Partial Purification and Characterization of Polyphenol Oxidase from Water Yam ( Dioscorea alata )
Ojimelukwe, P. C.
Bede, E. N.
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The aim of this research was to evaluate enzymic browning of Discorea alata and determine methods of preventing and controlling the browning reaction. Polyphenol oxidase (PPO) was extracted from water yam and partially purified by acetone precipitation and dialysis. Optimal pH activity, substrate specificity and inhibition studies of this enzyme was carried out. The result revealed a 9.9 fold increase in activity after dialysis of acetone enzyme precipitate. Substrate specificity of water yam PPO showed activity for diphenolic compounds- catechol, methylcatechol and L-DOPA while no activity was observed in the presence of monophenolic compound, p-cresol. Optimal pH activity of this enzyme was observed at pH 6.8. Tyrosine, phenylthiourea and hydroquinone inhibited water yam PPO competitively in the presence of catechol while ascorbic acid and 2-mercaptoethanol completely inhibited this enzyme at concentrations used. Activation of catechol oxidation by the water yam PPO was observed in the presence of pyrogallol and garlic acid. The data obtained from this inhibition study may be used to predict prevention of browning in yam tuber using chemical inhibitors.