15
4 RESULTS AND DISCUSSION
4.1 Determination of Lag Time
The heat transfer of tempe took place from water waterbath heating medium to salt solution through the vial glass surface. Convection heat transfer
was at the outside and inside surface of the vial and conduction was through the vial wall. Then, the heat traveled through the 2 of salt solution to the tempe
surface via convection and furthermore, the conductive heat transfer took place from the surface to the center of tempe.
Figure 6 shows the heating profiles recorded at 75, 85, and 95
o
C in the cold spot of the vial. Measurement of the lag time was to ensure the isothermal
condition of heating. It can be seen from the experimental data gathered that the temperature profiles of tempe center lagged during heating at three different
temperature which it was needed heating time of 6 min to achieve the targeted heating temperature of 75
o
C, whereas at 85 and 95
o
C the lag time was 7 min.
Figure 6 Heating profiles of tempe center at 75, 85, and 95
o
C.
4.2 Effects of Heating on Antioxidant Properties
4.2.1 Antioxidant Capacity
The DPPH assay measures against the 2,2-diphenyl-1-picryhydrazyl radical which is reduced to the yellow coloured in alcoholic solution in the
presence of a hydrogen-donating antioxidant due to the formation of the non- radical form DPPH-H Gülçin 2012. The fresh tempe used in this study had
antioxidant capacity of 2.00 mM of AAEg see Table 3. The effect of heating at three different temperatures 75, 85, and 95
o
C on radical DPPH scavenging capacity of fresh tempe is shown in Figure 7.
Heating samples increased the total amount of antioxidant capacity in total of tempe-salt solution. The increase of
antioxidant power also occured only in salt solution, whereas antioxidant capacity decreased in tempe during heating period of 120 min.
20 40
60 80
100
10 20
30 40
50 60
T em
pera ture
o
C
Time min
75ºC 85ºC
95ºC
16 A similar pattern had been reported for ultra high temperature UHT
process of soymilk Xu and Chang 2009, pasteurization of tea extracts Manzocco et al. 1998, and steaming of several vegetables such as carrots,
spinach, mushrooms, asparagus, broccoli, cabbage, red cabbage, green and red peppers, potatoes and soybeans Halvorsen et al. 2006, which showed an increase
in the antioxidant capacity. The steaming process significantly increased about 75- 140 DPPH values of antioxidant capacity in yellow soybeans as compared to the
raw soybeans Xu and Chang 2008.
Table 3 Characteristics of fresh tempe
a
. Parameters
Unit Value
Antioxidant capacity mM of AAEg
2.00 ± 0.03 Total phenolic content
mg of GAEg 1.45 ± 0.01
Total flavonoid content mg of CAEg
0.77 ± 0.04 Hardness
kg 1.19 ± 0.04
Springiness -
0.38 ± 0.01 Stickiness
- 0.21 ± 0.02
Cohesiveness -
0.22 ± 0.01 Chewiness
- 0.14 ± 0.01
Lightness -
64.00 ± 0.05 Greenness
- -0.30 ± 0.01
Yellowness -
3.69 ± 0.03 Chroma
- 3.70 ± 0.03
Hue -
-88.93 ± 0.09
a
Data are expressed as average ± standard error of mean SEM.
According to Sheih et al. 2000 that two-thirds of antioxidant capacity in tempe was contributed by peptides. Tempe containted 17 amino acids Kwon et al.
2010, which tyrosine, phenylalanine, cysteine, lysine, arginine, aspartate, glutamate, histidine, glycine and proline were suggested playing important role in
antioxidant power of soybean Chen et al. 1996, Fang et al. 2002, Hu et al. 2003, Je et al. 2004, Rajapakse et al. 2005, Riison et al. 1980 Saiga et al. 2003.
Soybean protein isolate conducted denaturation at 76.5
o
C with high water content Kitabatake et al. 1990. However, antioxidant capacity of protein and amino
acids was relatively constant during thermal treatments Arcan and Yemeniciog˘lu
2007. Isoflavones in soybean have been considered to be the source of
antioxidant. Genistein, daidzein, and their glycosides had a radical DPPH scavenging power, ferric reducing-antioxidant power FRAP, and suppression of
low-density lipoprotein LDL oxidation Lee et al. 2005. Heating soybean product at 70-90
o
C caused degradation of glucoside isoflavones to aglycone form Eisen et al. 2003 which the aglycones had stronger antioxidant capacity than the
glucosides Hayes et al. 1977, Pratt and Stafforini 1979. As compared to raw soybean, boiled yellow soybean had significant increases of
β-glucoside daidzin, glycitin, and genistin and aglycone daidzein, glycitein, and genistein
17 isoflavones, but significantly decreased the content of the malonylglucoside forms
malonyldaidzin, malonylglycitin, and malonylgenistin Xu and Chang 2008. Therefore, this research indicated that isoflavones from phenolic group obtained
from 80 acetone extract were the responsible components affecting the changes of antioxidant capacity of tempe during heating.
On the other hand, the decline of antioxidant compounds in tempe was due to the increase of water soluble antioxidant subtances to 2 of salt solution.
Thermal process might decrease firmness and adhesion of cell walls Van Buren 1979, thus it induced releasing bound phenolic compounds, such as flavonoids,
accumulated in the vacuoles Brecht et al. 2008. Briefly, as longer heating time and higher temperature, the bound antioxidant components were more liberated
from cell and leached into salt solution.
Figure 7 Effects of heating on DPPH scavenging capacity of tempe at 75, 85, and 95
o
C.
0,00 1,00
2,00 3,00
4,00
30 60
90 120
DP P
H sca
v en
g in
g ca
p a
ci ty
m M
AA Eg
Time min
Tempe
75ºC 85ºC
95ºC 0,00
1,00 2,00
3,00 4,00
30 60
90 120
DPPH sc a
v en
g in
g c
a p
a city
m M
o f
AA Eg
Time min
Salt Solution
75ºC 85ºC
95ºC
0,00 1,00
2,00 3,00
4,00
30 60
90 120
DPPH sc a
v en
g in
g c
a p
a city
m M
AA Eg
Time min
Total of Tempe and Salt Solution
75ºC 85ºC
95ºC
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