| Abstrakt: |
Dielectric heating at frequencies of 42 and 2450 MHz was applied to whole soybeans of natural moisture content for varies exposure times. The minimum energy absorbed (MEA) was calculated from moisture-loss and temperature-elevation data. Biochemical analyses were performed to determine protein dispersibility index (PDI), nitrogen solubility index (NSI), and trypsin-inhibitor, urease, lipoxygenase, and peroxidase activities. Because the heating rates were different at the two frequencies for the power levels used, plots of the biochemical properties against temperature of exposure time showed an apparent frequency dependence. This dependence on frequency disappeared, however, when MEA was substituted as the independent variable. Chemical analyses revealed that dielectric heating of soybeans at natural moisture levels should be as effective as conventional steam toasting in reducing trypsin-inhibitor activity. PDI and NSI, but not urease, were suitable indicators of trypsin-inhibitor inactivation by dielectric heating. Lipoxygenase was completely inactivated by the dielectric-heating treatments that gave suitable trypsin-inhibitor inactivation, but peroxidase activity remained relatively high, offering possible advantages for bleaching and improved soy product color. |
