31 capacity of tempe. A positive value of E
a
means that the reaction rate increases with increasing temperature. The information from Arrhenius parameters can be
used to optimize thermal process and maximize quality retention of tempe by choosing an appropriate time-temperature combination.
Table 5 Activation energy for antioxidant properties and physical quality of tempe during thermal treatments.
Parameters Component
Equations r²
Ea kJmol
Antioxidant capacity
Tempe y = -251.1x
– 4.5769 0.999
2.09 Salt solution y = -1160.3x
– 0.9188 0.873 9.65
Total y = -1765.4x
– 0.952 0.842
14.68 Total phenolic
content Tempe
y = -1194.1x – 2.2653 0.945
9.93 Salt solution y = -2549.3x + 2.6167
0.999 21.19
Total y = -3627.2x + 4.6135
0.957 30.16
Hardness Tempe
y = -5330.3x + 10.467 0.968
44.32 Lightness
Tempe y = -6612.4x + 11.453
0.968 54.98
Greenness Tempe
y = -21823x + 58.122 0.868
181.44 Yellowness
Tempe y = -9952.8x + 22.787
0.978 82.75
Chroma Tempe
y = -8894.3x + 19.892 0.985
73.95
4.6 Application of Kinetic Data
Design of optimal thermal processing relies on kinetic of bacterial inactivation and quality changes Van Loey et al. 1995.
The destruction of microorganisms and quality factors does not proceed at the same rate Stumbo 1973,
Holdsworth 1985.
Commonly, every 10
o
C rise in temperature the rate of chemical reaction elevates two-fold, while the rate of microbial destruction rises ten-fold or
in other words quality deterioration is less heat sensitive than microbial destruction Holdsworth 1985. Because of the differences in thermal behaviour
between safety and quality factors, optimization is required to ensure the product safety and maximize retention of quality attributes.
A conventional thermal process blanching, pasteurization, and sterilisation often leads to undesirable changes in food quality, such as color,
texture, flavor, nutrition, and functionality Ndiaye et al. 2009. An accurate kinetic data of microbial inactivation and quality loss can be applied to estimate
the effects of time-temperature process on product quality desired. Heating
at higher temperatures is relatively lower destruction of quality factors. In addition,
when the heat transfer rate is enhanced then the process will be shorter resulting in lesser destruction in quality factors and this forms HTST High Temperature Short
Time concept Rattan 2012.
Figure 18 illustrates the application of kinetic parameters of tempe to determine the appropriate time-temperature combination during thermal process.
Tempe belongs to low acid food products, thus the thermal process considers both public health Clostridium botulinum and spoilage thermophilic organisms
32 Bacillus stearothermophillus to achieve commercial sterility condition. Because
of kinetic data obtained at temperature 100
o
C, extrapolation of the data at higher temperature is required for this simulation. The red dash line performs minimum
heating time required to kill 12 decimal of C. botulinum type A and B which has D
250
=0.21 min and z=17.8
o
F, whereas the blue one is minimum requirement for destruction 9 decimal of B. stearothermophillus having D
250
=4.0 min and z=12.6
o
F Lund 1975.
Key: AC= antioxidant capacity, TPC= total phenolic content, h= hardness, L= lightness, G= greenness, Y= yellowness, C= chroma, T= tempe, S= salt solution, TS= total of tempe and salt
solution.
Figure 18 Application of kinetic data in sterilization and pasteurization process.
1 10
100 1000
60 80
100 120
140 160
T im
e m
in
Temperature ºC
Antioxidant Properties
AC T AC S
AC TS TPC T
TPC S TPC TS
B. stearothermophilus C. botulinum type A B
C. botulinum type E
1 10
100 1000
60 80
100 120
140 160
T im
e m
in
Temperature ºC
Physical Quality
H T L T
G T Y T
C T B. stearothermophilus
C. botulinum type A B C. botulinum type E
33 For this simulation the process was designed to experience 10
destruction of antioxidant properties and physical quality. The example of process calculation is given in Appendix 4. Depending on the graphs, to obtain
commercial sterility product, tempe should be heated on the right side of the red dash line to fullfill a minimum “botulinum cook” F
o
=12x0.21=2.52 min. In addition, canning food industries consider the other heat resistant spores
generally referred to as thermophiles, such as B. stearothermophillus, that have the potential to cause spoilage and economic losses Awuah et al. 2007.
Therefore, to achieve safety quality of the product, tempe has to be subjected to thermal processing in the grey area.
A conventional canning process is commonly conducted at temperature ranging 110-121.1
o
C Hariyadi 2014 for a long time to destroy microorganisms of public health and spoilage concerns. Therefore, it leads to induce permanent
changes to the nutritional and sensory attributes of products. It can be seen from the graphs that heating tempe in the grey region resulted in destruction of textural
and color attributes significantly. However, the antioxidant capacity of tempe can be retained when tempe is heated for short time 11 min in the grey area.
Heating tempe at mild temperature below 100
o
C pasteurization might be alternative process to retain better antioxidant profiles and physical quality of
tempe. This simulation uses C. botulinum type E as target microbe having D
185
=0.28 min and z=16
o
F which is considered to be target pathogen of pasteurized fish and fishery products because this pathogens will survive the
pasteurization process and grow under normal storage conditions FDA 2011, Méndez and Abuín 2006. Furthermore, tempe is identical product to pasteurized
fish both of which are source of protein and has pH 4.5 low acid canned food, LACF and water activity 0.85.
According to FDA 2011, a reduction of six decimal level of C. botulinum type E is suitable 6D process for pasteurization. Because the process is not
severe enough to kill C. botulinum, the pasteurized foods require refrigeration immediately after processing. Consequently the pasteurized products are reduced
oxygen packaged e.g., vacuum packaged or modified atmosphere packaged and have limited shelf life in the distribution chain Ahmed and Shivare 2006.
It can be seen from the graphs that the green dash line performs minimum heating time required to destroy 6 decimal of C. botulinum, thus pasteurized
tempe should be heated on the right side of the green dash line. When tempe is subjected to termal processing at time-temperature combination in this area, the
minimum 10 destruction of antioxidant properties and physical quality in solid and salt solution are achievable. In this case the quality attributes of tempe during
pasteurization can be relatively retained.
Ristanti 2010 has reported that pasteurization process P
185 16
= 37 min could extend the shelf life of tempe untill 25 days in vacuum pacakages of
aluminium foil and stored at 5
o
C. However, this process effectively killed the moulds of tempe but the heat resistant microoganisms was still alive causing
spoilage of the product. Protease from spoilage organisms degraded protein into micromolecules, such as amino acids, ammonia NH
3
, and hydrogen sulfide H
2
S resulting in undesirable appearance and odor of tempe.
