25 According to Clydesdale and Ahmed 1978, object-light interactions may
affect on color measurement of samples, such as reflection from the surface, refraction into the object, transmission through the object, diffusion, and
absorption within the object. Heating tempe in salt solution caused the increase of water content entering into the tissue. When the source light from chromameter
came on the tempe surface, it would be resulted increasing intensity of object-light interactions. In this way, increasing water content of tempe produced the more
reflected light from the tempe surface. This might increase the lightness of tempe and change the other color propeties.
The change of chroma and hue parameters corresponded to the intensity of yellowness and greenness. The elevation of hue angle was influenced by the
increase of yellowness and the decrease of greenness intensity. The chroma had almost similar value to yellowness. Hence, the reduction of greenness value did
not significantly affected on the chroma of tempe.
A food system which contain a carbonyl group of reducing sugar and an amine group of free amino acids subjected to high temperature treatment should
experience the Maillard reaction involving the formation of brown pigmen Kim and Lee 2009. It is well known that tempe contains high protein 23-55 and
also some sugars Kwon et al. 2010. When tempe was heated for certain time, the carbonyl group and amine group might interact to form brown color of Maillard
reaction. But, the presence of salt in heating medium could decrease the rate of Maillard Reaction due to the decrease of water activity value BeMiller and Huber
2008. Therefore, it can be assumed that the use of 2 salt solution as heating medium might be effectively retain the visual appearance of tempe.
4.4 Kinetic Modeling of Quality Changes
Kinetic modeling is one of the quantitative modeling used as indicators of food quality degradation. A systematic way is done to stimulate an appropriate
design process, thus the quality retention of product can be managed well Van Boekel 2008. According to Hindra and Baik 2006, the rate of quality change
strongly relates with to two main factors, product composition moisture content, water activity, pH, etc. and environmental factors time, temperature, etc..
Furthermore, kinetic order reaction is determined by the characteristics of chemical reaction in the product. Most heat induced reactions are assumed to obey
first order kinetic which the reaction rate is proportional to the reactant concentration or quality properties Holdsworth and Simpson 2007.
Determination of quality indicators induced by heating was based on a logaritmic relationship describing the quality attributes as a function of variable
process time and temperature obeying first order kinetic reaction. However, in this study not all tested properties could be modeled well as thermal kinetic
parameters because some of them were not affected significantly by process conditions, such as the total flavonoid content, hue, springiness, stickiness,
cohesiveness, and chewiness. The heat sensitive quality parameters of tempe, such as antioxidant capacity, TPC, hardness, lightness, yellowness, greenness, and
chroma, could be modeled well as first-order reaction with different tendency.
26
Figure 13 Kinetic modeling of DPPH scavenging capacity of tempe during heating at 75, 85, and 95
o
C. The effects of heating at three different temperatures 75, 85, and 95
o
C on radical DPPH scavenging capacity of tempe are shown in Figure 13. The results
of spectrophotometric analysis indicated an increase in antioxidant capacity of total of tempe-salt solution and only salt solution due to thermal treatments. In
contrast, antioxidant capacity of tempe decreased for 120 min during heating period, but the rate of decreasing antioxidant capacity in tempe increased with
increase of temperature k
75
=0.0050, k
85
=0.0051, and k
95
=0.0052 min
-1
. On the other hand, the rate of increasing antioxidant capacity in salt solution k
75
=0.0145, k
85
=0.0150, and k
95
=0.0174 min
-1
was greater than in total of tempe-salt solution k
75
=0.0025, k
85
=0.0026, and k
95
=0.0033 min
-1
. Totally the thermal treatments of tempe at 75 and 85
o
C gave almost same effects on total of tempe-salt solution for 120 min. However, heating at both of temperature was significantly different as
-0,8 -0,4
0,0 0,4
0,8 1,2
1,6 2,0
30 60
90 120
ln CtCo
Time min
Tempe
75ºC: y = -0.0050x, r² = 0.791 85ºC: y = -0.0051x, r² = 0.895
95ºC: y = -0.0052x, r² = 0.828 -0,8
-0,4 0,0
0,4 0,8
1,2 1,6
2,0
30 60
90 120
ln C
t C
o
Time min
Salt Solution
75ºC: y = 0.0145x, r² = 0.951 85ºC: y = 0.0150x, r² = 0.939
95ºC: y = 0.0174x, r² = 0.885
-0,8 -0,4
0,0 0,4
0,8 1,2
1,6 2,0
30 60
90 120
ln C
t C
o
Time min
Total of Tempe and Salt Solution
75ºC: y = 0.0025x, r² = 0.887 85ºC: y = 0.0026x, r² = 0.849
95ºC: y = 0.0033x, r² = 0.880
27 compared to at 95
o
C. It can be assumed that the rate constant of antioxidant capacity significantly changed at temperature up to 85
o
C for 120 min.
Figure 14 Kinetic modeling of total phenolic content of tempe during heating at 75, 85, and 95
o
C. The changes of total phenolic contents during heating expressed as mg of
galic acid equivalentg of sample are shown in Figure 14. When samples were subjected to the thermal processing, the TPC changed with the same trend as
antioxidant capacity showing the decrease in tempe and the increase in salt solution and total of tempe-salt solution. The rate of decreasing TPC in tempe
increased with increase of temperature k
75
=0.0034, k
85
=0.0036, and k
95
=0.0041 min
-1
. Moreover, the TPC of salt solution elevated more quickly k
75
=0.0090,
-0,5 0,0
0,5 1,0
1,5
30 60
90 120
ln CtCo
Time min
Tempe
75ºC: y = -0.0034x, r² = 0.809 85ºC: y = -0.0036x, r² = 0.954
95ºC: y = -0.0041x, r² = 0.888 -0,5
0,0 0,5
1,0 1,5
30 60
90 120
ln CtCo
Time min
Salt Solution
75ºC: y = 0.0090x, r² = 0.908 85ºC: y = 0.0111x, r² = 0.878
95ºC: y = 0.0134x, r² = 0.805
-0,5 0,0
0,5 1,0
1,5
30 60
90 120
ln C
t C
o
Time min
Total of Tempe and Salt Solution
75ºC: y = 0.0029x, r² = 0.778 85ºC: y = 0.0043x, r² = 0.953
95ºC: y = 0.0051x, r² = 0.910
