Phenolic components, antioxidant enzyme activities and anatomic structure of longan fruit pericarp following treatment with adenylate triphosphate

Abstract

Fruit senescence and pericarp browning are strongly related to the antioxidant properties and are affected by the cellular energy status. In the present study, longan fruits were treated with 1mmolL−1 adenosine triphosphate (ATP) before storage for six days at 25°C. The phenolic contents and antioxidant enzyme activities in relation to pericarp browning were determined, and the fruit pericarp structure was observed under a confocal laser scanning microscope (CLSM) and transmission electron microscope. Increases in the browning index, membrane permeability, peroxidase (POD) activity and gallic acid content were slowed during storage following exogenous ATP application, whereas the flavonoids accumulation was increased significantly by ATP treatment. In addition, decrease in catechin, corilagin, epicatechin and gallocatechin gallate were accelerated by exogenous ATP treatment. The cuticle in the pericarp of the untreated longan fruit was incomplete, the organelle was swollen or disintegrated, the grana lamellae was destroyed and osmiophilic particles accumulated in the chloroplast, the cytoplasm was granulated and the fruiting body of a possible pathogenic organism was observed after storage. However, the pericarp structure maintained its relative integrity without any visible pathogenic organisms, as determined with CLSM in the ATP-treated fruit. It is suggested that ATP application protects longan fruit from pathogen attack, maintains the pericarp structure and delays senescence, which are closely related to the fruit's higher total phenolic levels and lower POD activity.