Alcohol Acetyltransferase Activity, Ethylene Production and Aroma Formation of Muskmelon during Fruit Development

Muskmelon (Cucumis melo L.) varieties differ in a range of physical and chemical attributes. Aroma is one of the most important factors determining fruit quality and consumer preference. Volatile esters, a major class of compounds contributing to the aroma of muskmelon fruit, are synthesized by alcohol acyl-transferases (AATs). We demonstrate here that volatile aldehydes are most abundant in unripe ‘Shannong Golden1’ fruit, a climacteric muskmelon but volatile esters are the major components of ripe fruit. In contrast, both ripe and unripe ‘Sweet Delight’ fruit, a non-climacteric muskmelon, had an abundance of volatile aldehydes. Unripe ‘Takami’ fruit, another climacteric muskmelon, had an abundance of alcohols and aldehydes whereas ripe fruit of this cultivar had an abundance of esters and aldehydes. Ripe ‘Takami’ fruit produced ethylene at an intermediate concentration relative to that of ‘Shannong Golden1’ and ‘Sweet Delight’. Interestingly, the levels of AAT of all three cultivars mirrored ethylene concentrations and again were highest in ripe ‘Shannong Golden1’ fruit and lowest in ‘Sweet Delight’ fruit. These data suggest that the volatiles differ between fruit types and higher ethylene concentrations result in higher volatile ester concentrations in muskmelon. Furthermore, AAT activity appears to be positively correlated with volatile esters produced during muskmelon ripening and thus may play an important role in aroma formation. _____________________________________________________________________________________________________________