Variations in contents of browning substrates and activities of some related enzymes during litchi fruit development

Pericarp browning is a major factor to limit storage and transportation of postharvest litchi fruit. Experiments were conducted firstly to determine variations in contents of browning substrate (-)epicatechin in pericarp tissues Of litchi fruit during development. Changes in the activities of polyphenoloxidase (PPO), peroxidase (POD) and phenylalanine ammonialyase (PAL) in association with the synthesis or oxidation of (-)-epicatechin were also examined. (-)-Epicatechin content tended to decrease during fruit development. PAL activity had a high level at the initial stage of fruit development, then decreased rapidly, and Finally increased slightly, which was in agreement with the variation in (-)epicatechin content. The higher contents of total phenolics and (-)-epicatechin of fruit of 'Nuomici' than 'Feizixiao' were also related to the higher PAL activity. PPO had a similar change to PAL in activity, but POD activity slowly decreased at the early fruit development and then increased markedly. It is suggested that (-)-epicatechin content might be largely regulated by PAL activity. This study Could help to understand the variations in the content of the browning substrate and the activities of some substrate-related enzymes of litchi fruit during development and then control better pericarp browning of harvested litchi fruit by the application of appropriate preharvest treatments. (c) 2008 Elsevier B.V. All rights reserved.