Proanthocyanidin delays litchi peel browning by inhibiting ethylene biosynthesis, respiratory metabolism, and phenol oxidase activities

Proanthocyanidin (PA) promotes antioxidant capacity and enhances resistance against oxidative stress-induced senescence in fruits after harvest. However, the effects of PA on the postharvest physiology of litchi fruit remain unclear. This study aimed to determine the effect of PA on ethylene and respiration physiology, and on browning enzymes of ‘feizixiao’ litchi stored at 25 °C for 8 d. Proanthocyanidin treatment delayed peel browning and color change, maintained higher peel lightness, and reduced ethylene production and respiration rates in litchi fruit. Subsequently, the key genes and/or enzymes involved in the ethylene biosynthesis pathway and respiration metabolism were determined. The PA-treated fruit exhibited lower levels of 1-aminocyclopropanecarboxylic acid (ACC) content, ACC synthase (ACS) and ACC oxidase (ACO) activity, and an inhibition of LcACS7/9 and LcACO1/2 genes on the peel and pulp compared to that of the control. In addition, the application of PA reduced respiration rate by downregulating the expression of LcAtpB, LcAOX1, LcUCP1, LcAAC1, and LcSnRK2. Furthermore, the phenol oxidase including peroxidase (POD), polyphenol oxidase (PPO), and laccase (LAC), were inhibited during litchi peel browning and senescence. Therefore, the process of PA-delayed browning of litchi may occur by delaying ethylene production and respiratory rate and inhibiting phenol oxidase activities in litchi fruit.