Study On The Formation Mechanism And Metabolism Law Of Main Quality Traits Of Vegetable Soybean

Vegetable soybean is a kind of value-added specialty soybean that are picked and eaten when the pods have not turned yellow and the grains are not fully mature.It is deeply loved by consumers and has high economic benefits.Nutritional quality(nutrient content and composition)and edible quality(sweet taste,umami taste,fragrance,et al.)are the main qualities of vegetable soybean,which are closely related to the composition and content of chemical components in the seeds.Therefore,it is necessary to analyze the chemical compositions and their formation in seeds.In this study,a non-destructive and rapid detection method of soluble sugar content in vegetable soybean was established by near-infrared spectroscopy.Based on the method,varieties with soluble sugar content in different intervals(TW292,X3 and SX6)were screened out for the following research.The differences of chemical compositions related to main quality among three varieties were studied.The formation of main quality and the changes of key enzyme activities during seed-filling period were detected.Finally,non-targeted metabolomics was used to analyze the differential metabolites and metabolic pathways during seed-filling period in order to fully understand the changes and regulation mechanism of key components in vegetable soybean.The main results are listed as follows:1.Establishment of a fast detection method of soluble sugar content in vegetable soybean by near infrared spectroscopy.Soluble sugar content of 100 vegetable soybean germplasms ranged from 2.86% to 9.41%.The root mean square error was 0.635,and the coefficient of determination was 0.8346.External validation of the prediction model was conducted,and the coefficient of determination and prediction mean square error were 0.8286 and 0.670,respectively.2.The contents of fat,protein,soluble protein,soluble sugar and total free amino acids of the 3 kinds vegetable soybeans ranged from 15.40% to 22.66%,35.36% to 39.35%,10.29% to11.60%,3.43% to 8.70% and 8.21 to 15.43 mg/g respectively.Soluble sugar and amino acid are the main differential chemical components,and the coefficient of variation was 0.42 and 0.34,respectively.TW292 had the highest sweetness score because of the highest soluble sugar content.SX6 had the highest umami response value of electronic tongue because of the highest content of free amino acids.A total of 41 volatile components were identified in the 3 kinds of vegetable soybeans,mainly including hexanal,nonanal,1-octen-3-ol et al.3.The content of fat,protein and soluble protein during the seed-filling period showed an upward trend.The content of soluble sugar showed a trend of increasing first and then decreasing,and the sucrose content was the highest.Sucrose phosphate synthetase catalyses the sucrose synthesis.Sucrose synthase breaks down sucrose at the early stage of seed-filling and synthesizes sucrose at the late stage of seed-filling.Acid invertase and neutral invertase catalyze the breakdown of sucrose,and showed the highest activity at the early stage of seed-filling.The content of free amino acids showed a trend of increasing first and then decreasing.Glutamine synthase catalyzes the reuse of protein and amino acid,and the activity showed a trend of increasing first and then decreasing.4.Based on non-targeted metabolomics,a total of 911 metabolites were identified in vegetable soybean,mainly including compounds with biological roles,lipids and phytochemical compounds.The metabolism of chemical components associated with main qualities changed with some regularity.In the seed-filling period,the content of tryptophan and cysteine increased through the biosynthesis of amino acids.The change of carbohydrate was mainly due to Dglucose-6-phosphate that involved in sucrose and starch metabolism.In the ripe period,from the perspective of amino acid changes,Aspartic acid and phenylalanine were synthesized through cyanoamino acid metabolism pathway in TW292.Meanwhile,the phenylalanine was accumulated through phenylalanine,tyrosine and tryptophan biosynthesis pathway in X3.Phenylpropane biosynthesis and phenylalanine metabolism were observed in SX6.From the perspective of carbohydrates changes,TW292 showed an increase in fructose content.The carbohydrates in X3 and SX6 are mainly focused on biosynthetic of secondary metabolites.