16/04/2013 1 Creating microstructure of dehydrated fruits and vegetables with a multi-flash drying process João B. Laurindo Barbara Porciuncula (PhD student) Marta F. Zotarelli (PhD student) Ricardo Monteiro (MS student) ESPCA/São Paulo School of Advanced Science Advances in Molecular Structuring of Food Materials Creating microstructure of dehydrated fruits and vegetables with a multi-flash drying process Federal University of Santa Catarina, Florianópolis-SC, Brazil Department of Chemical and Food Engineering Campus Universitário – Trindade – 88040-900 [email protected]João B. Laurindo Barbara Porciuncula (PhD student) Marta F. Zotarelli (PhD student) Ricardo Monteiro (MS student)
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16/04/2013
1
Creating microstructure of dehydrated fruits and vegetables with a multi-flash drying process
João B. LaurindoBarbara Porciuncula (PhD student) Marta F. Zotarelli (PhD student) Ricardo Monteiro (MS student)
ESPCA/São Paulo School of Advanced ScienceAdvances in Molecular Structuring of Food Materials
Creating microstructure of dehydrated fruits and vegetables with a multi-flash drying process
Federal University of Santa Catarina, Florianópolis-SC, BrazilDepartment of Chemical and Food EngineeringCampus Universitário – Trindade – 88040-900 [email protected]
João B. LaurindoBarbara Porciuncula (PhD student) Marta F. Zotarelli (PhD student) Ricardo Monteiro (MS student)
Convective-multi-flash drying process – CMFD (banana)
Evolution of the pressure in the jacketed container and fruit temperature during the CMFD process applied to banana samples
Evolution of experimental moisture content of banana during the CMFD process and the estimated contribution of flash-evaporation to the whole drying process
Evolution of banana samples water activity during the processing.
Water activity
Drying curve
Flash-drying contribution
Convective-multi-flash drying process - CMFD
After flash evaporation (= flash cooling) heat transfer from hot air (70 0C) to the
fruits is improved by the high temperature difference between hot air and cooled fruits
During flash-evaporation part of the internal moisture is drained to the fruit surface
and improve evaporation during the heating step (convective drying)
Pictures of mango fruits after every heating-vacuum pulse cycle
Pictures of mango fruits after 12
cycles of heating-vacuum pulses
CMFD cycles
Some pictures of mango during dehydration by CMFD
SEM of freeze-dried mango - 20x
SEM of mango dehydrated by CMFD – 20x
SEM of oven-dried mango – 20x
DEHYDRATED MANGO
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Puncture tests of dehydrated mango
0
5
10
15
20
25
30
35
0 10 20 30 40 50 60 70
Fo
rce (
N)
Strain (%)
Dried by hot air
Dried by CMFD
Freeze-dried
Jagged curves crispy foodsNumber of peaks, fractal dimension
SEM of freeze-dried banana- 20x
SEM of banana dehydrated by CMFD – 20x
SEM of oven-dried banana – 20x
DEHYDRATED BANANA
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10
0
2
4
6
8
10
12
14
0 10 20 30 40 50
Deformação Relativa (%)
Fo
rça
(N
)
Banana "in natura" seca por 12 CAPV
Banana Liofilizada Comercial
Dried by CMFD
Freeze-dried Strain (%)
Forc
e (
N)
Puncture tests of dehydrated banana
Jagged curves crispy foodsNumber of peaks, fractal dimension
REMARKS
It is possible to produce dried-and-crisp fruits using the
convective-multi-flash drying process (CMFD) with texture
properties that are similar to those obtained with freeze-drying
Product color is preserved due to the use of moderate process
temperatures ( Do you want it? )
Process time of CMFD and KMFD are shorter (about 2-3 hours
at laboratory scale) than the characteristic times of freeze-drying
Equipment and process are simple and use low pressures and
temperatures smaller investment and energy requirements
than freeze-drying
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Can we control the microstructure of dehydrated fruits and vegetables?
How can we follow the microstructure evolution during drying?
YES, WE CAN!
Bulk or apparent volume
Vb= apparent volume (cm³)mb= sample weight in air (g)ma= support mass (g)mb1= “sample weight” immersed n-heptane (g)ma1= support weight immersed in n-heptane (g)
1 1( ) ( )b a b a
b
solvent
m m m mV
d
Becker with n-heptane
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True volume of a porous material using a gas picnometer (Sereno et al., 2007)
Vp= true volume (cm³)Moist material = volume of the solids forming the sample structure + volume of the liquid Dry material = volume of the solids forming the fruit structure
V1 V2
Material porosity,
Vb= bulk volume (cm³)Vp= true volume (cm³)
1001%
b
p
V
V
10010
b
bb
V
VS
Accessible porosity during drying
Accessible porosity increases at each cycle of CMFD or KMFD during drying
Fruits shrinking during drying
Vb0
Vb
FROM THE BULK VOLUME AND THE TRUE VOLUME
WE CAN DETERMINE
shrinking patterns
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SEM- Scanning electronic microscopy
Samples preparation fruit slices were removed from thedryer, frozen by liquid nitrogen and freeze-dried(It was considered that ultra rapid freezing and freeze-dryingdid not change significantly the fruit structure)
Convective drying
T = 60 °C
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0
1
2
3
4
5
0 250 500 750 1000 1250 1500
Tru
evo
lum
e (
cm³)
Time (min)
Strong shrinking
True volumeof dried fruits
True volumes (solid + liquid)as determined with the gas porosimeter
1001%
b
p
V
V
0
10
20
30
40
50
60
70
0 250 500 750 1000 1250 1500
Vo
idsp
ace
s(%
)
Time (min)
Porosity of dried fruits(57%)
Evolution of the void spaces during drying using convective drying (moist samples)
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0
10
20
30
40
50
60
70
80
0 250 500 750 1000 1250 1500
Shri
nki
ng
(%)
Time (min)
Shrinking (determined by immersion into heptane)
Vb = bulk volume at t (cm³)Vb0= bulk volume at t=0 (cm³) Vb0= average value= 5 cm3
10010
b
bb
V
VS
dried fruits(Sb=65-70%)
Initial sample 4 hours
8 hours 12 hours20x
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Vacuum drying
T = 60 °C and P = 15mbar
Vacuum Drying
Vacuum drying of bananas was performed using a vacuum oven (Ethick Technology, 440-DE model-SP, Brazil). Banana slices (5mm) were placed evenly in a thin single layer on the drying tray and placed inside the vacuum oven.
The vacuum pressure and the drying temperature were kept constant at 15mbar and 600C.
The fruits were dried for 6h to a final moisture content of 0,0760 g/g
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0
1
2
3
4
5
0 100 200 300 400
Tru
evo
lum
e (
cm³)
Time (min)
True volumes (solid + liquid)as determined with the gas porosimeter
Vacuum Drying
1001%
b
p
V
V
0
10
20
30
40
50
60
70
80
90
0 100 200 300 400
Vo
idsp
ace
s(%
)
Time (min)
Porosity of dried fruits (70%)
Evolution of the void spaces during drying using vacuum drying (moist samples)
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10010
b
bb
V
VS
0
10
20
30
40
50
60
70
0 100 200 300 400
Shri
nki
ng
(%)
Time (min)
dried fruits (Sb=68%)
Shrinking - Vacuum Drying(determined by immersion into heptane)
Vb = bulk volume at t (cm³)Vb0= bulk volume at t=0 (cm³) Vb0= average value= 5 cm3
Initial sample 2 hours
4 hours 6 hours20x
Vacuum Drying
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Initial sample 2 hours
4 hours 6 hours
Vacuum Drying
50x
Microwave Vacuum Drying
Vacuum helps to reduce drying temperature by reducing the boiling point of water during microwave-vacuum drying.
Drying rates of carrot slices (Durance, 1999)- hot air at 70 C
- Freeze drying
- microwave-vacuum drying
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Microwave vacuum dryingExperimental device
Trapping
Vacuum pump
Digital vacuum meter
Vacuum
chamber
Microwave oven/dryer
12:00
Turntable plate
SEM - Microwave vacuum drying
Microwave vacuum drying
Drying time 19 min
Moisture 0,03 g/g
Bulk volume 2,46 cm³
Porosity 66%
Shrinking 51%
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Structural changes in banana samples during drying by KMFD
KMFD-Conductive multi-flash drying, T = 80°C
0
0,2
0,4
0,6
0,8
1
0 25 50 75 100
Wat
er a
ctiv
ity
(Aw
)
Time (min)
0,00
0,50
1,00
1,50
2,00
2,50
0 25 50 75 100 125
Mo
istu
re(g
/g)
Time (min)
KMFD
Drying curvesreproducibility
Triplicate
0,00
0,50
1,00
1,50
2,00
2,50
0 25 50 75 100 125
Mo
istu
re (
g/g
)
Time (min)
Before flash drying
After flash drying
Free water
Conductive and flash evaporation contributions
Water activity
flash evaporation is important
12 3
4
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0
5
10
15
20
25
30
35
40
0% 10% 20% 30% 40% 50% 60% 70%
Forc
e (
N)
Strain(%)
Pulse 5
Pulse 6
Pulse 7
Pulse 8
Pulse 9
Pulse 10
Pulse 11
Pulse 12
Puncture tests of fruits dried by KMFDPulse 10
aw = 0,401
Pulse 12aw = 0,240 Pulse 11
aw= 0,353
1 2 3 4 5 6 7 8 9 10 11 12
Pictures of banana slices after each KMFD cycle
0
10
20
30
40
50
60
70
80
90
0% 10% 20% 30% 40% 50% 60% 70%
Forc
e (N
)
Strain(%)
0
10
20
30
40
50
60
70
80
90
0% 10% 20% 30% 40% 50% 60% 70%
Forc
e (N
)
Strain(%)
0
10
20
30
40
50
60
70
80
90
0% 10% 20% 30% 40% 50% 60% 70%
Forc
e (N
)
Strain(%)
0
10
20
30
40
50
60
70
80
90
0 10 20 30 40 50 60 70
Forc
e (N
)
Strain(%)
Pulse 9
Pulse 12Pulse 11
Pulse 10
Puncture tests of fruits during drying by KMFD
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0
1
2
3
4
5
0 25 50 75 100 125
Tru
evo
lum
e (
cm³)
Time (min)
2
True volumes (solid + liquid)as determined with the gas porosimeter
KMFD PROCESS
1
3 45
True volumeof dried fruits
True volumeSolid matrix + liquid
0
10
20
30
40
50
60
70
80
90
0 25 50 75 100 125
Vo
idsp
ace
s(%
)
Time (min)
Porosity of dried fruits (75%)
1001%
b
p
V
V
1
3
2
5
4
6
Evolution of the void spaces during drying using KMFD (moist samples)
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0
10
20
30
40
50
0 25 50 75 100 125
Shri
nki
ng
(%)
Time (min)
Shrinking - KMFD PROCESS (determined by immersion into heptane)
10010
b
bb
V
VS
1
2
34
5 dried fruits (Sb=40%)
Vb = bulk volume at t (cm³)Vb0= bulk volume at t=0 (cm³) Vb0= average value= 5 cm3
Structural changes in banana samples during drying – KMFD