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
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