Effects of intermittent warming on aroma-related esters of 1-methylcyclopropene-treated ‘Nanguo’ pears during ripening at room temperature

Abstract

Refrigeration combined with 1-methylcyclopropene (1-MCP) treatment is an effective method for the long-term storage of climacteric fruit, but this benefit is offset by a loss of aroma when the fruit is then ripened at room temperature. The pear cv. ‘Nanguo’ (Pyrus ussuriensis Maxim.) was treated with 1-MCP and continuously stored at 0±0.5°C or exposed to the same storage temperature alternated with 20±1°C for 1 d every 20 d during storage (namely, intermittent warming [IW]). Changes in aroma-related esters, levels of fatty acids, and the activity and gene expression of alcohol acyltransferase (AAT) and lipoxygenase (LOX) were investigated. Changes in the gene expression of the enzymes (1-aminocyclopropane-carboxylase (ACC) synthase (ACS) and ACC oxidase (ACO)) involved in ethylene biosynthesis and the expression of genes involved in ethylene signal transduction were also studied. Significantly higher ester content was found in IW-treated fruit. Increased activity and gene expression of AAT, LOX, and accumulated polyunsaturated fatty acids were associated with enhanced aroma quality in IW-treated fruit. The increased translation levels of PuACS1 and PuACO1 contributed to the elevated ethylene levels in IW-treated fruit. IW treatment seemed to have no significant effect on the induction of the expression of PuETR1 and merely stimulated the expression of PuCTR1 during the prior period of the shelf life at 20°C. Treatment with IW effectively prevented the loss of aroma-related esters from 1-MCP-treated ‘Nanguo’ pears, and possible mechanisms for this were discussed.