Abstract
ABSTRACT A comparative study of polyphenol oxidase (PPO) from two Turkish varieties of quince (Eşme and Kalecik) was conducted to determine some of the characteristics of the enzymes in terms of temperature and pH optima, substrate specificity, thermal inactivation and potency of some PPO inhibitors. PPO was partially purified by ammonium sulfate precipitation followed by dialysis. The optimum pH and temperature of the two PPOs were found to be similar. The apparent substrate specificity was established from Vmax/Km as 4-methylcatechol > catechol > pyrogallol for PPO from Eşme variety (PPOEşme). The substrate specificity for PPO from Kalecik variety (PPOKalecik) was catechol > 4-methylcatechol > pyrogallol. Heat stabilities and substrate specificities of the two enzymes differed. PRACTICAL APPLICATION Turkey is the main quince producer in the world. There are many quince types and cultivars grown in different parts of Turkey. It is consumed as fresh fruit, as well as processed into different products. As with many fruits and vegetables, enzymatic browning catalyzed by polyphenol oxidase (PPO) (EC 1.14.18.1) also occurs in quince. A successful prevention of these reactions requires characterization of PPO. The biochemical properties of PPOs determined in this study are important for controlling enzymatic browning which occurs during handling and processing of quince fruits.
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