Mathematical and kinetic models were set up for heat-induced quality changes in soy milk, including inactivation of trypsin inhibitor activity (TIA) and degradation of thiamin, riboflavin, color, and flavor over a wide range of time-temperature combinations with particular interest in the ultrahigh-temperature (UHT) range. On the basis of these models, multiresponse optimization of the thermal processes for soy milk was carried out to obtain the following effects simultaneously: (1) maximum destruction of bacterial spores, (2) maximum inactivation of TIA, and (3) minimum degradation of sensory and nutritional qualities. By a suitable selection of high temperatures and extended heating times, for example, 143 °C/60 s, it is possible to use a single-step UHT process to produce a commercially sterile soy milk with satisfactory TIA inactivation, highly acceptable color and flavor, and thiamin retention between 90 and 93%. ; Department of Applied Biology and Chemical Technology