Isolation of a Latent Polyphenol Oxidase from Edible Yam (Dioscorea cayenensis-rotundata cv. Zrèzrou) Cultivated in Côte D’ivoire

A polyphenol oxidase was purified to homogeneity from edible yam (Dioscorea cayenensis-rotundata cv. zrèzrou) cultivated in Côte d’Ivoire. The purification procedure consisted of ion-exchange, ammonium sulphate fractionation, size exclusion and hydrophobic interaction chromatography. Dopamine was used as substrate. The enzyme designated PPOZ had native molecular weight of approximately 64.56±0.03 and 64.08±0.23 kDa and functioned as monomer structure. Maximal PPOZ activity occurred at 30°C and pH 6.0. The enzyme was stable at 30°C and its pH stability was in the range of 5.6–7.0. Substrate specificity revealed that the purified enzyme oxidized preferentially dopamine and then, catechol and catechin. PPOZ showed no activity toward the monophenols and was completely inhibited by beta-mercaptoethanol, sodium thiosulphate, L-ascorbic acid, sodium bisulphite and L-cysteine reagents and it was strongly activated by SDS. In this study; the latent PPO was kinetically characterized in parallel with an active PPO present in the soluble fraction.