Effect Of Preharvest ASA Treatments On Main Aroma Compounds Metabolism And Postharvest Quality Of Muskmelon Fruit

Muskmelon(Cucumis melo L.) is a climacteric fruit, postharvest metabolism is active and shelf life is short. Acetylsalicylic acid(ASA) is a derivative of salicylic acid(SA) capable of maintain fruit postharvest quality. However, little information is available about the effects of ASA on ethylene biosynthesis and aroma metabolism of muskmelon fruits. Muskmelon(cv. Manao) fruits were sprayed with ASA at 1.0 m M for four times before harvest. The influence of preharvest ASA treatments on ethylene biosynthesis, key enzymes and genes based on LOX pathway involved in aroma biosynthesis, volatiles release and postharvest quality were investigated. The results indicated as follows:1. ASA treatments significantly inhibited ethylene production, retarded ethylene peak and suppressed the expression of Cm ACS and Cm ACO during storage. Therefore, ASA could exert an influence on ethylene biosynthesis and make ethylene production lower than the control fruits.2. ASA treatments significantly suppressed the activity of LOX, HPL, AAT and the expression of corresponding genes before the ethylene climacteric. While the ADH activity and the expression of its gene were improved in ASA-treated fruits, which was possibly not regulated by ethylene. After the ethylene climacteric,.ASA treatments enhanced the activity of HPL and AAT and the transcriptional level of its gene.3. As a result of the increase in the levels of aldehydes and alcohols, ASA treatments increased total volatiles content at harvest, while suppressed the release of esters. After the ethylene climacteric, the contents of aldehydes, alcohols and esters enhanced in ASA-treated fruits in late storage, especially esters, which was possibly caused by the influence of straight-chain aldehydes, alcohols and esters derived from LOX pathway. And the variation trend of these straight-chain compounds was similar to that of total aldehydes, alcohols and esters.4. The possible characteristic aroma compounds of ‘Manao’ fruits were as follows: including Butanoic acid, 2-methyl-,ethyl ester, 2-Nonenal,(E)-,6-Nonenal,(Z)-,trans-á-Ionone, 2,6-Nonadienal,(E,Z)-,Butanoic acid, ethyl ester, 3-Nonen-1-ol,(Z)-,Hexanoic acid, ethyl ester, 1-Octen-3-ol, Butanoic acid, 2-methyl-,methyl ester, Acetic acid, hexyl ester, Nonanal, 1-Butanol, 2-methyl-, acetate, Benzyl acetate. These compounds made positive contributions to characteristic aroma of muskmelon fruits. And ASA treatments significantly increased the release of these compounds in late storage.5. ASA treatments effectively inhibited the rise of weight loss and the decline of fruit firmness, and retarded the rate of peel to yellow, as well as maintained total soluble solids(TSS) and titratable acid(TA) contents. Therefore, ASA treatments kept the postharvest quality and delayed the senescence process of muskmelon fruits.In conclusion, preharvest ASA treatments regulated key enzymes activity and the expression of corresponding genes involved in LOX pathway, enhanced the levels of aldehydes, alcohols and esters in late storage. And ethylene had an influence on esters biosynthesis by regulating AAT activity. In addition, ASA treatments maintained the postharvest quality of muskmelons by means of inhibitting ethylene metabolism.