Litchi postharvest physiology and handling

Abstract

Litchi (Litchi chinensis Sonn.) fruit, with its bright red color and sweet and juicy aril, is an important fruit crop in Asia, Africa, Australia, and South America. A major cause of the postharvest loss of litchi fruit is browning and decay. Chlorophyll breakdown and flavonoid synthesis occur simultaneously during the maturation of this nonclimacteric fruit. However, once litchi fruit is harvested, pericarp desiccation and membrane breakdown occur, which leads to browning with the rate of browning and later microcracking paralleling water loss rate. In addition, chilling injury can contribute to and increase pericarp browning and membrane leakage. Polyphenol oxidase and peroxidase are possibly key enzymes in the early stages of browning. An increase in the leakage of the pericarp membrane also occurs that correlates with browning. Many chemical treatments have been evaluated to retard pericarp browning, such as melatonin, hot water, acidified calcium sulfate (ACS), adenosine triphosphate, and tea seed oil. During long distance transportation, chemical treatments that involve sulfur are used, including SO2 fumigation, acid dip after SO2 fumigation, SO2 fumigation and sulfur sheet package, or SO2 fumigation followed by controlled atmosphere (CA), if approved by the importing country. Other treatments that avoid the use of SO2 include melatonin, ACS, and hot water brushing combined with an acid dip, CA, and modified atmosphere packaging. Anthracnose is a common disease that accelerates browning and decay. Penicillium species as a saprophyte is also common with fruit infection occurring in the field, during harvest, in the packhouse, cold rooms, and shipping containers. Sulfur sheet or CA is used to reduce fruit rot after SO2 fumigation and Sportak (prochloraz) for the control of penicillium. However, a replacement for postharvest SO2 use is still urgently needed.