Combined physiological, biochemical, and multi-omic analyses provide insight into the cause of differential browning in early and late harvested fresh-cut yams

Tissue browning reduces the cosmetic quality of fresh-cut yams and poses a marketing problem. The degree of browning of fresh-cut yams varies depending on when they are harvested. In this study, transcriptomic and metabolomic analyses were conducted in yams harvested in September (DHPS) and October (DHPO) to determine the mechanisms responsible for the browning of fresh-cut yams. Results showed that the browning index, total phenol and lignin content, polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia-lyase (PAL), 4-coumarate: CoA Ligase(4CL), and cinnamic acid-4-hydroxylase(C4H) activity in fresh-cut DHPO yams were lower than they were in fresh-cut DHPS yams. Flavonoids and catalase (CAT) activity remained consistently higher during storage in DHPO yams than in DHPS yams. The browning of fresh-cut DHPO yams was mitigated by the regulation of the expression of genes and the abundance of metabolites associated with phenolic metabolism, phytohormones, and signal transduction, as well as sucrose and starch metabolism. The level of browning enzyme activity in DHPO yams was significantly lower than it was in DHPS yams. Our study provides a basis for the selection of optimum harvest date for yams that will undergo fresh-cut processing.