Characterization of polyphenol oxidase extracted from Thompson seedless grape

【Objective】 Polyphenol oxidase(PPO) was extracted from Thompson seedless,and its characteristics were studied to provide information for raisins processing.【Method】 Characteristics,including optimal temperature and pH for enzymatic reaction,and influences of enzyme dose and substrate concentration on the enzymatic activity were studied.Michaelis-Menten constant(Km) and maximum velocitiy of the reaction(Vmax)were also calculated on the basis of obtained kinetic functions for the enzymatic reaction when catechol was used as the substrate.【Result】 The results showed the optimal condition for the PPO was pH 6.0 and 25 ℃,with Km and Vmax values of 45 mmol/L and 500 U/min,respectively,when catechol was used as the substrate.The enzyme showed high stability for 60 min at temperatures lower than 25 ℃,its activity was partially daraged at 30-60 ℃ and could be inhibited completely at temperatures higher than 70 ℃ within 10 min.【Conclusion】 High temperature and short time treatment can reduce enzymatic activity and it can be extended,as a method of pre-treatment in raisins processing.