Purification and Characterization of Polyphenol Oxidase from Edible Yam (Dioscorea opposita Thunb.)

Abstract

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.

Some characteristics of polyphenol oxidase purified from edible yam (Dioscorea cayenensis‐rotundata cv. Longbô) cultivated in Côte d’Ivoire

“…The purified enzyme was very similar to PPO from edible yam (Dioscorea opposita Thunb.) (Fujita et al, 2006) and to the banana (Musa sapientum) pulp PPO (Yang et al, 2000), but different to the PPO from white yam (D. rotundata), which quickly oxidised chlorogenic acid and catechol (Ikediobi & Obasuyi, 1982). The different substrate specificity between Dioscorea cayenensis-rotundata cv.…”

“…Guiwei) fruit (Sun et al, 2008) and another species of yam tuber (Anosike & Ayaebene, 1981;Ikediobi & Obasuyi, 1982). However, it differed from PPOs of Barbados cherry (Malpighia glabra) (Kumar & Mohan, 2008) and edible yam (Dioscorea opposita) (Fujita et al, 2006). The pH stability profile for the enzyme showed that 100% of the PPO Y activity was retained between pH 6.0 and 7.0.…”

“…The pH stability profile for the enzyme showed that 100% of the PPO Y activity was retained between pH 6.0 and 7.0. The PPO system in yams was shown to be most active at a near neutral pH value (Fujita et al. , 2006).…”

“…The pH stability profile for the enzyme showed that 100% of the PPO Y activity was retained between pH 6.0 and 7.0. The PPO system in yams was shown to be most active at a near neutral pH value (Fujita et al, 2006). According to Lee et al (1990), the rapid inactivation of the enzyme above pH 8.0 may be due to conformational changes in the enzyme under the alkaline conditions and ⁄ or the enzyme may react rapidly with quinones through Maillard reactions and ⁄ or Strecker degradation.…”

Removal of bisphenol derivatives through quinone oxidation by polyphenol oxidase and subsequent quinone adsorption on chitosan in the heterogeneous system

“…[38,40,41] Figure 2 shows the effect of the pH value on PPO-catalysed quinone oxidation of the bisphenol derivatives at 40°C. The conversion % value at the reaction time of 5 h was used as the evaluation index for BPB, BPC, and BPZ.…”