AU sarnples for rheologicai testing were prepared in the laboratory at University of

Toronto 24 hours before measurement. The Uigredients were measured pnor to mixing.

A graduated cyiinder (Pyrex, No.3022, 100rnL) was used to measure the quantity of liquid

while an electronic digital scale with two decimal places (Mettler PM 6000) was used to

measure the weight of fiber.

2.2.1 Meal com~osition

Control samples of two nutrient levels (25g CHO and 50g CHO) were prepared. The

25g CHO control sample consisted of lOOmL glucose solution (Glucodex, Rougier Inc.)

and 200m.L distilled water, while the 50g CHO control sample containeci 200mL glucose

solution and lOOmL distillecl water. Total meal volume was standardized to 300mL. For

fiber test samples, psyiliurn @ h a g o ovukz, 98% seed husk, Trade Technocrats, Toronto)

of either 3g (1% concentration), 6g (2%), or 9g (3%) was added to each of the 300mL

control samples. Pnor to rheological meanirement, sarnples were either untreated or heat-

treated. Composition of al1 experimentai samples was liaed in table 2-1.

2.2.2 Pre~aration method for the untreated samnles

Test samples consisted of the pre-weighted fiber and 300mL glucosdwater solution

were mixed thoroughiy with a Fisher magnetic stirrer in 500mL glass beakers (Pyrex) at

room temperature (23OC) for ten minutes to ensure complete distribution and to avoid

clumping of fiber. M e r initiai stimng, uimples were left at room temperature for three

hours with light mixing every 15 minutes throughout the penod by inverting the beakers

several times to obtain consistent and smooth textures. Samples were then stored in the

ref?ïgerator @ O C ) ovemight before meaniring the next day, 24 h o m af'ter initial mixing-

Table 2-1. Composition of experimental meal samples.

Experimental Meal Samples

(8eat-heated or Untreated)

Nutrient Level Water Level PsyUium Dose (g)

Glucose (mL) (mL) CHO (g) Controls Fi ber Meals

200 mL Glu. (25 g CHO)

200 mL Glu. (50 g CHO)

+ A total of 16 experimental meal samples were prepared and subsequently tested with human subjects.

2.2.3 Pre~aration method for the heat-treated sam~les: effect of different

processing methods on viscosity

2.2.3.1 The effects of stirrinn and air interaction durinn heat in~ and cooline on viscositv

Each sarnple consisted of 3g psyllium, lOOmL glucose solution and 200mL distilied

water. An aluminum cooking pot was used for heating samples on the aove top. The

mixture of glucose and water solution was first heated in the pot until boiling (10o0C).

Psyllium powder (3g) was poured into the boiling solution and the mixture was initially

stirred with a spoon and was heated for an additional ten minutes. In order to determine

the optimal method to maximire viscosity, dEerent combinations of heating, mUang and

cooling procedures were conducted. Table 2-2 lists the six dEerent tests (A to F).

During the ten-minute heating phase, the mixture was heated either with no additional

aimng or mWng (samples A and D), with constant stirring but without lifting to get in

contact with air (samples B and E), or with constant stirring and part of the mixture raised

with a spoon into the air every three rounds of aimng (samples C and F). M e r ten

minutes, hot mixtures were transfemed into standard glas bowls. The mixtures were

cooled d o m either with no additional mixing or stirrîng (samples A, B and C), or with

stimng every five minutes for 15 seconds during the three hours (samples D, E and F).

Changes in viscosity of ail samples were determined Msually and independently by

three observers. Viscosity rating was based on a scale of one to ten, with one indicating

low and five indicating medium viscosity and ten representing highly viscous solution or

fimi gel. Samples were evaluated 24 houn after preparation.

Table 2-2. Combination of different procedures in tests to determine the optimal viscosity level.

- -

Test sample Heating Cooling

StUTing without lifting No stining

Stimng with lifting No stimng

No stirring S tirring

Stirring without lifting Stirring

F Stirring with lifting Stirring

2.2.3.2 The effect of re-heatinn of the heat-treated sam~les on viscositv

The effect of re-heating on viscosiv of d l heat-treated samples (A to F) was

determined 24 hours afler preparation. Each of the samples was transferred back to the

alurninum pot and was reheated to 100°C. Changes in the structure and texture of the

samples were observed and rated.

2.2.3.3 The effect of storine tirne of the heat-treated samales on viscositv

The effect of storing time on the stability of heat-treated sarnples was examined seven

days afler preparation. Samples were covered with plastic wraps and stored in the

refngerator at 4°C for seven days before observations and ratings regarding the structural

and textural changes which took place.

2.2.4 Viscositv measurement

Apparent viscosity of the control and fiber samples was determined by the Brookfield

Synchrol-lectric viscometer (mode1 LVT, spindle F). Prior to measurements, a reading of

zero revolutions per minute fiom the viscometer was obtained to ensure proper

positioning and leveling of the viscometer. The viscometer was then calibrated using a

standard solution of 5 100 centipoise. Samples were placed directly under the spindle head

at a fixed starting level. The motor was then tumed on so that the spindle head could

move slowly up and d o m the sample, allowing it to measure viscosity at different points.

Viscosity dia1 readings were obtained at shear rates 6, 12, 30 and 60 revolutions per

minute at 30 and 60 seconds. Readings were then converted mathernatically by

multiplying a factor, dependent on the shear rate and spindle size, and was presented in

"centipoise" .

2.2.5 Eardness measurement

Since viscosity of the heat-treated samples could not be obtained fiom the Brookfield

viscometer (reading over 100 on scale using the smallest spindle), the instron Universai

Testing Machine (Instron UTM, mode1 1 132) was used to provide rheological information

of the highly viscous samples. Ail samples with lower levels of viscosity measurable by

the Brookfield viscometer were also tested by the Instron UTM to allow for cornparison

between the two methods. Samples of the sarne quantity were transferred to 3.25 oz small

plastic containers (Solo Cup Co.). The Instron was calibrated according to the

instructions provided with the recording pen resting at zero. Samples were placed one at

a time on the testing area which had been set at a specific height. As the test button was

pushed, the cylinder-shaped compression anvil slowly lowered to compress the sample; the

force used to compress was recorded as a function of deformation. The peak of the curve

is considered the hardness of the sarnple which is proportionai to the amount of force

needed to compress the sample a certain distance.

2.3 Results

2.3.1 Pre~aration method for the heat-treated sam~les: effect of different

processinp. methods on viscositv

Table 2-3 showed the observationai viscosity ratings of al1 heat-treated samples fiom

experiments (a), (b) and (c), evaluated visually and independently by three individuals .

Table 2-3. Observational results of the heat-treated samples 24 hours after heat treatment, during re-heating, and 7 days after initial heat treatment.

Sample Heating Cooling Viscosity Ratings (0-10) ' (10 minutes) (3 hours) (Mean f SE)

After heat- During After treatment re-heating storage (24 hours) (7days)

No stimng No stimng 3.5 + 0.4 1 .O k 0.0 3.5 1: 0.3

Stimng wihout lifting NO stimng 7.0 k 0.4 1 .O f 0.0 7.0 t O S

Stimng with lifting No stimng 8.0 + 0.6 1 .O L 0.0 8.0 + 0.4

No stimng Stirring 2.5 f 0.5 1 .O + 0.0 2.5 3- 0.3

S timng Without[ifting Sfimng 3.6k0.4 1.0 f 0.1 3 -5 k 0.5

Stirring with lifting Stirrbg 4.0k0.3 1.0 10.0 4.0 t 0.4

Visual viscosity rating was based on a scale of 1-10, with 1 indicating low viscosity, 5 medium viscosity and 10 representing a high viscosity solution or h n gel. Results are based on judgments fiom 3 individuais. Heat-treated samples were evaiuated 24 hours after preparation; re-heated samples were evaluated during re-heating while stored samples were examined 7 days &er initial preparation.

2.3.1.1 The effects of stirrinp and air interaction dur in^ heatin~ and cooline on viscositv

Samples prepared by different treatment methods were different in their homogeneity

by appearance. Samples A and D, with no stirring dunng heating process, ended up as

two-separate-phase mumires after cooling, with a concentrated fiber phase on top and a

liquid phase on the bottom. Of ail the treatment methods, samples B and C, with stimng

during heating while left alone during cooling, were the firmest samples produced. A

slight but not significant difference in gel strength between samples B and C was seen,

indicating that mixing with constant interaction with air (lifting part of the sample into the

air) dunng heating resulted in a small increase in viscosity when compared to mking in

heat alone. Small chunks of semi-solid gelation products were seen while heating samples

B, C, E and F. Stimng during cooling broke the 2 diaina phases of sample D which

ended up as a heterogenic solution with fibers chunks dispersing throughout. In addition,

stirring during cooling did not d o w formation of strong bonds associated between fiber

and nutnent developed from the process of heating in samples D, E, and F. The result was

a weaker gel sirnilar to the untreated samples prepared at room temperature. Therefore,

stirring during cooling was not an appropriate method to increase viscosity of samples. It

was concluded from this experiment that stirring of sample during heating with air

interaction and coohg without stirring was the optimal method to produce sample with

maximum viscosity. This would be the method of preparing heat-treated test meals for

physiological testing.

2.3.1.2 The effect of re-heatine of the heat-treated samples on viscositv

Re-heating liquefied al1 the previously heat-treated samples (A to F) (Table 2-3). As

the reheated liquid samples were left to cool down at room temperature, the process of gel

formation started again. Thus, the formation of viscosity and gel network is reversible by

heating and cooling treatments.

2.3.1.3 The effect of storine time of the heat-treated samales on viscositv

There was no major structural or texturai change observed visually in any of the heat-

treated samples after being stored in the refngerator for seven days. The effect of gel

syneresis, commonly seen with gels as the gel network structure tightens and water

exuded from the gel, was not observed with psyilium gel. Thus, heat-treated psyllium gel

was considered a stable gel at 4°C after seven days of storage.

2.3.2 Viscositv measurement of untreated samdes

Viscosity of ail untreated samples were measured 24 hours after preparation.

Measurements were taken at shear rates of 6, 12, 30, and 60 sec*'. Apparent viscosity

measurements of the 25g and 50g CHO untreated samples were shown in Table 2-4 and 2-

5 respectively. Results presented are the rneao++SE of 3 measurements. At each shear

rate, fiber dose was iinearly correlated with apparent viscosity (i.e. 30 sec*' :

Mscosity=12 13.3 xfiber dose-4697.6, r=0.95, p=O.OO3 9) (Figure 2-1). Although prepared

at the sarne fiber concentration, a slight but non-significant (~4.955) viscosity ciifference

between samples of two nutrient levels was found.

Table 2-4. Apparent viscosity measurements of ail 25g CHO untreated fiber samples at different shear rates, 24 houn after initial mixing.

-- - - - - . -. -

Psyiiium Dose (g) Apparent Viscoaity (cps)

6 sec" 12 sec-' 30 sec-' 60 secsL

Table 2-5. Apparent viscosity measurements of al1 5Og CHO untreated fiber samples at different shear rates, 24 houm after initial mixing.

Psyllium Dose (g) Apparent Viscosity (cps)

6 sec-' 12 sec-' 30 sec-' 60 sec-'

259 CHO

6

Psyiiium Dose (gram)

Figure 2-1. Correlation between psyliium dose (3,6, and 9g) and apparent viscosity (shear : 30sec-1) of 25g and 50g CHO untreated meals

Viscosity = 1213.3 X dose - 4697.6. Insimcant difference (p=0.955) between 25g and 50g CHO levels was observed.

2.3.3 Hardness measurements of al1 samoles

Hardness of the untreated samples (Table 2-6) was highly correlated with fiber dose

(hardness==.2xfiberdose+I. 7, ~0.99, p=O.OOS6) (Figure 2-2). Similarly, hardness of the

heat treated samples (Table 2-6) was also significantly correlated with fiber dose

(hardness= 10 1 -7xfiberdose-306.7, r=0.97, p=0.043) (Figure 2-2). When comparing

between the hardness of the untreated and the heat-treated samples, the difference in

hardness was relatively smd between the two at the Iow fiber dose (3g: 2.7 times

difference); however, as fiber dose increased, the difference in hardness increased

considerably (6g: 8.8 times and 9g: 16.3 tirnes dEerence). Significant difference in

hardness between heat-treated and untreated samples was found (p=0.0002) when

analyzing results including al1 three fiber doses. Almoa identical result s were obtained

fiom samples of the same fiber concentration at both 25g CHO and 50g CHO levels. The

Instron LTTS was reliabie and results were precise and highly reproducible. Results shown

in Table 2-6 and Figure 2-2 were identical in 3 separate measurements.

2.3.4 Correlation between viscositv and hardness measurements

A strong linear correlation between viscosity and hardness was observed from the

measurements of the untreated fiber samples (Viscosity=-280.3 x hardness-4623 -7, rO.98,

p=0.0034) (Figure 2-3). As viscosity measurement could not be obtained nom the heat-

treated fiber samples, hardness measurernents of these samples would be used to indicate

the relative levels of viscosity.

Table 2-6. Hardness measurements of ail untreated and heat-treated samples at 25g and 50g CHO, 24 hours after initial mixing.

--

Psyllium Dose (g) Hardness (gram~)

Untreated samples Heat-treated samples

25g CHO 50g CHO 25g CHO 5Og CHO

Q Unfreafed Y = 4.2 X + 1.7 R = 0.99 p = 0.0056

Treated Y= 101.7 X - 306.7 R = 0.97 p = 0.043

Psyliium Dose (gram)

Figure 2-2. Correlation between psyüium dose (3,6, and 9g) and hardness of 25g and 50g CHO heat-treated and untreated meals

Hardness = 4.2 X dose + 1.7 (untreated) Hardness = 10 1.7 X dose -306.7 (heat treated)

Aimost identicai results were obtained fiom heat-treated and untreated samples

Figure 2-3. Correlation between hardness and apparent viscosity (shear: 3ûsec-1) of 25g CHO nntreated meals at dinerent psyiiiam doses

Viiosity = 280.3 X hardness - 4623.7

2.4 Discussion

The goal of these experiments was to develop a wide viscosity range of psyllium

samples by modifluig psyUium dose and by the application of heat ueatment. Renilts

nom the rheological meaniremefis confimieci that psy&um dose was directly proportional

to viscosity and hardness Iwels, while with heat treatment, hardness (viscosity) Iwels

codd be increased significantly. Hardness of samples, ranging from 5.0 g to 650.0 g, was

obtained by combining the two variables.

During the process of viscosity developmem, the ment to which random junction

zones fom varies, depending on a number of factors including the availability, active level

and nrength of fiber molecuies, the charges and the number and type of side chains of

fiber molecuies, and the presence or absence of other nutrient molecules or substances in

the surroundhg environment. hcreasing the number of fiber molecular coils by inaeasing

dose is one way to increase the formation of raadom junction zones since the probability

of fiber chains coüiding with one another inmeases. Therefore, as psyllium dose increased,

viscosity and hardness Ievels were both proponiody higher.

Moreover, the application of heat treamiem to p s y h m samples significantly increased

the hardness (viscosity) level that might due to an addition of energy to hasten the process

of viscosiry and gel developmem and an increase in the availability and strength of fiber

coüs to interact and fom stronger imemio1eda.r bonding. The processes of heating

(thermal energy) and s thhg (mechanical energy) may help release more rnolecular coils

nom within the £%er sacs and accelerate the h r d e r e d phase of viscosiqr developmem

Furthemore, coohg may decrease rnolecuiar energy while inmeases the interaction of

molecular coils and the stabilay of the imermolecularjunction zones in the ordered phase

(Whistler, 1993). Therefore, with the addition of thermal and mechanical energy, the

resulting polysaccharide network formation becomes stronger and highly viscous.

The strength of the gel network depend on the strength of intemolecular bonding at

the junction zones. If the bonding is weak, it may be broken by even mild stimng and the

gel structure will be disrupted. In this case, the weak gel is referred to as thkotropic. In

the expenment detennining the optimal method to develop highly viscous fiber and

glucose mixtures, the treated samples which were stirred during cooling lost the high level

of viscosity and were not any different fiom the untreated samples. Sufficient energy was

supplied by the forces of stimng to break many of the junction zones and thus, the

resulting viscosity of the dispersion decreased. It is very possible that gels of the higher

psyllium dose (6g and 9g) may not be as easily broken by stiïring due to stronger junction

zones formation. However, this series of treatment experiments were done only with the

lowest psyllium dose (3g) and this hypothesis could not be tested. Finally, the process of

viscosity and gel development had been shown to be reversible by both heating and

cooling procedures. As the treated fiber and glucose mixtures were reheated, gels re-

liquefied as the junction zone energies were low enough that simple heating energized the

molecules sufficiently to cause them tear apart fiom each other. Cooling after re-heating,

conversely, decreased molecular energies and stabilized junction zones.

Viscosity levels of the heat-treated samples were unobtainable due to very high

viscosity levels. During heat processing, the rapid release of energetic psyliîum coils into

the surroundhg glucose and water mixture enhances the interaction and result with

junction molecuiar zones that are more difncult to break Energy coxning from the spindle

of the viscorneter is not d c i e n t to cause breakage between junction zones. Thus,

another rheological property of polysaccharides, hardness, which highiy correlated with

viscosity, could be used to indicate the relative viscosity levels of the heat-treated sarnples.

In conclusion, viscosity can be increased by increasing fiber dose, as well as by

applying heating, mWng and cooling treatments. Glucose solution is used in this

experiment because there is no evidence for glucose concentration influencing the heat

generated increase in fiber viscosity. Viscosity and hardness are highly correlated;

therefore, hardness measurements could be used to indicate the relative viscosity levels of

the heat-treated samples with which viscosity measurements were unobtainable.

Chapter 3

PHYSIOLOGICAL TESTING :

EFFECT OF VISCOSITY MODIFICATION BY

PSYLLIUM DOSE AND HEAT TREATMENT

ON POSTPRANDIAL BLOOD GLUCOSE RESPONSE

3. PHYSIOLOGICAL TESTING : EFFECT OF VISCOSITY MODIFICATION BY PSYLLLUM DOSE AND

EEAT TREATMENT ON POSTPRANDW BLOOD GLUCOSE RESPONSE

3.1 Introduction

The main objective of this study was to develop a mode1 to examine the effects of meals of a

wide viscosity range on postprandial blood glucose response. Such an in vitro mode1 was

developed and was described in chapter two. Fiber dose and heat treatment were two modalities

used to increase viscosity levels. The purpose of this chapter was to study the effect of rnodiS>ing

meal viscosity by psyllium dose and treatment method on postprandial blood glucose response. In

order to understand the effect of interaction between fiber coils and nutrient molecules on

viscosity and consequently on blood glucose changes, meals were tested at two nutnent levels

(25g and 50g CHO). The present chapter describes the 16 physiological tests done with hurnan

subjects.

Previously, dose of psyllium in the form of e ~ c h e d breakfast cereals has been found to be

inversely correlated with postprandial blood glucose response (Wolever et al., 199 1). However,

this relationship has not been studied with liquid rneals or highly viscous meals induced by heat

treatment. Thus, it is interesting to examine the dose effect of psyllium-containing glucose meals,

either untreated or heat-treated, on glucose response.

Results will be presented first to examine the dose effect of psyllium on postprandial blood

glucose response of the untreated, foiiowed by the heat-treated meals. Then, the effect of heat

treatment as a mode of increasing test meal viscosity on postprandial blood glucose change will be

evaluated. Finaiiy, results nom d meals at the NO nutrient levels will be compared and analyzed

to investigate the interaction between fiber coils and nutrient molecules.

3.2 Materials and Methods

3.2.1 Subiect recruitment and profile

Healthy students and staff, with no previous history of diabetes or related metabolic disorders

from the Department of Nutritional Sciences, University of Toronto, were recruited to participate

in the study. Written consent (Appendix 1), approved by the Ethic Cornmittee of St. Michael's

Hospital, was obtained from each subject after they were fully informed about the procedure and

involvement required in the study.

Eight (4 male + 4 female) normal subjects were recruited with mean age of 33.6k3.5 years,

body mass index (BMI) of 24.6h1.1 kgh? and fasting blood glucose level of 4.3I0.1 rnmoVL.

Subject characteristics were listed in table 3-1.

Table 3-1. Subject Profile

Characteristics Total (II=$) Males (n=4) Females (n=4)

BMI (kg/m2) 24-6 k 1.1 26.1 + 1.3 23 .O f 1.3

Fasting blood 4.3 f O. 1 4.3 k0.1 4.3 + 0.1 glucose

(mmoUL) (3.8 to 4.7) (3.9 to 4.6) (3-8 to 4.7)

3.2.2 Exaerimen ta1 desien

This study employed a single-blinded, randomized design with each subject serving as his or

her own control. Experimental meals, either heat-treated or untreated, included two nutrient

levels of control (25g and 50g CHO), given alone or each supplemented with either three, six, or

nine gram of psyllium. Al1 subjects were tested on 20 occasions. A tbtal of 16 different

experimental meals, including 12 psyllium-containing meals and four controls were administered.

Each of the four controls was repeated to standardize intra-individual variation. Meals were given

in a randomized order. Sequence of test order was as follows :

Subjects were asked to repeat a specific test if the result was signincantly different (f2 SD) from

the group mean.

3.2.3 Meal ~renaration

Composition of the 16 experimental meals was described in table 2-1. Al1 meals were

prepared in the metabolic kitchen at the Risk Factor Modification Center of St. Michael's

Hospital 24 hours before each test. Controls were given either as a combination of 100 mL

glucose solution (Glucodex, Rougier inc., 25g carbohydrate) and 200 mL distilled water or 200

mL glucose solution (50g carbohydrate) and 100 mL distilled water. Total meal volume was

standardized to 300 mL. Fiber test meals, in addition, contained either three, six, or nine grarns of

psyllium.

For the untreated meals, fiber was added to the glucose solution with vigorous mixing at room

temperature (23OC) for ten minutes. Then, the fiber meais were left at room temperature for three

hours with stimng every 15 minutes to allow for viscosity development and mixture homogeneity.

MeaIs were stored in the refngerator (4OC) ovemight.

For the heat-treated control and fiber test meals, pre-measured glucose solution and water was

fira heated to 100°C. Control meals were boiled for an additional ten minutes before removing

from the stove. For the fiber test rneals, psyllium was added to the boiling solution with vigorous

mixing and intermittent lifting for interaction with cool air for ten minutes. AI1 meals were left to

cool d o m to room temperature for three hours without further mixing and were stored in the

refnperator ovemiçht at around 4°C. Pnor to consumption, 24 hours after initial mixing, meals

were warmed up in room temperature for 15 minutes.

3.2.4 Studv Procedure and Blood Sample Collection

Subjects were asked to come to the Risk Factor Modification Center at St. Michael's Hospital

at 9:00 am after a 12 hour ovemight fast. Finger-prick capillary blood samples (3-4 drops) were

obtained at fasting, and at 15, 30, 45, 60, 90 and 120 minutes after consumption of the control or

test meals for blood glucose concentration measurements. Before collecting the fasting blood

sample, subjects were asked to be seated for ten minutes. M e r the fasting sample, subjects were

instructed to consume the given rneal steadily in ten minutes and were asked to remain seated

throughout the test. Finger-pnck capillary bliod samples were obtained with Autolet Lancets

(Owen Mudord Ltd., Woodstock, Oxon). Blood samples were collected into pre-labeled fluoro-

oxalate tubes and were kept frozen at -20°C prior to glucose analysis within 48 hours. Subjects

were also requested to fil1 out a questionnaire consisted of specific questions on prior meals and

activities, satiety levels at 0, 30, 60, 90 and 120 minutes during the test, paiatability levels of meal,

and side effects experienced (within 24 hours) afler the test (Appendk II).

3.2.5 Blood elucose analvsis

Capillary blood glucose concentration was rneasured using an automatic analyzer (2300 Stat

Glucose Anaiyzer, Yellow Springs Instnhents, Yellow Springs, OH) which utilizes the glucose

oxidase method (Shimizu et al., 1980). A standard glucose solution of 10.0 rnmoVL, prepared by

rnixing 1.8 grarns glucose powder with 1.0 L of distilled water, was used to calibrate the

equipment before measurernent. Blood samples were anaiyzed only after two successive readings

of the standard solution between the range of 9.9 to 10.1 rnrnoVL were obtained.

3.2.6 Statistical analvsis

Results were expressed as meankstandard error (SE). Incremental areas under the ducose

curves (AUC), ignonng area beneath the fasting level, were calculated geometncaiiy (Wolever et

al., 1991). Statistical cornparison of data at specific times, glucose peak, and AUC was by

ANOVA and student's t-test. The Newman-Keuls method was used to adjua the individual

means for multiple comparisons. Pearson test of correlation was done to determine the degree of

correlation between two variables. All anaiyzes were performed with the use of a statistical

software: Primer of Biostatistics (version 3, McGraw HU, 1992). DiEerences were considered

statisticdy significant if p<0.05.

3.3 Results

3.3.1 Psvllium dose effect (untreated mealsl

Overall blood glucose nse (Figure 3-la and b) and incremental area under the curve (AUC)

(Figure 3-2a) at both 25g and 50g carbohydrate levels decreased with increased psyllium dose.

Table 3-2 (25g CHO) and table 3-3 (50g CHO) showed the mean blood glucose concentrations at

specific times, the AUC and the glucose peaks of control and fiber tests. The following sections

described the specific findings at each nutrient level.

3.3.1.1 Low nutrient l eve l (25~ carbohvdratel

Fasting glucose values were not significantly different between tests (p=0.504). BIood

glucose concentrations at 15 minutes were significantly different between al1 control and fiber

tests (p<0.0001) and control was different significantly Frorn 6g and 9g tests (p<0.0001) at 30

minutes (the peak). 9ç test was significantly different fiom control and 3g and 6g tests at 120

minutes (p=0.028). Incremental areas under the curve were 120.5k12.4, lOO.7k 14.0. 87.3k4.9

and 82.6f8.4 mrnol.min/l for control, 3g, 60, and 9s respectively with 6s and 9ç tests

significantly different From control (pc0 -000 1).

Log hardness, which was directly proportionai to dose of psyllium (r=0.99, p=0.005), was

inversely correlated with AUC (r=-0.99, p=0.0062) (Figure 3-3a).

3.3.1.2 Hieh nutrient level(50g carbohvdratel

Results were similar to those obtained with 2Sg carbohydrate. From the blood glucose

response curve (Figure 3-lb), sigiificant difference in blood glucose concentrations between

control and 6g and 9g tests was seen at 30 (the peak) and 45 minutes (p<0.0001). Incrernentai

Blood glucose concentration (mmoVL)

P UI Q) m

Blood glucose concentration (mmoyL)

O P ul Q> m

Incremental blood glucose area (mmol.min/L)

-. O

lu O

O O O O

O O

Incranenta1 blood glucose area (mmol.minA,)

4

O ru O

W O O O

O O

Table 3-2. Blood glucose concentrations at specific time points, incremental areas under the curves (AUC) and glucose peaks of different untreated control and fiber test meals at 25s carbobydrate level (n=8).

Psyllium Blood glucose concent ration (mmoVL) AUC Peak

(g) (mmol.min/L) (mrnoVL)

O' 15' 30' 45' 60' 90' 120'

Values are meansfstandard error (SE). Means with different letter superscripts within a colunin differ significantly (p<0.05) as determined by ANOVA followed by Neunian-Keuls met hod..

Table 3-3. Blood glucose concentrations at specific time points, incremental areas under the curves (AUC) and glucose peaks oidiiierent untreated control and fiber test meals at 50s carbohydrate level (n=8).

Psyllium Blood glucose concentration (mmoVL) AUC Peak

(g) (mmoi.rnin/L) (mmoVL)

O' 1 5' 30' 45' 60' 90' 120'

Values are meansfstandard error (SE). Means with different letter superscripts within a column differ significantly (~€0.05) as determined by ANOVA followed by Neuman-Keuls niethod.

1 0 Log hardness

(a) Untreated meals

Figure 3-3.

1 0 100

Log hardness

(b) Heat-treated meais

Correlation between log hardness and AUC of (a) untreated and (b) heat-treated meals at 25g and 50g CHO levels (n=8)

areas under the curve were 208.3116.3, lgS.9f 12.9, 173.0k18.8 and 163.3k12.4 mmol.min/l for

control, 3g, 6 g and 9g tests respectively with signifiant differences observed between control

and 6g and 9g tests (p=O.O 19)- and between 3g and 9g tests (p=O.O 19).

Similar to the 25% CHO level, log hardness was also directly proportional to psyllium dose and

inversely correlated with AUC (F-0.96, p=0.0397) (Figure 3-3a).

3.3.2 Psvllium dose effect (heat-treated meals)

Overall blood glucose rise (Figure 3-4a and b) and incremental blood glucose area (AUC)

(Figure 3-2b. p.54) were slightly but proportionally correlated with psyllium dose at 2Sg and 50ç

CHO. Table 3-4 (25ç CHO) and table 3-5 (50g CHO) showed the mean blood glucose

concentrations at specific times, the AUC and the glucose peaks of control and fiber tests.

Detailed results are shown below.

3.3.2.1 Low nutrient level(25~ carbohvdrate)

Fasting glucose values were not significantly different between tests (p=0.467). Blood glucose

concentrations of control were signiticantly diferent fiom ail fiber tests at 15, 30 and 45 minutes

(pC0.000 1) with the 3g test also significantly dEerent fiom the 9g test (pc0.0001) at 45 minutes.

No other point of difference was observed between fiber teas. Incrementai areas under the curve

(AUC) were 1 15.6t13.7, 8 1.5t11.2, 59.516.7 and 39.8k3.2 mrnol.min/L. for controI, 3g, 6g, and

9g tests respectively. AUC of the control was significantly dîerent from the fiber tests

(p<0.000 1). while the 3g test was significantly different from the 9g test (p<0.000 1).

Log hardness, which was directly proportional to psyllium dose (r=0.97, p=0.043), was

inversely correlated with AUC (1-1 -00, p=O.OO 14) (Figure 3-3 b, p.57).

Blood glucose concentration (mmoik)

P UI 0) a0

Blood glucose concentration (mmoVL)

O P UI aD

Table 3-4. Blood glucose concentrations at specific time points, incremental areas under the curves (AUC) and glucose peaks of different heat-treated control and fiber tests meals at 25g carbohydrate level (n=8).

Psyllium Blood glucose concentration (mmoYL) AUC Peak

(g) (mmol.min/L) (mmoVL)

O' 1 5' 30' 45' 60' 90' 1 20'

Values are meansfstandard error (SE). Means with different letter superscripts within a column differ significantly (pK0.05) as detemined by ANOVA followed by Neuman-Keuls method..

Table 3-5. Blood glucose concentrations at specific time points, incremental areas under the curves (AUC) and glucose peaks of different heat-treated control and fiber test merls at 5Og carbohydrate level (n=8).

Psyllium Blood glucose concentration (mmoVL) AUC Peak

(s) (mmol.min/L) (mmoüi,) 0' 15' 30' 45' 60' 90' 120'

Values are meansistandard error (SE). Means with diflerent letter superscripts within a column differ significantly (p<O.OS) as detennined by ANOVA followed by Neuman-Keuls method.

3.3.2.2 Hirh nutrient level(50r carbohvdrate)

From figure 34b, significant difference in blood glucose concentrations between control and

al1 fiber tests was seen at 30 (p=0.007), 45 (p<0.0001) and 60 (p<O.0001) minutes while no

difference was observed between any of the fiber tests at any time point. lncremental areas under

the curve were 21 1.3kl8.4, l5O.Ok6.5, 137.2k13.3 and 133.4k12.9 mmol.min/L for control, 39,

6g, and 9g tests respectively. AUC of the control was significantly different fiom the fiber tests

(p<0.000 1 ) while no difference between fiber tests was observed.

Loç hardness was inversely correlated with AUC (-0.93, p=0.04) (Figure 3-3b) at the 50g

carbohydrate level.

3.3.3 Comparison between the untreated and heat-treated meals

3.3.3.1 Con trols

Control meals, either heat-treated or untreated, produced similar postprandial blood glucose

response at 253 (Figure 3-Sa) as well as 50g CHO levels ('Fiçure 3-Sb). No significant difference

at any time point, the AUC or the glucose peak was observed between controis prepared by

different methods,

3.3.3.2 Low nutrient level(25p carbohvdrate)

Heat treatment significantly increased hardness of fiber test meals and reduced postprandial

blood glucose response. The combined results fiom the untreated and heat-treated control and

fiber test meals showed that al1 heat-treated fiber meals (3, 6, and 9g), as a group, produced

glucose response considerably lower than the untreated meais (Figure 3-2). Incremental area

O 30 6 0 90 120

Time (minutes)

(a) 25g carbohydrate

O 30 6 0 90 120

Time (minutes)

(b) 5Og carbohydrate

Figure 3-5. Cornparison between controls, untreated or heat-treated, at (a) 258 CHO and @) 50g CHO (n=8)

under the curve of 3g heat-treated fiber meal was similar to the 9g untreated meal, with no

significant difference at any time point or in AUC observed.

Log hardness of test meals was inversely correlated with AUC (r-1.00, p=0.0001) when

considering both the untreated and heat-treated results (Figure 3-6).

3.3.3.3 H i ~ h nutrient l eve l (50~ carbohvdrate)

Sirnilar results were obtained afier combining the data for both untreated and heat-treated

meals. Treated fiber meals, as a group, had lower postprandial blood ducose response than

untreated meals. Log hardness of test meals prepared by both treatment methods was inversely

correlated to AUC (r=-0.94, p=0.0004) (Figure 3-6).

3.3.3.4 Com~arison between low ( 2 5 ~ ) and high (SOe) carbohvdrate levels

Meals of two different nutnent levels with the same hardness did not produce the same blood

glucose response (Figure 3-6). Glucose response of the 50g CHO meals was approximately 45%

higher than the 25g CHO meais. Thus, nutnent level should be a factor taken into account when

cornparhg çlycemic response of meals based on viscosity level. M e r nutnent level has been

adjuaed by expressing AUC per gram of carbohydrate present in the meais, log hardness of al1

untreated and heat-treated meais significantly correlated with AUCIg CHO (r-0.94, pc0.0001)

(Figure 3-7) (Table 3-6).

On the other hand, fiber-to-nutnent ratio ploned agaha glycernic index

{(AUC~~/AUC~bl)X1OO}, was inversely correlated in both the untreated (r=-0.95, p=0.0043)

(Figure 3-8a) and the heat-treated meal groups (-0.98, p=0.0009) (Figure 3-8b) (Table 3-6).

10

Log hardness

259 - untreated 259 - treated

M 509 - untreated A 509 - treated

Figure 3-6. Correlation between log hardness and AUC of aii heat-treated and untreated me& at 25g and 50g CHO levels (na)

259 - untreated 259 - treated

w 50g - untreated A 509-treated

Figure 3-7. Correlation between log hardness and AUC per gram CHO

of ai i me& (n=8)

o. 1 0.2 O .3

Fiber-to-nutrient ratio (g psyJg CHO)

(a) Untreated meals

0.1 0 -2 0.3

Fiber to nutrient ratio (g. psy/g CHO)

I a 259 untreated 50g untreated l

25g treated

(b) Heat- treated meals

Figure 3-8. Correlation between fiber-to-nutrient ratio and glycemic index of (a) untreated and (b) heat-treated meals (n=8)

68

3.4 Discussion

The purpose of this study was to examine the effect of modiwng psyllium meal viscosity on

postprandial blood glucose response. Since the main goal was to develop a study mode1 which

covered a wide range of viscosity (hardness: 5g to 650g) with one single fiber type, two variables,

fiber dose and heat treatment were introduced. Increasing fiber dose fiom Og (control) to 9g

psyllium in untreated meals only covered the lower third of the logarithmic hardness scale. When

heat treatment was introduced, hardness of meals increased significantly, covering the upper

portion of the logarithmic scale.

In this expenment, three doses of psyllium (3, 6, or 9g) were supplemented to two levels of

glucose control meals (2Sg and 50s CHO) to determine the dose and also the fiber and nutrient

interaction effects. As hypothesized, dose of psyllium, which was positively and linearly

correlated with viscosity and hardness of meais at both 25g and 50g CHO levels, was inversely

correlated with postprandial blood glucose response. In other words, the higher the psyllium

concentration in meals, the lower the AUC and the glucose peak. Results were consistent with

previous findings which showed a significant dose effect of psylliurn-e~ched cereais on

postprandial blood glucose and insulin responses (Wolever et al., 199 1).

Increasing the dose of fiber increases the number of fiber coils that may be available for

interaction with surrounding water and nutrient molecules. In addition, probability of fiber coils

randomly coiliding with each other increases, and the resulting network formation between coils

may become stronger due to an increase in junction zones and the progress from disordered

chains to ordered network. Nutnent molecules, glucose in this case, being entrapped within a

stronger network may have more difficulty escaping, or being released readiiy nom the gel matrix.

Therefore, in a physiological sense, these glucose molecules which are being held by an increased

number of fimly-attached fiber coils, will be released for absorption more slowly. More energy

or effort is necessary to break the bonds between the junction zones for the release of nutrients in

the çastrointestinal tract. Therefore, as fiber dose increased in meals with fixed nutrient level, the

longer the time required to break open the gel matrix and the slower the absorption rate of

glucose, as observed from the physiological results.

Fiber dose effect on postprandial blood glucose response was demonstrated in both untreated

and heat-treated meals. However, differences at different blood drawing time, in AUC and

glucose peak of heat-treated meals were only observed between controls and fiber test meals, with

no significant difference seen between 3g, 6g, and 9g fiber test meals with exception at the 25g

carbohydrate level. One possible explanation for the weaker dose effect of heat-treated meals is

the reaching to the physiological plateau. The percent reduction in AUC of fiber test meals per

çram fiber decreased with increasing fiber dose (Table 3-6, Figure 3-9). In other words, prams of

fiber present in the meal and its physiological effect is not a one to one ratio relation; rather, the

effect brought about by the initial çrams of fiber added to glucose meal was stronger, with

decreasinç effectiveness as the quantity of fiber in meal increased. Eventually, the reduction in

glucose response reached a plateau when the glucose response curves of the 6g and 9ç fiber meals

flattened. With the addition of fiber dose higher than 9ç, it is reasonable to speculate that oniy a

slight reduction in AUC will be possible.

Comparinç the postprandial blood glucose response curves and incremental areas under the

curves (AUC) of the untreated and heat-treated meals revealed that heat treatment significantly

reduced glucose response. The heat-treated meal with only three gram of psyllium produced the

sarne level of physioloçical effect as the untreated meal with nine grarns. In addition, the percent

reduction in AUC was sigiincantly dEerent between the two treatment groups with a doubling

Psyllium dose

Figure 3-9. Correlation between psyllium dose and % reduction in AUC

per gram psyllium of ali heat-treated and untreated meals

259 untreated 5Og untreated

H 25g treated

effect seen with the heat-treated meals (Table 3-6). The observed result was rather encouraging

to nutritionists and food producers because this proved that soluble fiber, afler special processing,

can be increased in efficacy by several fold. Thus, a lower quantity of fiber can be used to achieve

similar or even better physiological effects.

To determine whether heat treatment of glucose solution alone wilI have any effect on

postprandial blood glucose response, controls, either with or without treatrnent, were tested.

Results were not significantly different between the two controls, suçgesting that glucose-

lowering effect of heat-treated fiber meals was not due to losses or other changes in glucose

molecuies; but rather, due to the stronger entrapment of glucose molecuies within fiber matrix.

Despite improvernents in blood glucose response, side effects of heat-treated psyllium meals

(2+1 on a 10 point rating scale) experîenced by subjects were not different from untreated meals

( 1 . 5 ) Palatability of heat-treated meals was also reported to be more acceptable (8+1 on a 10

point rating scale) when compared to untreated meals (632). Thus, heat treatment seems to

provide several advantaçes over untreated meals.

From the nutntionist's point of view, it is obvious that by increasing the nutrient content in

meals, a higher blood glucose response will be resulted. However, fiom the rheological point of

view, if viscosity level is hypothesized to be the only parameter that will be important in

determininç blood çlucose response, it is interesting to note that meals (25ç and 50g CHO) with

identical hardness levels result in an approximately 45% difference in postprandial glucose

response. Therefore, nutnent level (grams carbohydrate) must be a variable that should be

factored in when studying the correlation between viscosity or hardness and glucose response.

M e r adjusting AUC for the difference in nutnent level @y dividing AUC by çrams of

carbohydrate present in the test meals), this ratio significantly correlated with log hardness. To

further prove that nutrient content in meals is

glucose response, the relationship between

another important and independent factor affecting

fiber-to-nutnent ratio and glucose response was

studied. The correlation between fiber-to-nutnent ratio and glycemic index of al1 25g and 508

CHO meals, either heat-treated or untreated, was found to be significant. This suggested that

other variables in the meal, fiber and nutrient concentrations in this case, may be useful in

explaining the discrepancy observed between rheological and physiological results.

By explaininç the results Rom the fiber coi1 and nutrient interaction point of view, it is easier

to understand what has happened physiologically. Supplying, for exarnple, 3ç psyliium to meals

of two different nutnent levels did not change the number of fiber coils available. As a result,

hardness measurements in both 25g and SOg CHO meals were almost identical, indicatinç similar

strength of junction zones which depended on the quantity of fiber coils presented. During

digestion, the rates of nutrient release and absorption might not be very different between the two

nutrient-levels meals tested under similar conditions as sirniiar efforts were required to break the

existinç bonds. However, the quantity of carbohydrate and the number of glucose molecules

presented were doubled in the 50g CHO meals. Therefore, for every release of a molecule from

the fiber coil matrix during digestion, the probability that it was a glucose rather than a water

molecule was much higher since twice the amount of glucose was present in the SOg CHO meals.

Furthermore. it could be speculated that each fiber coil atîracted a certain nurnber of nutrients,

with the ratio being unchanged at any fiber to nutnent concentrations. Thus, meals with the same

fiber-to-nutnent ratio, for example, 3g fiber and 25g CHO and 6g fiber and 50g CHO, produced

similar glucose response. Results frorn this experirnent suggested that predicting glycernic

response from viscosity or hardness measurement alone without considering nutnent level of the

test meds would give false results since viscosity and hardness of a test meal only indicate the

relative strength of the fiber coi1 junction zones, but not the type or number of molecules being

held or entrapped by the coi1 rnatnx. It was proven in this experiment that studying the

interaction of fiber and nutrient molecules was important to understand the physiological effects

of viscous fibers.

If dose of psyllium was plotted against glycemic index to study the effect of fiber dose on

ducose level, simiiar degree of change was observed between the 25g and 5Og CHO untreated

meals (Figure 3- 10). However, when interpreting the data from the heat-treated meals, glycernic

index of the 25ç CHO meals was linearly and inversely correlated with fiber dose; while a

flattened curve was observed with SOg CHO me&. This may suggest that heat treatment,

together with an increase in fiber dose, produce a more significant physiological effect only a low

nutnent level (25s CHO). No significant advantage was observed fiom heat treating hiçher

nutnent levef meais (50g CHO) with higher fiber dose (9g) when compared to lower fiber dose

(3g and 6ç). In addition, this may suggest that fiber given on a nutnent basis, rather than given as

a fixed dose, is a more appropriate approach when studying liquid meals.

In conclusion, this study showed that psyllium dose was inversely correlated with glucose

response at both 25ç and 50s carbohydtate levels, seen in both untreated and heat-treated meals.

Furthemore, increasinç viscosity by heat treatment provided a means to achieve physiological

effect that would not have been possible by rnodeng fiber dose alone. This innovative heat

treatment method was proved to be simple, convenient, inexpensive and also effective. However,

viscosity or hardness did not correctly predict glucose response of test meals at different nutrient

levels unless the ducose response was adjuned to a per gram nutrient basis. By combining results

of al1 heat-treated and untreated meals at 25g and 50g CHO levels, the viscosity modification

mode1 as a whole, demonstrated a significant inverse correlation between log hardness and

6

Psyliium dose (g)

EJ 25g untreated 25g treated

M 509 untreated

Figure 3-10. Correlation between psyilium dose and gIycemic index of

al1 heat-treated and untreated meals (n=8)

postprandial blood glucose response after accounting for the nutrient level in meals. Therefore,

viscosity of meals, even when preparation method is not known, is useful in predicting blood

glucose response as long as the nutrient content is taken into consideration.

Chapter 4

GENERAL DISCUSSION

AND

CONCLUSION

4. GENFRAL DISCUSSION AND CONCLUSION

4.1 General discussion

The major contribution of this study is the development of an unique approach to study

the effect of fiber viscosity on physiology. Furthemore, this study contnbutes to the

understanding of the mechanism of viscosity development with respect to the interaction

of soluble fiber and nutnents in attenuating the rate of glucose absorption.

Supplementing carbohydrate loads with soluble fiben such as çuar gum or pectin has

been show to reduce postprandial blood glucose and insulin concentrations (Jenkins et

al., 1978). However, results from different midies investiçating even the same fiber

source, but without refemng to its rheological properties, were not conclusive (Blackburn

et al., 1984; Uusitupa et al., 1989). In fact, rheoloçical properties of soluble fibers, such

as viscosity, rather than gravimetnc measurements done, have been suggested as

important factors when predicting physiological response (Moms et ai., 1990). Although

the relationship between viscosity and postprandial blood glucose lowering effect has been

well documented, many questions still remain. For example, simple measurement of fiber

viscosity in vitro does not always predict in vivo response (Edwards 1987). However, it

has been demonstrated that in vivo viscosity of digesta measured in an animai model is

better correlated to glycernic response (Eh et al., 1995). Therefore, a single numencal

measurement of in vitro viscosity may not necessarily be sutficient to predict physiological

effect and fully explain viscous fiber behavior. On the other hand, studying a particular

viscous fiber within a wide range of viscosity and taking into consideration the interaction

between fiber and nutrients seem to be a more plausible mode1.

In order to investigate the effect of viscosity, previous investigators (Jenkins et al.,

1978; Wood et al., 1994) have used acid hydrolysis in an attempt to rnodify fiber viscosity.

Dunng the process of acid hydrolysis, fiber polysaccharide chahs are broken down into

shorter segments that lead to structural changes and partial or even complete destruction

of viscosity. This means that the resulting materials are no longer soluble fiber by

definition. In contrast, a novel and practical method to maxirnize viscosity of psyllium was

introduced in this study. The heat treatment method proved to be simpler, less destructive

to fiber structure and more importantly, did not require the use of chernicals in modifjhg

viscosity. The purpose of heat treatrnent is to maximize the release of fiber coils to the

surroundinçs, while at the same time increasing their level of interaction. It also physically

leads to the formation of a stronger and highly organized polysaccharide structure which

increases entrapment of nutrients. The effect of heat treatment of meals with different

psyllium concentrations and nutrient levels was tested in human subjects.

There were several reasons for choosing psyllium as the test fiber. First, psyllium has

been shown to be metabolically active. tt is widely used in laxatives to prevent or treat

chronic bowel disorders (Fagerberg, 1982). Furthemore, psyllium has been shown to

lower blood cholesterol, glucose and insulin levels in humans (laris et al., 1984). Among

different soluble fibers, psylliurn is considered to be inexpensive, relatively palatable due to

its neutral taste and has a long history of safe use. However, viscosity level of psyliium is

considered at the lower rank when compared to some other soluble fibers such as

konjacmannan, guar, or xanthan. Since a large margin of increase in viscosity is possible,

psyllium is a good viscous fiber source to be studied. Three grains of psyllium was chosen

as the lowest fiber dose given with 25s and 50g CHO liquid glucose meals whicii

produced marginal physiological effect. Doubling and tripling this dose in untreated as

well as heat-treated meals were expected to produce dose and treatment related responses

in postprandial blood glucose, with the physiological threshold (plateau) reached only with

highly viscous meals. Therefore, this experimental design allowed for the study of

psyllium-supplemented meals covering a wide range of viscosity levels and physiological

effects.

Results of this experiment confirmed the hypothesis that in vitro fiber viscosity was

highly and inversely correlated to in vivo physiological response when nutrient content

was also taken into account. This phenornenon, interpreted from the level of interaction

between fiber coils and nutrients, contributed to the understandinç of the possible

mechanism of action. Durinç the process of viscosity development, fiber coils are released

and their ability to associate and form ordered networks £tom disordered molecular chains

increases (Moms, 1995). The degree of occurrence of this process determines the

resulting fiber viscosity level and its ability to entrap surrounding water and nutrient

molecules. Increasing the number of fiber particles by dose, while increasing the

availability and strength of fiber coils by heat treatment, considerably increased viscosity.

More precisely, by a combination of heating, mixhg and coolinç treatments, the process

of viscosity development might have been accelerated and maximized. As a result of the

stronger molecular network entrapping nutrients, the rate of glucose absorption in the

gastrointestinal tract was slower. With dose and heat treatment, glycemic index improved

from 83.5 to 34.4 at the 25g CHO level, and from 94.1 to 63.1 at the 50g CHO level

(Table 3-6). However, it is difficult to distinguish precisely whether the significant

postprandiai glucose reduction effect results fiom an increase in fiber coils available, from

a stronger matrix formation, or from both. From the results, it cm oniy be speculated that

both an increase in number and a stronger network formation have occurred. On the other

band, this audy shows that viscosity of liquid meals, without adjustment of nutrient

contents, does not predict physiological resuits. Viscosity of meals, including those with

different levels of fiber and nutnent concentrations, is an important parameter in predicting

postprandial blood glucose response only when those variables are also taken into

consideration.

4.2 Implications and Benefits

This audy demonstrated several potential implications, includinç economical, scientific

and health-wise benefits. To achieve considerable metabolic effects, relatively large

quantities of psyllium are usually required. Althouçh psyllium is çenerally well tolerated,

larçer quantities may become unacceptable by many individuals due to an increase in side

effects. In our experiment, the viscosity level of psyllium in glucose meals had been

successfùlly increased from 2.7 (3g) to over 16-fold (9g), after a combination of heating,

mixinç and cooling treatments. Physiologically, the level of postprandiai blood glucose

lowering effect produced by 9g untreated psylliurn was attained by using only 3 grams

heat-treated psyllium. As a result, with heat treatment, a lower quantity of psyllium (only

one-third of the original) would be needed to achieve at least equal or even stronger

physiological effect. Econornically, this leads to savings in terms of materials and money

afler considering for the cost of treatment, especially in long term use.

Using considerably less psyllium but achieving the sarne physiological effect is a geat

achievement and may potentially induce less gastrointestinal discornfort. In some long-

term studies, when higher doses of soluble fibers were given, unpleasant and intolerable

side eKects were experienced due to increased colonic fermentation. In this study,

treatrnent of psyllium by heat did not result in increased side effects (gas or abdominal

discornfort) despite an improved blood glucose Iowering response. One might expect that

lowered blood glucose response with increased dose and heat treatment resulted From

significant malabsorption of carbohydrate with a larger quantity of fiber entering the colon.

However, since subjects did not report significant increases in side effects with meals of

hiçher viscosity, it was suggested that psyllium did not cause a reduction in blood glucose

due to carbohydrate malabsorption, but rather due to a slower rate of absorption in the

small intestine. This speculation could be confirmed by the measurement of breath gases

in nonai patients and/or measurements of ileal effluent in ileostomic patients.

Furthemore, heat treatment improved the overall texture and palatability of the rneal.

Simple mixing of viscous psyllium with glucose results in a gummy and sticky texture.

which is considered unpalatable by many individuals. Compliance to the consumption of

large quantities of ymmy meals in long-term use would be doubtfil. One solution is to

incorporate soluble fiber into manufactured foods. Guar has been incorporated effectively

and palatably into cnspbreads (lenkins et al., 1978b). while psylliurn could be incorporated

into a ready-to-eat brealfaa cereal without loss of physiologie effect and with potential

gains in palatability (Wolever et al., 1991). This midy confirmed that by simple heat

treatment, the texture of psyllium-supplemented glucose rneals could be changed Eorn

ymmy and sticky to fûm, bit-fiesh and jelly-like. Palatability of the heat-treated meals,

with a 8 t l palatability rathg score, was considered more acceptable (p<0.05) than

untreated meals, with a 6k2 rating. Two subjects had even reported difficulty ingesting

the viscous 99 untreated meals. Therefore, besides econornical and physiological benefits,

palatability improvement was another advantage of heat treatment of soluble fibers.

Another concem with the use of psyllium is its potential allergenicity in hypersensitive

individuals. Psyllium seed hypersensitivity was reported in previous literature with

possible links to cases of asthma (Cartier et al., 1987; Scott et al., 1987) and allergic

rhinitis (Gauss et al., 1985; Schwartz et al., 1989). Exposure to psyllium seed husk

powder can cause IgE sensitization and IgE-rnediated allergic reactions in sensitized

individuals, while most allergic reactions occur following ingestion of psyllium products

(Seggev et al., 1984). The process of subjecting psyllium to heat treatment in the

production of psyllium-contained cereals has been s h o w to reduce allergenicity of

psyllium substantially (Kellogg, US Patent No. 527 1936). Compared to Kellogg's, the

heat treatment method adopted by the present study was simpler, with glucose solution

being the meal type investigated, and was conducted for a different purpose. Although

simpler, heat treatment of psyllium-contained çlucose meal might still provide an

advantage over untreated meals. However, the speculation that heat treatinç psyllium

with our simple method may decrease its dergenicity has to be investigated further.

As a larger proportion of the population is willing to consume and is able to afEord the

supplements of soluble fibers as part of their habitua1 diets, this rnay very well translate to

better prevention and treatment of chronic diseases such as coronary heat diseases and

diabetes in the tiiture. However, results obtained fiom this acute study should not be

extrapolated beyond their scope. In this study, promising results were s h o w with simple

glucose meals. In terms of solid and mixed meals that contain other nutrients such as

protein and fat, the strength of gel matrix formation might not necessarily be as strong and

stable as the fiber-glucose matrix because fiber coils might not be able to entrap larger

nutrient molecules as firmly and effectively. Moreover, when cornparhg the glucose

lowering effects of breakfast cereals either incorporated with heat-treated psyllium or

spnnkied with untreated psyllium, no significant differences were obsenred between the

two (Wolever et al., 199 1). Therefore, the difference in meal type as well as the

involvement of other procedures in the heat-processing rnethod may possibly be the

factors responsible for the decrease in efficacy of heat-treated psyllium-enriched cereals.

Future studies to explore and extend the use of highly viscous, heat-treated fiber products

will be essential to irnprove the efficacy and status of soluble fiber in preventing and

treating chronic diseases.

4.3 Conclusion

The main objective of this study was to examine the effect of rnodifjing meal viscosity

by psyllium dose and heat treatment on postprandial blood glucose response. In order to

understand the mechanism of how fiber and nutrient interacts and possibly affects viscosity

development, meals were tested at two nutnent levels.

In summary, a novel study method covering a wide range of viscosity and the

respective physioloçical response was successfilly developed by modifjhg dose of

psyllium and applying heat treatment. Renilts from the study showed that enhanced meal

viscosity by increasinç psyllium dose and heat treatment proponionally decreased

postprandial blood glucose response. If the effects of psyllium dose and heat treatment on

glucose response were exarnined separately, dose of psyllium, which was positively and

linearly correlated with viscosity and hardness of meals at both 25g and 5Og CHO levels,

was inversely correlated with postprandiai blood glucose response. Furthemore, heat

treatment increased viscosity of psyllium significantly, with less matenal required to induce

a similar level of physiological response. Heat treatment also improves palatability and

potentially decreases allergenicity of psyllium-contained meals, and is a usefùl mode1 in

studying the rheological-physiologicd relationship of soluble fiber.

In conclusion, meal viscosity is an important pararneter in predicting postprandiai blood

glucose response when nutrient content is also taken into consideration.

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30 Bond Street Toronto, Ontario M58 1W8

Risk Factor Modififaon Center

CONSENT FORM

A teaching hospilal aMliated with Ihe Universily of Toronto

Effects of different carbohydrate meals on postprandial blood glucose response

1, agree to participate in a study investigating the effects of different carbohydrate meais on postprandial blood glucose response. This study is being conducted by the Risk Modification Center at St. Michael's Hospital and the Department of Nutritional Sciences of University of Toronto.

I understand that I shall be asked to corne fasting (12 hours) to the clinic at 9:00 am in the morning to take a test mal. 1 aiso understand that I will give finger-prick capillary blood samples (3-4 drops) at O (fasting) and at 15, 30, 45, 60, 90 and 120 minutes after the start of the test meal. Finger pnck samples will be obtained using an automatic device designed for this purpose. 1 have been asked to remain seated and not smoke, eat or d h k over this period.

There is vimially no risk involved in this study other than possibly a slight discornfort experienced by the fingertip when blood is drawn.

The results from this study will be confidentid, unless 1 wish rny results to be provided to a third Party. 1 have read this consent form, have had al1 my questions about this study answered, and agree to be part of this study. If 1 have further questions, I may contact Dr. Vladimir Vuksan or Evelyn Wong at (416) 867-7475. I understand that 1 rnay withdraw Rom this study at any time with notification to the investigator. I have received a copy of this consent forrn.

Name of participant :

Signature of participant :

Signature of investigator :

Date :

Toronto's Urban Angel

Appendix II STUDY QUESTIONNAIRE

NAME : TEST: DATE :

night that was not part of your regula. routine? 1

1. Please describe the meaï you ate last night. (Inciude time of meal, the food eaten and serving sizes)

2. Did you have any aftcr-dinner snack last night? Uyes, please describe the snack

, and the time consumed. 3. Did you do anything unusual/ special last

If yes, please describe. 1

0 Yes n No

0 Yes O No

-

4. How many hours of sleep did you have last 1 hours night?

5. How wodd you describe your health statu at this moment?

6. Please describe any uncornfortable feeling you had last night or this morning.

1

8. What was your mode of transportation this 1

Excellent health O Fair

Poor

7. Did you do anything unusual or special this morning before thc test? If yes, please describe.

B. During Testing - Satiety and palatability rating

O Yes O No

Please indicate with an 'X' your satiety leveI for each of the designated testing times. O tirne (before consuming test food) (ion) 0 - - - - 5 - - - -- 10 @eh>

!

30 min. oow) o - - - - s - - - - 10 Oirnh)

60 min. oon) 0- - - - 5 - - - - 10 (Mm 90 min. ci- 0 - - - - 5 - - - - 10 Oilgh)

120 min. ~ O W ‘ I O - - - - S - - - - 10nilrhl

1 Palatability of the test meal oonl 0 - - - - 5 - - - - 10 (hlgh) 1

peak hour(s) after the test that you had this experience and also, mark an X at the

C. Post Testing - Side Effect Esperiences

peak hour(s) of side &cts

1. Did you experience flatulence or related discomfort within 24 hours f i e r consumption of the test meal? Ifyes, please indicate the

U Yes Ci No

Remarks :

appropriate place on the scale representing the severity level of your experience. flm) 0 - - - - 5 - n - - 10 @gh)

APPLIED IWGE , lnc = 1653 East Main Smet - -. , Rochester, NY 14609 USA =-= Phone: 71 W48&tXOû -- -- - - FE 7161288-5989