Insight to Molecular Mechanism of Pericarp Browning in Litchi (Litchi chinensis Sonn.)

Abstract

Litchi (Litchi chinensis Sonn.) is a subtropical fruit crop having high commercial value and consumer acceptance due to its rich juicy aril and attractive bright red pericarp. Anthocyanin, the major pigment present in litchi pericarp reaches its maximum content in fully ripen fruit contributing to its bright red colour. The biosynthesis of anthocyanin occurs via an intricate phenyl propanoid pathway controlled by plethora of structural and regulatory genes. Several genes encoding enzymes responsible for anthocyanin synthesis have been isolated and characterised in different plants. Litchi fruit being highly perishable, exhibit relatively shorter postharvest shelf-life of 23 days at ambient conditions which in part can be attributed to the enzymatic and non-enzymatic degradation of anthocyanin. In contrast to the comprehensive understanding of molecular basis of anthocyanin synthesis, the studies on its catabolism or degradation are meagre. Polyphenols oxidases and peroxidases are the major enzymes responsible for anthocyanin degradation leading to the problem of pericarp browning. Laccase, an anthocyanin degradation enzyme expresses about thousand fold higher than the polyphenols oxidase in the pericarp with epicatechin as favourable substrate. A detailed study of the anthocyanin degradation pathway in litchi may be helpful in managing the problem of pericarp browning to preserve its bright red colour as well as to enhance the shelf life and marketability of this valuable fruit crop.