Comparative study of the biochemical properties of membrane-bound and soluble polyphenol oxidase from Prunus mume

Abstract

Browning occurs during fruit and vegetable processing mainly as a result of oxidation by polyphenol oxidases. We compared the biochemical properties of membrane-bound polyphenol oxidase (mPPO) and soluble polyphenol oxidase (sPPO) isolated and purified from Prunus mume. The sPPO showed a greater affinity for the substrate catechol. The highest activity of sPPO was catechol, while those of the mPPO were catechol and 4-methylcatechol. The optimum pH of sPPO was 5.0, while that of the mPPO were 4.5 and 5.5; the optimum temperatures of sPPO and mPPO were 40 °C and 60 °C, respectively; and the sPPO was more resistant to acidic environments, while the mPPO maintained better stability within temperature changes. The metal ions Mg2+ and Na+ were able to activate both sPPO and mPPO of P. mume, while Al3+ and K+ significantly inhibited their activities, and both Cu2+ and Ca2+ inhibited the activity of sPPO but activated that of mPPO. Different inhibitors were found to have different effects on sPPO and mPPO, however, sodium sulfite, sodium bisulfite, l-cysteine, glutathione and ascorbic acid had obvious inhibitory effects on both forms of polyphenol oxidase. Provide theoretical support for the research on the characteristics and browning mechanism of polyphenol oxidase in fruits and vegetables.