Physiological, biochemical and anatomical changes in lychee (Litchi chinensis Sonn.) pericarp during storage

Polyphenol oxidase activity, anthocyanin concentration, endogenous ethylene production and anatomical features of mature lychee (Litchi chinensis Sonn.) pericarp were studied to understand better post-harvest tissue browning. Polyphenol oxidase (PPO) activity decreased significantly once fruit were harvested. Although anthocyanin degradation occurred, it was far slower than tissue browning. It is considered unlikely that pericarp browning is due to direct pigment degradation by polyphenol oxidase. Pericarp browning may in fact be caused by non-PPO mediated anthocyanin decolorization, coupled with localized PPO activity affecting secondary metabolites other than anthocyanin. Pericarp browning was correlated with moisture loss. The development of pericarp micro-cracking after harvest was observed, and may be involved in facilitating rapid pericarp moisture loss.