Polyphenol oxidase (PPO) of garland chrysanthemum (Chrysanthemum coronarium L.) was purified approximately 32-fold with a recovery rate of 16% by ammonium sulfate fractionation, ion exchange chromatography, hydrophobic chromatography, and gel filtration. The purified enzyme appeared as a single band on PAGE and SDS-PAGE. The molecular weight of the enzyme was estimated to be about 47000 and 45000 by gel filtration and SDS-PAGE, respectively. The purified enzyme quickly oxidized chlorogenic acid and (-)-epicatechin. The K(m) value (Michaelis constant) of the enzyme was 2.0 mM for chlorogenic acid (pH 4.0, 30 degrees C) and 10.0 mM for (-)-epicatechin (pH 8.0, 40 degrees C). The optimum pH was 4.0 for chlorogenic acid oxidase (ChO) and 8.0 for (-)-epicatechin oxidase (EpO). In the pH range from 5 to 11, their activities were quite stable at 5 degrees C for 22 h. The optimum temperatures of ChO and EpO activities were 30 and 40 degrees C, respectively. Both activities were stable at up to 50 degrees C after heat treatment for 30 min. The purified enzyme was strongly inhibited by l-ascorbic acid and l-cysteine at 1 mM.

Soluble polyphenol oxidase of edible yam (Dioscorea opposita Thunb.) was purified approximately ,*--fold with a recovery rate of +/ῌ by ammonium sulfate fractionation, ion exchange chromatography, hydrophobic chromatography and gel filtration using dopamine as a substrate. The purified enzyme appeared as a single band on native PAGE and SDS-PAGE. The molecular weight of the enzyme was estimated to be approximately .,kDa and ..kDa using gel filtration and SDS-PAGE, respectively. The purified enzyme quickly oxidized dopamine. The apparent Km value (Michaelis constant) of the enzyme was +./ mM for dopamine (pH 1.*, -*ῌC). The optimum pH was 1.* for dopamine oxidase. In the pH range from 0 to +*, the activity was quite stable at /ῌC for ,, h. The optimum temperature of enzyme activity was ,/ῌ-*ῌC. The activity was stable up to /*ῌC after heat treatment for ,* min. The browning reaction by the enzyme was completely inhibited by + mM L-ascorbic acid, which reduced o-quinone to dopamine. The reaction was also completely inhibited by + mM L-cysteine, which is a known quinone coupler. About -/ῌ inhibition of edible yam PPO was observed using citric acid and acetic acid at +* mM in *.+ M citrate/ *., M sodium phosphate bu#er (pH 1). In consideration of the observed results, L-ascorbic acid, L-cysteine, acetic acid, and citric acid are expected to be used as e#ective inhibitors of enzymatic browning in edible yam.