Effects of Grafting on Main Esters, Free Amino Acids Content and Related Enzyme Activities in Oriental Sweet Melon Peel and Flesh Tissues

Objective The objective of this experiment is to define the primary mechanism of grafting on aroma volatiles in oriental sweet melon and elucidate the relationship between amino acids and volatile esters. The effects of grafting on main volatile esters, amino acids and related enzymes activities at different development periods in oriental sweet melon peel and flesh tissues were studied. Method Four main esters(i.e. ethyl acetate, 1-butanol, 2-methyl acetate, hexyl acetate, and phenylmethyl acetate) were collected using the solid-phase microextraction (SPME) and then quantified by GC. Also, free amino acids composition and content were investigated, and the key enzymes activities, which involved in esters biosynthesis were measured as well. Result Grafting increased ethyl acetate content in peel and flesh tissues and decreased hexyl acetate and phenylmethyl acetate content. 2-methyl-1-butyl acetate content in peel tissue increased, while that declined in flesh tissue in grafted melons. Sixteen kinds of free amino acids were detected in peel and flesh tissues of melon. Amino acids content gradually increased with fruits development, and the content in grafted melons was higher than own-rooted fruits at early stages; however, which lower than own-rooted fruits at middle and later stages. The biosynthesis relationship between valine, leucine and isoleucine and 2-methyl-1-butyl acetate were validated. The enzymes activities in peel (P0.01) and flesh tissue (P0.05) of ADH and AAT significantly decreased in grafted melons. Conclusion Grafting altered the main esters contents in oriental sweet melon peel and flesh tissues. In addition, the esters contents in peel tissue were higher than in flesh at maturity. It decreased most of free amino acids content, and parts of amino acids were involved in the biosynthesis of branched-chain esters. The enzymes activities of ADH and AAT were lower in grafted melons than own-rooted ones.