| Kumquat is popular because of its medicinal value.Now,kumquat is popular because of its unique flavor and has great market potential.However,there are few studies on the volatile aroma components of Kumquat.The formation of fruit aroma involves many ways of fruit development,which can reflect fruit quality to a great extent.In this study,kumquat in mature stage was taken as the research object.By optimizing the conditions of solid phase microextraction,the HS-SPME-GC-MS method of volatile aroma components of Kumquat was established,and the changes of volatile aroma components and nutritional components of Kumquat at five different harvest times were analyzed to determine the best harvest time.At the same time,the enzyme activities and RNA expression related to aroma formation of Kumquat were studied to further study kumquat Changes of aroma in different harvest time.The main results are as followsThrough single factor experiment,the experimental conditions of HS-SPME-GC-MS were optimized.Based on this,the response surface experiment was designed.The optimal experimental conditions were as follows: extraction time70?min,extraction temperature 40?℃,sample size 3.0?g.Under these conditions,the aroma components of three different varieties of Kumquat were determined,and a total of 76 aroma components were identified.Among them,Limonene content was the highest,accounting for up to 70%;according to the detected volatile components,OAV value of 23 volatile components was greater than 1,and the higher OAV value was Laurene,(d)-Limonene,Linalool,Decanal,Perillaldehyde,(z)-β-Ocimene,α-Pinene and Hexanal,which indicated that these substances contributed to the direct flavor of Kumquat.The contents of volatile compounds,hardness,color difference,soluble solids,titratable acids,flavonoids and total phenols in Kumquat harvested at five different times were detected and analyzed.The results showed that the hardness of Kumquat harvested with 160 DAF decreased significantly.The color difference index of Kumquat was inversely proportional to the harvest time,and increased with the delay of harvest time.The color difference index of 160 DAF samples was significantly higher than that of 140 DAF samples,and the color difference index exceeded 0.Compared with the harvest time of 140 DAF,the soluble solids of 150 DAF increased significantly.The change trend of titratable acid is consistent with that of hardness.The change trend of flavonoids in Kumquat samples was similar to that of total phenols,both of which showed an upward trend at first and then a downward trend.The highest point is at 150 DAF.The variety of aroma components was the most abundant in Kumquat harvested at 150 DAF,and the content of main aroma components was the highest,and gradually decreased at 160DAF-180 DAF.The content of Limonene reached the highest value at 150 DAF,and decreased by more than 60% at 160DAF;the main aroma components such as Linalool,Myrcene and Hexene also showed a similar trend.The activities of HPL,LOX,ADH and AAT were detected by kit.The activities of LOX,HPL and AAT first increased and then decreased,which was consistent with the change trend of Hexyl-2-enal,Octanal and esters.A total of 74402 single gene clusters were obtained by RNA sequencing.The differentially expressed genes DN1606c0g1,DN20410c0g1 and DN2938c0g2,DN7318c0g1 related to the synthesis of terpene aroma precursors were up-regulated and then down regulated,which were related to the change of terpene aroma content.The two differentially expressed genes,DN12658c0g1 and DN21912c0g1,encoding LOX,were significantly up-regulated at 150 DAF.The gene DN7018c0g1,encoding HPL,was significantly up-regulated at 150 DAF and down regulated at160DAF-180 DAF.The high expressed genes,DN12674c0g1 and DN6834c0g1,encoding ADH,were down regulated at 140DAF-170 DAF.In order to provide a theoretical basis for editing kumquat genome and regulating kumquat aroma formation through genetic engineering. |
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