Role of anthocyanins, polyphenol oxidase and phenols in lychee pericarp browning

Postharvest browning of lychee fruits is investigated in relation to anthocyanins, polyphenol oxidase (PPO) and phenols, using a purified PPO, anthocyanin extract and phenolic extract. Lychee PPO cannot oxidise the degradation of anthocyanins, but the presence of phenolic extract stimulates pigment degradation by PPO, leading to the development of brown pigments. The absorbance at 410 nm of the reaction solution is correlated well with the peel browning index. Pyrogallol, catechol and 4-methylcatechol are good stimulators, but no action with chlorogenic acid, p-cresol, resorcinol or tyrosine is observed. A decrease in the ascorbic acid content of lychee pericarp is associated with an increase in the peel browning index, and the addition of ascorbic acid to the reaction mixture exerts a preventive action on the anthocyanin degradation. Data here suggest that anthocyanins, PPO and phenols contribute to lychee pericarp browning involved in anthocyanin–PPO–phenol reactions.