Note. Hydrolysis of Onion and Kinetics of Non-enzymatic Browning of its Hydrolysate

Enzymatic hydrolysis of onion was performed by three different commercial enzyme products (Econase, Rapidase and Viscozyme) for preparation of onion hydrolysates. The hydrolysis yield was determined through the analysis of reducing and total sugar contents in final hydrolysates. Total sugar contents after 2 h-hydrolysis with Econase, Rapidase and Viscozyme were 59.6, 64.1 and 62.2mg/mL, respectively, and reducing sugar contents of 28.5, 42.7 and 35.9mg/mL in the same order. According to these results Rapidase was more suitable for the hydrolysis of onion than the other enzymatic products. The effect of temperature on non-enzymatic browning reaction kinetics of the onion hydrolysate was determined. The browning index variation was adequately described by both the first- and the zero-order kinetic. However, the zero-order kinetic model was preferred because its fitting was higher. The values of kinetic constants were 0.081 (60°C), 0.185 (70°C), 0.270 (80°C) and 0.377 (90°C). According to the Arrhenius model, the activation energy for browning index in the range 60-90°C was 21.9kJ/mol.