Antioxidant in Tempe Kinetika Perubahan Kapasitas Antioksidan dan Mutu Fisik Tempe Selama Pemanasan

7 soybean Gandhi and Bourne 1991, Xu and Chang 2008 b , tempe Handoyo and Morita 2006. Thermal softening can be due to changes in cell wall matrix polysaccharides celluloses, hemicelluloses, pectins etc. which depend on many factors such as pH, types and amounts of various salts present in the plant cell wall. Water uptake by polysaccharides results in reduction of cohesiveness of cell wall matrix thereby resulting in lower adhesion. Other reason for softening is due to loss of turgor pressure which is pressure of cell components against the cell wall and it is due to the water content inside the cell Lund 1982. The thermal treatments can result in plasmolysis which reduces the turgor pressure and it is responsible for softening of food Rao and Lund 1986. Thermal processing influences the nutritional value of some food products by changing the total of antioxidant capacity. Boiled and steamed eclipse black beans exhibited significantly lower antioxidant activities than raw beans in total phenolic content TPC, DPPH free radical scavenging activity DPPH, and oxygen radical absorbing capacity ORAC Xu and Chang 2008 a . As compared to the raw soybeans, all processing methods caused significant decreases in TPC, DPPH, ORAC, total flavonoid content TFC, condensed tannin content CTC, monomeric anthocyanin content MAC, and ferric reducing antioxidant power FRAP, and in black soybeans Xu and Chang 2008 b . In the other hand, thermal processing elevated total antioxidant activity and bioaccessible lycopene content in tomatoes and produced no significant changes in TPC and TFC. The increase in total antioxidant activity of the heat- processed tomatoes was due to the increased amount of lycopene as a major phytochemical in tomatoes and other bound phytochemicals released from the cell matrix Dewanto et al. 2002. However, high pressure processed tomato and carrot purées had significantly higher antioxidant capacities when compared to thermally treated samples Patras et al. 2009.

2.6 Kinetics of Quality Degradation

Some of quality degradation reaction in food product can be described well by first order kinetic reaction. This model was characterized by a straight line when the logarithm of the texture property was plotted against heating time Rizvi and Tong 1997. Generally, thermal softening in fruits and vegetables was suited to the first order rate with the firmness as the primary texture attribute Rao and Lund 1986, Bourne 1987, Rizvi and Tong 1997 . The heat-induced degradation of natural pigments and browning reaction also followed the first order reaction Villota and Hawkes 2007. The equations for a degradation reaction for first order are Van Boekel 2008: - dC dt =kC -ln C C =kt