Structures and Functions of Cuticular Wax in Postharvest Fruit and Its Regulation: A Comprehensive Review with Future Perspectives

Cuticular wax plays a major role in the growth and storage of plant fruits. The cuticular wax coating, which covers the outermost layer of a fruit’s epidermal cells, is insoluble in water. Cuticular wax is mainly composed of very long-chain fatty acids (VLCFAs); their derivatives, including esters, primary alcohols, secondary alcohols, aldehydes, and ketones; and triterpenoids. This complex mixture of lipids is probably biosynthesized in the epidermal cells of most plants and exuded onto the surface. Cuticular wax not only makes the fruit less susceptible to microbial infection but also reduces mechanical damage to the fruit, thereby maintaining the fruit’s commodity value. To date, research has mostly focused on the changes, function, and regulation of fruit wax before harvest, while ignoring the changes and functions of wax in fruit storage. This paper reviews on the composition, structure, and metabolic regulation of cuticular wax in fruits. It also focuses on postharvest factors affecting wax composition, such as storage temperature, relative humidity (RH), gas atmosphere, and as exogenous hormones; and the effects of wax on fruit postharvest quality, including water dispersion, fruit softening, physiological disorders, and disease resistance. These summaries may be of assistance in better understanding the changes in cuticular wax in postharvest fruit and the resulting effects on fruit quality.