Losses in Available Lysine During Thermal Processing of Soy Protein Model Systems

This study was conducted in order to develop a mathematical model for predicting lysine losses during processing of soy products. Model systems used in this study consisted of micro crystalline cellulose, glucose, sucrose, potato starch and soy protein. System composition, water activity, pH and time and temperature of heating were varied and available lysine was monitored by the fluoro‐2,4‐dinitro benzene method of Carpenter. In the first set of experiments, statistical analysis of the data obtained resulted in an equation which shows the effects of the variables used on available lysine retention: Fraction available lysine remaining = 0.58 + 0.047 pH ‐ 0.093 glucose ‐ 0.059 temperature —0.0068 time + 0.031 (water activity) 2 + 0.025 a w sucrose + 0.033 sucrose starch. These data were collected at heating times well in excess of that required to destroy all reducing sugars present. Heating times were reduced in the second experiments such that kinetic data could be obtained. The average E a was 28,500 calories/mole°K and the average reference reaction rate at 100°C (K 100 ) was 0.036 mg lysine/min.