Abstract
Enzymatic browning reactions by polyphenol oxidases cause alteration of appearance, flavor and nutritive value of vegetables and fruits. It is one of the important problems for vegetables used as salads and causes lots of economic losses. In this study, polyphenol oxidase (PPO) from Eruca sativa was extracted and characterization studies were carried out. Substrate specificity for variable substrates, optimum pH, optimum temperature, effect of different metal ions were assayed. Km and Vmax values were determined as for pyrocatechol Km = 10.24 mM, Vmax = 0.0018 U min-1, catechin; Km = 12.57 mM, Vmax = 0.0012 U min-1, gallic acid; Km = 23.07 mM, Vmax = 0.0001 U min-1. Optimum pH and temperature were determined as pH:7.0 and 20 oC respectively. Effect of various metal ions such as, K+, Fe2+, Mg2+, Zn2+, Cu2+ and Hg2+ on enzyme activity were measured. K+, Mg2+, Zn2+, Cu2+ ions inhibited PPO activity significantly. However Fe2+ ion did not inhibit PPO activity.
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