use of advanced drying technologies to produce … of advanced drying technologies to produce novel...

Sakamon Devahastin

King Mongkut's University of Technology Thonburi (KMUTT)

Bangkok, Thailand

August 16, 2017

Use of Advanced Drying Technologies

to Produce Novel Snacks

Outline

• Needs for healthy snacks

• Alternatives for production of healthy snacks

• Selected results, opportunities and future

challenges

Snacks

• Dry crisp foods having structure consisting of

cells or cavities, filled with air, and structural

phase or cell walls formed by brittle matrix

CLSM images of potato cell walls (raw & fried)

Pedreschi and Aguilera, Food Sci. Tech. Int., 7: 1-5 (2002)

Snacks

• Snacks, e.g., potato chips, tortilla chips or other

fruit-based snacks are normally produced by

deep-fat frying in vegetable oils

• Frying produces products with desired texture

and organoleptic properties

• Unfortunately, fried snacks contain high

contents of oil – not desirable by health-

conscious consumers

Bouchon et al., J. Food Sci., 68: 2711-2716 (2003)

Moyano and Pedreschi, LWT, 39: 285-291 (2006)

Healthy snacks

• Drying (and baking) appears as alternative

means for production or low-fat (or even fat-

free) snacks

• Conventional hot air drying, however, leads to

products with poor texture and color

• Poor-quality dried snacks are due to less

porous structure, casehardening, browning

reactions, among others

Healthy snacks

• Advanced drying technologies with or without

appropriate sample pretreatments are possible

solution

• Drying technologies: hot air drying, vacuum

drying, MW-assisted drying, superheated steam

drying (SSD) and IR-assisted drying

• Pretreatments: freezing, puffing, foaming

Superheated Steam Drying (SSD)

• Proposed over 100 years ago; received serious

attention only during the past 20 years

• Uses steam in place of hot air or

combustion/flue gases in a direct dryer

• More complex than hot-air drying system

• Better product quality (in most cases)

Closed steam

drying system

Recycled steam

Fan/blower

Direct use of

steam

Energy recovery via

heat exchanger

Removal of

condensate

Heaterpurged steam

steam from boiler

Typical SSD set-up

Superheated Steam Drying (SSD)

Important phenomena during SSD

• Initial steam condensation, leading to:

• Slight increase in MC

• Rapid increase in surface temp.

• Absence of oxygen, resulting in:

• No oxidation reactions, e.g., enzymatic

browning, lipid oxidation, vitamin degradation

Initial condensation

Drying time

Mo

istu

re c

on

ten

tTem

pera

ture

Saturation temp. of steam

Superheated steam temp.

Rapid temp. rise

due to condensation –desirable in many cases!

Typical evolutions of material MC and temp. during SSD

Drying time

Mo

istu

re c

on

ten

tTem

pera

ture

In this period MC is still high while temp is also

quite high – this promotes:

• Rigorous internal moisture vaporization

• Starch gelatinization

Typical evolutions of material MC and temp. during SSD

Some advantages of SSD

• No oxidation reactions possible due to lack of

O2; color and some nutrients are better

preserved

• Casehardened skin is unlikely to form in SSD

• SSD yields higher product porosity due to

evolution of steam within the product

• Other heat treatments (e.g. blanching, boiling,

cooking) can be performed simultaneously

with drying

Set-up for production of fat-free potato chips

Iyota et al., Drying Technol., 19: 1411-1424 (2001)

initial condensation

Drying curves for both SSD and hot air drying

of potato slices

Iyota et al., Drying Technol., 19: 1411-1424 (2001)

SEM photos of cross section near the surface of potato slices

SSD

Hot air

Iyota et al., Drying Technol.,

19: 1411-1424 (2001)

SEM photos of cross section near the surface of potato slices

second-layer crust

Iyota et al., Drying Technol.,

19: 1411-1424 (2001)

SSD

Hot air

Low-Pressure Superheated Steam Drying

(LPSSD)

•Products that may melt, undergo glass

transition or be damaged at saturation

temperature of steam cannot be dried in SSD

•LPSSD has been proposed to alleviate such a

problem

•LPSSD products possess porous structure, good color & more nutrients

Hot air drying LPSSD

• Better color is due to absence of oxygen in LPSSD system – no

enzymatic browning

• Drying time in the case of LPSSD is shorter – less non-enzymatic browning

Enhancement of LPSSD can be done by…

• Use of IR (esp. FIR) as additional heat source

• More rigorous internal moisture vaporization

• Improved (?) surface color (in some cases)

Nimmol et al., J. Food Eng., 81: 624-633 (2007)

Commercial FD

product:

• Max. force ~ 56 N • No. of peaks ~ 17

Léonard et al., J. Food Eng., 85, 154-162 (2008)

LPSSD-FIR chips exhibited more color changes than LPSSD and VACUUM-

FIR chips

• Least color changes – go for LPSSD• Very crisp texture – go for LPSSD-FIR

•VACUUM-FIR can be a compromise between the two??

Enhancement of LPSSD can be done by…

• Use of appropriate sample pretreatments

• Blanching + freezing

• Blanching + Repeated freezing/thawing

• Enhanced starch retrogradation – better

mouthfeel and firmer texture can be achieved

Kingcam et al., J. Food Eng., 89: 72-79 (2008)

Opportunities & Challenges

• Appropriate pretreatments can be used to

improve texture of potato chips

• Full sensory test is suggested

• Commercially, time scales use for freezing/

thawing may not be practical

• How to effectively apply flavors??

Puffing

• Involves release or expansion of vapor or gas

within material to create internal structure or

to expand and/or rupture structure

• Can simply be achieved by high-temp. short

time (HTST) heat treatment

• Rapidly induced vaporization of vapor (or

expansion of gas) leads to porous structure –

texture is improved

HTST

Pre-drying step: Drying by hot air to reduce MC to lower value

Puffing step: Puffing at higher temp.

(e.g. SSD at 150 oC) for short period of time (say, 1-3 min)

Post-puffing step: Drying by hot air until final MC has been reached

Puffing

Structural changes of bananas at different times during HTST (150oC–15 min)/hot air

drying process (HAD)

(a) Fresh banana sample; (b) after 3 min of HTST pulse; (c) after 9 min of HTST pulse; (d) after 12

min of HTST pulse; (e) after 22 min of the cooling period; (f) after 37 min of the cooling period; (g)

after 5 h of the HAD

Hofsetz et al., J. Food Eng., 83: 531-540 (2007)

HAD at 90 oC

Puffing at 180 oC for 2 min

Boualaphanh et al., Proc. 9th TSAE Conf., CR2-16 (2008)

Banana microstructures

Puffing

Hofsetz et al., J. Food Eng., 83: 531-540 (2007)

Puffing temp., puffing time and intermediate MC (before puffing) affect

volume expansion of sample (which is related to shrinkage)

Intermediate

moisture content

(% d.b.)

Temperature

(oC)

Puffing time

(min)

Shrinkage

(%)

25

160

1 38.49

2 29.24

3 25.25

170

1 21.62

2 4.50

3 3.48

180

1 26.60

2 10.87

3 12.47

30

160

1 42.36

2 40.33

3 34.11

170

1 33.27

2 34.44

3 31.84

180

1 29.39

2 18.14

3 17.17

Puffing at 170 C for 2 min,

IMC of 25% d.b.

More porous structure after post-puffing drying

Puffing at 180 C for 2 min,

IMC of 25% d.b.

Puffing


Puffing


Temperature

(oC)

Puffing time

(min)

Hardness

(N)

Number

of Peaks

Initial Slope

(N/mm)

160

1 40.18 24 27.92

2 50.91 24 22.30

3 56.74 20 27.93

170

1 25.74 33 22.74

2 23.07 34 32.60

3 25.10 26 31.43

180

1 39.23 34 33.68

2 33.00 37 35.31

3 37.57 28 27.54

IMC = 25 % (d.b.)


• Puffing can help improve product texture

• Color of product may not be totally satisfied

due to the use of high-temp puffing medium

• Other HTST processes (e.g., MW) may be

attempted

Foaming

• A process by which liquid or semi solid foods

are whipped to form foams

• Two types of foaming agent are used in foods:

• Low-molecular weight emulsifiers (lipids,

phospholipids, surfactants)

• High-molecular weight biopolymers (proteins and

polysaccharides)

• Proteins are widely used as ingredient for

foam formation and stabilization

Foaming

• Outcome of protein adsorption is reduction in surface tension,

which improves foam formation

• Viscoelastic films are generally resistant to rupture and to coalescence of gas bubbles dispersed in the liquid phase

Foaming

Base material is blended to puree

Foam is dried to desired moisture content

Puree is added with foaming

agent and whipped

Foaming

If foam is unstable, collapse of porous structure occurs, resulting in poor foamed product quality!

Light microscopic images of banana foams (using WPC as foaming agent)

Foaming

Morphology of dried banana foams

0.3 g/cm3 (EA) 0.5 g/cm3 (EA)


• Foaming can help improve product texture

• Porous structure of dried foams presents

storage stability problem - open structure may

be sensitive to moisture adsorption (leading to

poorer texture) and oxidative deterioration

Effects of storage time and temperature on

crispness of dried banana foams

0

5

10

15

20

25

30

Fresh product Stored at

7ºC

Stored at

29ºC

Stored at

40ºC

Num

ber

of peaks

0.21 g/cm³

0.26 g/cm³

0.30 g/cm³

(a) 1 month

b

d

e

a,b

d

e

a

c

e e

c

a,b

0

5

10

15

20

25

30


7ºC

Stored at

29ºC

Stored at

40ºC

Num

ber

of peaks

0.21 g/cm³

0.26 g/cm³

0.30 g/cm³

(b) 2 months

b,ca,b

dd

ff

ee

cc

a a

0

5

10

15

20

25

30


7ºC

Stored at

29ºC

Stored at

40ºC

Num

ber

of peaks

0.21 g/cm³

0.26 g/cm³

0.30 g/cm³

(c) 3 months

c

e

f

b

cd

a ab b b b


• Dual-density foams are among possible

solutions

• Low-density foam (porous) may be sandwiched

by high-density (dense) foams

Conclusion

• Advanced drying technologies have potential

for production of healthy snacks

• More studies are still needed!

This is not the end. It is not even the beginning of the end. But it is the end of the

beginning (or not??)

Modified from the famous quote of Sir Winston Churchill

Acknowledgements

• National Science and Technology Development Agency (NSTDA)

• Thailand Research Fund (TRF)

• Commission on Higher Education (CHE)

use of advanced drying technologies to produce … of advanced drying technologies to produce novel...

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