use of advanced drying technologies to produce … of advanced drying technologies to produce novel...
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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
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
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
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
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
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
Boualaphanh et al., Proc. 9th TSAE Conf., CR2-16 (2008)
Puffing
Boualaphanh et al., Proc. 9th TSAE Conf., CR2-16 (2008)
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.)
Opportunities & Challenges
• 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)
Opportunities & Challenges
• 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
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
(b) 2 months
b,ca,b
dd
ff
ee
cc
a a
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
(c) 3 months
c
e
f
b
cd
a ab b b b
Opportunities & Challenges
• 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)
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