Effect of thermal processing on available lysine, thiamine and riboflavin content in soymilk

Soymilk was heated over a range of temperatures (90-140 degrees C) and times (0-6 h). The available lysine, thiamine and riboflavin content of the soymilk samples were determined. There was no significant change in available lysine during a 3 h heating period at 95 degrees C. At elevated temperatures of 120 and 140 degrees C, optimum heat processed soymilk gave higher measured values of available lysine than did soymilk processed at 95 degrees C. Prolonged heating at 120 and 140 degrees C caused a decline in available lysine. Kinetic data on the thermal degradation of thiamine and riboflavin in soymilk were fitted with first-order kinetics and the kinetic parameters were determined. (C) 1998 SCI.