Effects of Toasting Time on Digestive Hydrolysis of Soluble and Insoluble 00‑Rapeseed Meal Proteins

Abstract

Thermal damage to proteins can reduce their nutritional value. The effects of toasting time on the kinet ics of hydrolysis, the resulting molecular weight distribu tion of 00-rapeseed meal (RSM) and the soluble and insolu ble protein fractions separated from the RSM were studied. Hydrolysis was performed with pancreatic proteases to rep resent in vitro protein digestibility. Increasing the toasting time of RSM linearly decreased the rate of protein hydroly sis of RSM and the insoluble protein fractions. The extent of hydrolysis was, on average, 44% higher for the insolu ble compared with the soluble protein fraction. In contrast, the rate of protein hydrolysis of the soluble protein fraction was 3–9-fold higher than that of the insoluble protein frac tion. The rate of hydrolysis of the insoluble protein frac tion linearly decreased by more than 60% when compar ing the untoasted to the 120 min toasted RSM. Increasing the toasting time elicited the formation of Maillard reac tion products (furosine, Nε -carboxymethyl-lysine and Nε - carboxyethyl-lysine) and disulfide bonds in the insoluble protein fraction, which is proposed to explain the reduction n the hydrolysis rate of this fraction. Overall, longer toast ing times increased the size of the peptides resulting after hydrolysis of the RSM and the insoluble protein fraction. The hydrolysis kinetics of the soluble and insoluble protein fractions and the proportion of soluble:insoluble proteins in the RSM explain the reduction in the rate of protein hydrol ysis observed in the RSM with increasing toasting time.