1. VACUUM FRYING PROCESSING TECHNOLOGY IMPROVES QUALITY
ATTRIBUTES OF FRIED SWEETPOTATO CHIPS
1Esan, T.A., 1,*Sobukola, O.P., 1Sanni, L.O. and 2Bakare, H.A.
1Department of Food Science and Technology, Federal University of Agriculture, P.M.B. 2240, Abeokuta, Nigeria
2Department of FoodService and Tourism, Federal University of Agriculture, P.M.B. 2240, Abeokuta, Nigeria
*Corresponding Author: olajidephilip@yahoo.com/sobukolaop@unaab.edu.ng
1

2. Introduction
Sweetpotato (Ipomoea batatas) is a dicotyledonous plant
that belongs to the family Convolvulaceae
The yellow flesh varieties is high in carbohydrates, vitamin A,
and produces more edible energy per hectare per day than
wheat, rice or cassava.
Snack foods especially the fried foods is enjoying an ever
increasing popularity world-wide (SFA, 1997; Brinkmann,
2000);
The frying technology is important to many sectors of the
food industry: suppliers of oil and ingredients; food service
operators; the food industries, and manufacturers of
equipment;
2

3. Core
Crust
Heat and mass transfer during atmospheric deep-fat frying
Structural oil
Penetrated
surface oilSurface oil

4. Microstructural changes during atmospheric deep fat frying
Atmospheric conditions High temperatures
Key structural
components changes
Starch
dehydration
Water
vaporization
Moisture
loss
Crust
Core
Beneficial
compounds
degradation
Non-enzymatic
browning
reactions
Frying oil
hydrolisis
Frying oil thermal
degradation
Frying oil
oxidation
Oil uptake

5. What is the problem?
Temperature and oxygen affects the quality of
atmospheric fried products and oil
Solution
Vacuum frying (VF) to design novel snacks
What do we need?
Development of a vacuum frying system
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6. New processing technology: Vacuum inclusion
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7. Vacuum frying operations
vacuum
pump
Depressurization: Patm → Pvac
T oil = T frying
Frying
Pressurization: Pvac → Patm
PV(T)
surface oil layer
air
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8. Hypothesis
By reducing the frying pressure, (vacuum deep-fat
frying), it is possible to remove product moisture in a
low-oxygen environment at a low temperature (due
to water boiling-point depression), allowing to
produce low fat and nutritious novel snacks, such as
SP chips, while keeping unique characteristics of
regular fried snacks.
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9. Main objective
Study the effect of vacuum inclusion in a traditional
deep-fat frying operation, in order to understand its
impact in the developed microstructure and
associated transport phenomena, particularly oil
uptake, as well as in the main quality parameters of
fried SP chips.
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10. MATERIALS
Three varieties of YFSP were procured from local market
in Abeokuta, Nigeria:
EX-OYUNGA
442016
SPK004
Three different types of frying oils normally used for
frying were purchased from a local market in Abeokuta:
Refined bleached deodorized oil (RBDO)
Palm oil (PO)
Groundnut oil (GO)
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11. Frying Operations
Table1: The coded values of the independent variables for vacuum
frying of cassava roots
Codes
Variable -1 0 +1
X1 EX-OYUNGA 440216 SPK004
X2 RBDO PO GO
X3 (oC) 108 122 136
X4 (cmHg) 4.91 9.91 19.91
X5 (min) 3 6 9
X1, X2, X3, X4 and X5 are SP variety, types of oil, frying temperature, vacuum pressure
and frying time, respectively
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12. Manometer
Frying
vessel
Condenser Pressure
release
valve
Temperature
controller
Vacuum frying machine donated by International
Foundation for Science (IFS)7/3/2013 12

13. Sample Analysis
Oil and moisture contents of fried SP chips (AOAC,
2003)
Colour parameters – (Glories, 1984)
Carotenoid content of raw and fried YFC chips (AOAC,
2005)
Texture (Garaya and Moreira, 2002)
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14. RESULTS AND DISCUSSION
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15. 7/3/2013 15
Experimental
Run Oil Moisture β-Carotene Texture Lightness Redness Yellowness
(%) (%) (ppm) (N)
Values are means of duplicate
1 16.38 2.10 53.37 6.9 26.58 0.84 71.88
2 13.72 1.76 4.89 5.75 1.04 74.25 23.88
3 17.07 2.12 82.74 9.50 32.53 10.87 56.33
4 17.10 4.27 60.79 14.00 2.02 69.57 27.96
5 11.33 2.45 48.32 8.65 27.96 1.37 69.86
6 17.83 1.85 62.21 5.05 26.58 31.23 41.96
7 9.93 3.07 54.79 3.25 26.33 1.26 71.54
8 16.99 1.66 1.89 3.15 1.96 71.37 25.97
9 7.51 2.85 68.21 20.55 31.24 42.37 25.65
10 19.32 1.87 80.69 4.90 19.93 22.71 56.78
11 10.85 2.14 75.48 9.45 28.12 1.45 70.03
12 17.34 1.94 86.06 7.10 25.91 1.16 72.62
13 6.93 2.94 71.85 8.60 41.27 35.96 21.95
14 7.10 1.97 87.95 4.90 62.60 7.19 29.87
15 10.92 2.07 75.32 15.00 34.95 3.02 61.66
16 18.30 2.17 104.69 5.60 38.26 2.96 57.97
17 16.16 2.07 69.00 5.90 39.64 1.87 57.94
18 17.00 1.83 72.16 7.80 4.52 67.84 27.48
19 17.29 1.77 94.58 12.20 1.76 71.27 25.56
20 18.60 2.13 103.27 10.40 1.84 38.74 58.63
21 17.58 1.68 96.64 6.35 26.30 0.64 72.83
22 5.36 7.25 66.16 5.15 58.31 9.86 31.14
23 10.41 2.05 82.89 6.60 26.05 1.04 72.74
24 15.20 1.94 107.85 9.45 1.78 39.86 58.33
25 17.83 2.38 109.90 4.45 23.86 11.26 63.96
26 8.17 5.84 71.37 1.87 72.40 24.96
27 15.00 1.93 8.53 3.65 1.74 73.84 23.96
28 15.80 2.25 72.48 12.85 26.09 0.91 72.97
Table 1. Response surface Analysis result of responses as a function of the independent variables

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*Significant at 5% level
A, B, C, D and E are frying temperature, vacuum pressure, frying time, SP variety and type of frying oil
Parameters Oil Moisture β-Carotene Texture Lightness Redness Yellowness
Intercept 9.85 1.78 81.68 7.15 23.23 14.69 61.66
A -0.02 -0.50 -15.68* 1.37 -11.38* 20.04* -9.63
B 0.23 -0.42 - 2.90 1.19 0.66 -11.25 10.56
C 0.85 -1.08 -13.74* 2.29* -11.57* 14.61 -2.90
D 0.77 -0.23 -4.47 -1.73* 5.58 -7.91 2.43
E 1.07 0.01 3.58 -2.08* -4.65 2.06 2.48
A2 -1.34 0.45 -44.31* -4.70* -2.07 34.28* -32.28*
B2 0.57 0.46 2.68 -0.85 2.23 -3.58 1.29
C2 0.13 -0.33 11.62 0.04 -5.01 12.35 -7.56
D2 0.15 0.27 17.99 2.02 -6.65 0.83 5.69
E2 -2.89 0.17 -3.68 4.22* 6.83 -17.17 10.55
AB 0.16 0.29 11.57* 0.69 9.26 -2.60 -6.84
AC -0.57 0.08 -4.30 -1.66 -0.61 4.56 -4.09
AD 1.01 0.40 -13.46* -0.30 -2.56 -0.65 3.15
AE -0.46 0.54 3.84 -3.27* 8.11 -9.91 1.69
BC 0.51 0.71 16.45* -2.96* 0.27 3.20 -3.60
BD -0.14 0.18 -14.71* -0.56 -1.08 -1.79 2.79
BE -0.68 0.06 1.83 0.07 9.16* -11.99 2.79
CD -1.34 0.50 -11.28* -3.55* 11.19* -9.20 -2.13
CE 1.14 0.25 -8.32 2.45* 1.05 -0.72 -0.56
DE -0.44 -0.09 8.37 -0.03 6.06 -5.97 0.0012
R2 0.76 0.72 0.95 0.95 0.89 0.91 0.875
PRESS 2209.46 1380.80 37000.23 3415.56 48307.68 200000 95030.57
F value 1.75 0.89 6.80 5.51 2.89 3.34 2.46
Table 4. Regression coefficients for the quadratic models for all the responses

17. 17
15.4973
16.1583
16.8192
17.4802
18.1411
Oilcontent
108.00
115.00
122.00
129.00
136.00
6.54
11.54
16.54
21.54
26.54
A: Frying Temperature
B: Vacuum pressure
Oil content
A: Fry ing Temperature
B:Vacuumpressure
108.00 115.00 122.00 129.00 136.00
6.54
11.54
16.54
21.54
26.54
15.938
16.3786
16.3786
16.8192 16.8192
17.2599
17.7005
22
1.60721
2.17901
2.7508
3.3226
3.8944
Moisturecontent
108.00
115.00
122.00
129.00
136.00
6.54
11.54
16.54
21.54
26.54
A: Frying Temperature
B: Vacuum pressure
Moisture content
A: Fry ing Temperature
B:Vacuumpressure
108.00 115.00 122.00 129.00 136.00
6.54
11.54
16.54
21.54
26.54
1.98841
2.3696
2.7508
3.132
3.5132
22
Fig. 1. Response surface and contour plots for moisture and oil contents of fried sweetpotato chips

18. 18
15.6903
34.6283
53.5663
72.5043
91.4423
BetaCarotene
108.00
115.00
122.00
129.00
136.00
6.54
11.54
16.54
21.54
26.54
A: Frying Temperature
B: Vacuum pressure
Beta Carotene
A: Fry ing Temperature
B:Vacuumpressure
108.00 115.00 122.00 129.00 136.00
6.54
11.54
16.54
21.54
26.54
28.3156
40.9409
53.5663
53.5663
66.191666.1916
78.817
78.817
22
-0.26368
1.74021
3.7441
5.74799
7.75188
Texture
108.00
115.00
122.00
129.00
136.00
6.54
11.54
16.54
21.54
26.54
A: Frying Temperature
B: Vacuum pressure
Texture
A: Fry ing Temperature
B:Vacuumpressure
108.00 115.00 122.00 129.00 136.00
6.54
11.54
16.54
21.54
26.54
1.07225
2.40817
2.40817
3.7441
3.7441
5.08003 5.08003
6.41596
22
Fig. 2. Response surface and contour plots for Beta carotene and texture of fried sweetpotato chips

19. 19
3.0816
12.9044
22.7272
32.55
42.3728
Lightness
108.00
115.00
122.00
129.00
136.00
6.54
11.54
16.54
21.54
26.54
A: Frying Temperature
B: Vacuum pressure
Lightness
A: Fry ing Temperature
B:Vacuumpressure
108.00 115.00 122.00 129.00 136.00
6.54
11.54
16.54
21.54
26.54
9.63012
16.1787
22.7272
29.2757
35.8242
22
-2.2911
18.0985
38.488
58.8775
79.2671
Redness
108.00
115.00
122.00
129.00
136.00
6.54
11.54
16.54
21.54
26.54
A: Frying Temperature
B: Vacuum pressure
Redness
A: Fry ing Temperature
B:Vacuumpressure
108.00 115.00 122.00 129.00 136.00
6.54
11.54
16.54
21.54
26.54
11.3019
24.895
24.895
38.48852.081
65.6741
22
Fig. 3. Response surface and contour plots for Lightness and redness of fried sweetpotato chips

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17.3168
31.8758
46.4349
60.9939
75.5529
Yellowness
108.00
115.00
122.00
129.00
136.00
6.54
11.54
16.54
21.54
26.54
A: Frying Temperature
B: Vacuum pressure
Yellowness
A: Fry ing Temperature
B:Vacuumpressure
108.00 115.00 122.00 129.00 136.00
6.54
11.54
16.54
21.54
26.54
27.0228
36.7288
36.7288
46.4349
46.4349
56.1409
65.8469
22
Fig. 4. Response surface and contour plots for yellowness of fried sweetpotato chips

21. 7/3/2013
21
0
0.5
1
1.5
2
2.5
3
3.5
4
Atmospheric Optimized Vacuum
Moisturecontent(%)
0
1
2
3
4
5
6
7
8
9
10
Atmospheric Optimized Vacuum
Oilcontent(db)
0
20
40
60
80
100
120
Atmospheric Optimized Vacuum
BetaCarotene(ppm)
0
2
4
6
8
10
12
Atmospheric Optimized Vacuum
Texture(N)
Fig. 5. Comparison of atmospheric and optimized vacuum fried SP chips

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0
5
10
15
20
25
30
35
40
45
Atmospheric Optimized Vacuum
Lightness(L*)
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
2
Atmospheric Optimized Vacuum
Redeness(a*)
69.5
70
70.5
71
71.5
72
72.5
73
73.5
Atmospheric Optimized Vacuum
Yellowness(b*)
Fig. 6. Comparison of colour properties of atmospheric and optimized vacuum fried SP chips

23. Key findings
In terms of the basic deep fat frying qualities:
Vacuum fried SP chips retains more carotenoid than
atmospheric fried samples after processing
Colour properties of vacuum fried samples are better
than the atmospheric fried samples
Vacuum fried samples are more crispier than
atmospheric fried samples
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24. Acknowledgement
International Foundation for Science (IFS)
K + S Kali GmbH for full sponsorship of
the corresponding author to APA 2013
24Optimized vacuum fried SP crisps Atmospheric fried SP crisps

25. MANY THANKS FOR YOUR
ATTENTION
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