Effects of ethephon and 1-methylcyclopropene on fruit ripening and the biosynthesis of volatiles in oriental sweet melon (Cucumis melo var. makuwa Makino)

Abstract

SummaryThe effects of 2-chloroethyl phosphonic acid (ethephon) and 1-methylcyclopropene (1-MCP) on the production of aroma volatile compounds, aroma-related enzyme activities, and the rate of respiration were investigated in two cultivars of oriental sweet melon [Cucumis melo var. makuwa Makino ‘Caihong 7’ (highly aromatic) and ‘Tianbao’ (less aromatic)] during storage at room temperature (approx. 23ºC). Ethylene production and the rates of respiration in fruit were enhanced by ethephon treatment, while decreased by 1-MCP. Ethephon advanced the onset of the climacteric peak of ethylene evolution and CO2 production in ‘Tianbao’ fruit. Moreover, emission of the characteristic aroma compounds identified in both cultivars were dependent on ethylene, showing an increase in response to ethephon treatment, and a strong reduction in response to 1-MCP treatment. Volatile esters predominated in both cultivars, among which acetic esters were the most abundant. Ethephon appeared to result in a preferential regulation of the levels of esters and alcohols in oriental sweet melon. Different levels of esters, alcohols, and aldehydes had a combined effect on the diversity of flavours in both cultivars. Lipoxygenase, alcohol dehydrogenase, and alcohol acyltransferase had a combined effect on the content and variety of aroma volatiles measured. The activities of these three enzymes showed positive regulation by ethylene.