Study on properties of polyphenol oxidase in dioscorea opposite and antibrowning without sulphite

Polyphenol oxidase activities of fresh Dioscorea opposite were spectrophotometrically determined at 408 nm with pyrocatechol as substrate at different pH,temperatures,substrate concentrations and inhibitors and so on.The results showed that the optimum pH and temperature for PPO activity was 6.0 and 30℃respectively,thermal stability of polyphenol oxidase was declined as the heating time increasing.Besides,polyphenol oxidase activity could be enhanced with raising substrate concentration and grew sharply with enzyme concentration increasing.Polyphenol oxidase activity could be restrained by four inhibitors (L-cysteine,citric acid,VC and NaCl) in varying degrees.The results of the orthogonal experiment showed that the optimal antibrowning without sulphite composition of Dioscorea Opposite was L-cysteine 0.02%,citric acid 1.4%,VC 0.016%,NaCl 2.5% and steeping time 3h.