Procedures for measuring the quality of heat-treated soybeans

Soybeans were subjected to 12 heat treatments, differing in temperature and steeping (conditioning) time: control (no heat); 110 degrees C, 0 min; 110 degrees C, 30 min; 123 degrees C, 0 min; 123 degrees C, 30 min; 135 degrees C, 0 min; 135 degrees C, 30 min; 146 degrees C, 0 min; 146 degrees C, 15 min; 146 degrees C, 30 min; 153 degrees C, 30 min; and 160 degrees C, 30 min. These soybean treatments were tested for protein dispersibility index, absorbance at 420 nm, ADIN, pepsin-insoluble N, and in situ and in vitro protein degradation. Seven of these treatments (control; 123 degrees C, 30 min; 135 degrees C, 0 min; 135 degrees C, 30 min; 146 degrees C, 0 min; 146 degrees C, 30 min; and 153 degrees C, 30 min) were used in a feeding study involving 21 Holstein heifers (7 x 7 Latin square design replicated three times) and a lactation experiment (7 x 7 Latin square design replicated two times) using 14 multiparous Holstein cows in early lactation. Concentrations of branched-chain AA in blood plasma were used as indicators of protein uptake from the intestine in the heifer study, and production of 3.5% FCM was used to evaluate soybean treatments in the lactation study. Based on the criteria used, soybeans heated to 146 degrees C for 30 min were considered to be optimal. The protein dispersibility index and absorbance at 420 nm proved useful in evaluation of heat exposure of soybeans, and these procedures are suggested for routine monitoring of quality of commercially heated soybeans.