Volatile Precursors and Aroma-Related Enzyme Activities during Fruit Maturation of Muskmelon

Fatty acids and amino acids serve as ester precursors, in addition to lipoxyaenase (LOX; EC 1.13.11.12), alcohol dehydrogenase (ADH; EC 1.1.1.1) and alcohol o-acyltransferase (AAT; EC 2.3.1.84) activities, were assessed during maturation of climacteric and nonclimacteric muskmelons. The results showed that the levels of the main fatty acids related to aroma formation containing oleic acid, linoleic acid and linolenic acid during fruit development of ‘Shannong Golden 1’, a climacteric muskmelon were much higher than those in fruits of ‘Sweet Delight’, a non-climacteric muskmelon. The amino acids contents were very high in 15 days after pollination (DAP) fruit of ‘Shannong Golden 1’, but dramatically decreased in 30 DAP fruit and reached the lowest levels in mature fruit. But, these amino acids levels almost had no changes during fruit development of ‘Sweet Delight’. In contrast to amino acids levels, ADH and LOX activities showed almost the same change trends, however, AAT activities were significantly different during fruit development of these two cultivars. Together, our data suggested that AAT activity, fatty acids and amino acids contents may play important roles and LOX and ADH may be not the limiting factors in ester volatiles production in muskmelon fruit. _____________________________________________________________________________________________________________