Heat sensitivity of different mustard ( Sinapis alba L.) genotype myrosinase enzyme

Mustard seed ( Sinapis alba L.) has valuable chemical composition and its cultivation in moderate climate, especially in Hungary is economically feasible. In spite of the advantageous chemical composition and colloid-chemical properties, the use of mustard seed flour is limited in food industry or in animal feeding because of its pungent taste. The pungent taste develops through the action of myrosinase; but it could be eliminated by heat inactivation of the enzyme. In the course of our preliminary experiments, it was observed that heat inactivation of the myrosinase enzyme depended on mustard variety. The heat stability of myrosinase enzyme prepared from different mustard varieties was examined and compared in our research work. Crude myrosinase was prepared from three mustard genotypes (Budakalászi, Tilney, and LM-1 (a low erucic acid content cultivar) and the heat stability was determined at 60, 70 or 80 °C for 5, 10, 15, 20 and 30 min. The semi-logarithmic plots of myrosinase activity as a function of time at different temperatures indicated that heat inactivation of crude myrosinase enzyme follows first-order kinetics. Characterising the rate of inactivation by the slope of the curve, significant differences were established in heat stability between genotypes at 60 °C. There were no significant differences between varieties at higher temperatures (70 and 80 °C). Longer than 10 min heat treatment causes more than 90% inactivation of the enzyme