Total Phenolic Content Effects of Heating on Antioxidant Properties

20 in heating of tomatoes at 88 o C for 2, 15, and 30 min, which resulted no significant changes in the total flavonoid content Dewanto et al. 2002. The results of correlation analysis see Table 4 indicated that no significant correlations existed between total flavonoid content and DPPH scavenging capacity p 0.05 except tempe at 85 and 95 o C. Figure 9 Effects of heating on total flavonoid content of tempe at 75, 85 and 95 o C. In the other hand, Xu and Chang 2009 have studied that traditional stove cooking increased by 20-23 TFC, steam injection cooking increased by 28-65 TFC, direct Ultra High Temperature UHT processing increased by 48-90 TFC, and indirect UHT processing increased by 74-113 TFC. The effects of heating at different temperature on changes of TFC in this research can not be observed distinctly. The spectrophotometric method used were less sensitive to analyze the changes of TFC during thermal treatments. The flavonoid compounds were poorly occuring in yellow soybean Xu and Chang 2007, thus the more sensitive 0,00 0,30 0,60 0,90 1,20 1,50 30 60 90 120 To ta l fla v o n o id c o n te n t m g o f C A Eg Time min Tempe 75ºC 85ºC 95ºC 0,00 0,30 0,60 0,90 1,20 1,50 30 60 90 120 To ta l fla v o n o id c o n te n t m g o f C A Eg Time min Salt Solution 75ºC 85ºC 95ºC 0,00 0,30 0,60 0,90 1,20 1,50 30 60 90 120 To ta l fla v o n o id c o n te n t m g of C A Eg Time min Total of Tempe and Salt Solution 75ºC 85ºC 95ºC 21 methods were required to study the trend of changes in total flavonoid components, such as High Performance Liquid Chromatoraphy HPLC. The predominant flavonoid compounds in soybean are isoflavones which its retention and distribution were significantly affected by thermal processing Xu and Chang 2008, Xu and Chang 2009. Although the TFC in this study was relatively constant, the antioxidant capacity from 80 acetone extract elevated during heating at 75, 85, and 95 o C see Figure 7. These findings indicated that thermal treatments transformed some compounds which had lower antioxidant status to higher antioxidant power Xu and Chang 2009. The aglycone forms of isoflavones had stronger antioxidant capacity than the glucosides Hayes et al. 1977, Pratt and Stafforini 1979. 75 o C 85 o C 95 o C Figure 10 Force versus time curves of texture profile analysis during thermal treatments of tempe.