Characterization of polyphenol oxidase from Uapaca kirkiana fruit

• Published in: Journal of the science of food and agriculture Vol. 86; no. 2; pp. 328 - 332
• Main Authors: Muchuweti, M, Mupure, C.H, Ndhlala, A.R, Kasiyamhuru, A
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 30.01.2006; Wiley; John Wiley and Sons, Limited
• Subjects: Biological and medical sciences; catechol oxidase; enzyme activity; enzyme inhibition; enzyme inhibitors; Enzymes; Euphorbiaceae; Food industries; Food preservation; Food science; Fruit and vegetable industries; fruit crops; fruit pulp; fruit quality; Fruits; Fundamental and applied biological sciences. Psychology; isoenzymes; isozymes; molecular weight; peels; polyphenol oxidase; postharvest; Temperature; tropical and subtropical fruits; Uapaca kirkiana; Characterization; Fruit; fruits; isoenzymes; Enzyme; Isozyme; Uapaca kirkiana; Postharvest; Catechol oxidase; polyphenol oxidase; Oxidoreductases
• ISSN: 0022-5142; 1097-0010
• DOI: 10.1002/jsfa.2329

Polyphenol oxidase (PPO), the enzyme responsible for the postharvest spoilage of fruits, was extracted and purified from Uapaca kirkiana peel and pulp by ammonium sulfate precipitation and dialysis. Further purification of peel PPO was carried out by gel filtration chromatography. Optimum pH values were 7 and 8 for peel and pulp PPO, respectively. The optimum temperatures for peel and pulp PPO were 45 and 35 °C, respectively. Inhibition studies of the PPO enzyme were performed using citric acid, sodium azide, sodium metabisulfite and thiourea. The most effective inhibitors were sodium azide and citric acid for both peel and pulp PPO. Vmax and Km values were 13.63 units min-1 and 4.923 mmol L-1, respectively, for peel PPO and 14.03 units min-1 and 5.43 mmol L-1, respectively, for pulp PPO. Three isoenzymes of Uapaca kirkiana PPO were detected by polyacrylamide gel electrophoresis. One of the isoenzymes could be identified as having a molecular weight of 26 625 Da.