Biochemical properties of oxidases of Yali pear
The biochemical properties of polyphenol oxidase (PPO), peroxidase (POD) and ascorbate peroxidase (APX) from Yali pear were investigated. The optimum pH and temperature of three enzymes was 5.6, 4.0, 7.0 and 20, 40, 50°C, respectively. Enzyme kinetics results showed that the Michaelis constant (Km) and maximum velocity (Vmax) of PPO for catechol were 0.22 M and 1111 U/ml/min. The Km and Vmax values of POD for guaiacol were 0.14 M and 1429 U/ml/min. The Km of APX for ascorbic acid and H2O2 were 0.41 and 0.083 mM, respectively, and the Vmax of APX was 455 and 208 U/ml/min for ascorbic acid and H2O2, respectively. The inhibitory effects of the four inhibitors (ascorbic acid, citric acid, L-cysteine and phytic acid) on each enzyme were different, suggesting that the composite inhibitor is more appropriate for processing of Yali pear.
Keywords: Yali pear, polyphenol oxidase, peroxidase, ascorbate peroxidase, biochemical property