Study On The Difference Of Aroma Components Of Different Varieties Of Oriental Melon(Cucumis Melo Var.makuwa Makino)

Oriental melon(Cucumis melo var.makuwa Makino),commonly known as "aroma melon",is popular with the public because of its rich aroma,sweetness and juicy.Aroma is one of the important quality characteristics of oriental melon,which directly affects consumers’ choices.The aroma characteristics of oriental melon are extremely complex,and different varieties of fruits have different aroma types due to the different composition of aroma substances.Therefore,it is of great significance to clarify the specific reasons for the differences in the composition and content of aroma substances in fruits to regulate the flavor quality of oriental melo n.In this study,the fruits of four different varieties of oriental melo n ’YMR’,’HPM’,’B9’and ’XSM’ at different ripe stages(green fruit stage,color conversion stage,and ripe stage)were used as test materials to determine the melon The physiological and biochemical indicators of fruits,the types and contents of aroma substances,the key enzyme activities in aroma synthesis pathways and the changes in their gene expression provide a basis for exploring the mechanism of differences in aroma substances in melon fruits.The main findings are as follows:1.To determine the ripening characteristics of different melon varieties by measuring the fruit soluble solid(SSC),hardness,ethylene release rate and other indexes.The electronic nose technique was used to detect the flavor of melon fruits of different varieties and different periods.The results showed that there were obvious differences in aroma components of four kinds of melon in different periods.2.Gas chromatography-mass spectrometry(GC-MS)analysis was performed on the fruits of oriental melon at different ripe stages.The results showed that a total of 57 aroma substances were detected,including 25 esters.The content of total aromatic substances "XSM" in ripe fruits was the lowest,and the fruit fragrance was the least.The content of "YMR" and "HPM"aroma substances was about 3 times of "XSM",with strong aroma.The content of total aromatic substances of "B9" was between "YMR","HPM" and "XSM",which was about twice that of "XSM",and its aroma was middle-aromatic(stronger fragrance).Ethyl acetate,benzyl acetate,2-methyl-butyl acetate,hexyl acetate,stearic acid,palmitic acid,(E,E)-2,4-nonadienal,2-n-pentylfuran were the key substances that caused the difference in the aroma of four varieties of melon.According to the odor activity value,it could be seen that the contribution of aroma substances to the fruit was ’YMR’>’HPM’>’B9’>’XSM’.The contrib ution of aroma substances with different odors to melon fruits of different varieties was different.Therefore,melon fruits were classified according to the description of aroma substances.’YMR’ was floral and fruity.’HPM’ was fruity,’XSM’ showed green,and ’B9’was a variety with a stronger scent,belonging to an intermediate scent.3.The activities of lipoxygenase(LOX),alcohol dehydrogenase(ADH)and alcohol acyl transferase(AAT)were different among different melon fruits.The activities of three enzymes increased gradually with fruit ripening.In ripe fruits,the activities of LOX,ADH and AAT of’YMR’ were the highest,and AAT changed the most with ripening,which was about 5～6 times that of green fruit stage(S1).The expression level of CmLOX12 was the highest in’XSM’ with green.The expression level of CmLOX01 was the highest in the ripe fruit of ’B9’with stronger aroma.It was suggested that they may play a certain role in the formation of characteristic aroma.CmLOX09,CmADH12,CmAATl and CmAAT2 expressed significantly differently in different fruits,which may be involved in the formation of aroma differences of different fruit varieties.The expression levels were high in ripe fruits with strong aroma,and the variation trend of expression levels was similar to that of enzyme activities.The expression levels of CmAATl and CmAAT2 were much higher than those of other genes,which were highly correlated with the aroma level of ripe fruits with high ester content.In summary,’YMR’ and ’HPM’ were strong in aroma,among which ’YMR’ were floral and fruity,and ’HPM’ were fruity.’XSM’ were light,and belonged to green.’B9’ had stronger aroma and belonged to middle aroma.Lipoxygenase(LOX),alcohol dehydrogenase(ADH)and alcohol acyltransferase(AAT)were involved in the synthesis of melon aroma to varying degrees.And it was initially clear that CmLOX09,CmADH12,CmAAT1 and CmAAT2 were involved in the formation of aroma differences among different varieties,which might be the key genes leading to aroma differences.