Two Endogenous Substrates for Polyphenoloxidase in Pericarp Tissues of Postharvest Rambutan Fruit

• Published in: Journal of food science Vol. 75; no. 6; pp. C473 - C477
• Main Authors: Sun, Jian, Su, Weiqiang, Peng, Hongxiang, Zhu, Jianhua, Xu, Liangxiong, Bruñá, Nuria Martí
• Format: Journal Article
• Language: English
• Published: Malden, USA Blackwell Publishing Inc 01.08.2010; Wiley Subscription Services, Inc
• Subjects: Browning; Catalysis; Catalysts; Catalytic oxidation; Catechin - isolation & purification; Catechin - metabolism; catechol oxidase; Catechol Oxidase - isolation & purification; Catechol Oxidase - metabolism; Chemical compounds; Chemical Fractionation; Chemical reactions; Chromatography; Chromatography, High Pressure Liquid; Cold Temperature; contents; endogenous sources; endogenous substrates; enzymatic browning; enzyme substrates; enzymes; Ethyl acetate; Flavonoids - isolation & purification; Flavonoids - metabolism; food analysis; Food Handling; Food science; Foods; Fruit - chemistry; Fruit - enzymology; fruit composition; fruit quality; Fruits; Maillard Reaction; Nephelium lappaceum; Oxidation; pericarp; phenolic compounds; Phenols - isolation & purification; Phenols - metabolism; Plant Proteins - isolation & purification; Plant Proteins - metabolism; plant tissues; polyphenoloxidase; Polyphenols; Polyphenylene oxides; postharvest physiology; Proanthocyanidins - isolation & purification; Proanthocyanidins - metabolism; rambutan; rambutans; Sapindaceae - chemistry; Sapindaceae - enzymology; Storage; Substrate Specificity; Time Factors; Tissues
• ISSN: 0022-1147; 1750-3841
• DOI: 10.1111/j.1750-3841.2010.01660.x

The catalytic oxidation of phenolic substrates by polyphenoloxidase (PPO) causes pericarp browning of postharvest rambutan fruit. In the present study, PPO and its endogenous substrates were extracted from rambutan pericarp tissues (RPT). The substrate extracts were sequentially partitioned with ethyl acetate and n-butanol. The analysis of total phenolic content showed that the most phenolic compounds were distributed in ethyl acetate fraction. By high-performance liquid chromatography (HPLC), (-)-epicatechin (EC) and proanthocyanidin A2 (PA2) were identified from this fraction. After reacting with rambutan PPO, EC turned brown rapidly within 10 min, indicating that it was a significant endogenous substrate. Although PA2 could also be oxidized by the PPO, it turned brown very slowly. In addition, because EC and PA2 were continually catalyzed into browning products by PPO during storage of the fruit at 4 and 25 °C, their contents in RPT gradually declined with the extended storage time. It was further observed that both substrate contents in rambutan fruit storing at 25 °C decreased more rapidly than that storing at 4 °C, suggesting that low temperature inhibited the catalytic oxidation of substrates so as to slow down pericarp browning. Pericarp browning is a serious problem to storage and transport of harvested rambutan fruit. A generally accepted opinion on the browning mechanism is the oxidation of phenolic substrates by PPO. Ascertaining PPO substrates will effectively help us to control enzymatic reaction by chemical methods so as to delay or even prevent pericarp browning of harvested rambutan fruit.