Activation of Ester Production in Japanese Apricot Fruit Stored under High-oxygen Atmosphere

Various postharvest techniques have been developed to preserve freshness and avoid deterioration of fresh products such as fruits and vegetables by suppressing their metabolic changes toward senescence. We have been focusing on using post-harvest metabolic changes in fruits as a means of material processing to achieve novel characters rather than just delaying senescence. Japanese apricot (Prunus mume) fruit is a popular material for liqueur in Japan. Usually mature green fruits are used for the liqueur. To produce aroma-rich Japanese apricot fruits, we have been investigating the post-harvest treatment on these fruits to increase their content of aromatic compounds such as volatile esters, including hexyl acetate or butyl acetate. Volatile ester biosynthesis was initiated earlier under high-oxygen atmosphere (upto 80 %) than under normal atmosphere, and the amount of esters also increased. These changes depended on ambient oxygen concentration. The composition of esters in fruits was also affected by storage period; hexanol and butanol esters increased during a storage period of less than 5 days and ethanol esters tended to increase after a storage period of more than 6 days. Alcohol acyltransferase (AAT) activity catalyzing ester biosynthesis and the lipoxygenase–hydroperoxide lyase (LOX–HPL) pathway for the synthesis of short-chain fatty-acids and alcohols as precursors of esters were found to vary in a coordinate way with ester synthesis under high-oxygen atmosphere. It is considered that the increase in esters was caused by a combination of metabolic changes: 1) The LOX–HPL pathway is activated just after storage under high-oxygen atmosphere, 2) AAT activity is increased earlier under high-oxygen atmosphere than under normal atmosphere. The high-oxygen treatment developed in this study has made it possible to engineer fruit metabolism, and further produce fruits having increased amounts and modified composition of esters.