Distinct Changes Of Characteristic Compounds In Garlic During Growth And Storage Based On Metabolomics

Garlic,an important spice and folk medicine worldwide,is rich in functional and nutritional components and has important health benefits for human being.China is the largest garlic producer and exporter worldwide with a wide planting area and numerous varieties.However,the characterization of garlic produced from China of different regions and varieties in terms of organosulfur compounds and amino acids has not yet been clear until now.Besides,there is no study about the relatively overall changes of garlic biochemical composition in different development and storage stages to our knowledge.Therefore,targeted and nontargeted methods for the analysis of characteristic component in garlic were developed in the present study.Then,the compositional differences in garlic among different provinces and varieties as well as the metabolic profile and transportation pattern of metabolites in garlic at different development and storage time were studied based on the developed method combined with metabolomics.The study was designed to provide preliminary data for garlic production and consumption.The main contents and result are as follows:Firstly,a newly developed analytical method with a rapid and simple sample preparation to determine 7 flavor precursors and 21 amino acids simultaneously by UHPLC-MS/MS was developed.The method was applied to other four tissues of garlic,including leaf,pseudostem,bulb wrapper,and clove skin.The results indicated that the method was suitable for the analysis of other four tissues except for Met.At the same time,the UHPLC Q-Exactive Orbitrap MS method for nontarget analysis of characteristic components in garlic was established,and a part of metabolites in garlic could be qualitatively analyzed and semi-quantified in garlic by this method.Secondly,the levels and compositional differences of allicin,7 flavor precursors,and 21 amino acids in garlic among 242 samples from 6 provinces were investigated.Results indicated that Alliin,Methiin,GSAC and Arg were abundant in garlic.The levels of organosulfur compounds and amino acids varied both between north and south area and between 6 provinces in China.Trp,GABA,SMC,Tyr,Arg and Thr were the most important biomarkers for garlic in different regions.These results could provide preliminary data for breeding programs,as well as a reference of the raw material selection for garlic deep-processing products.Thirdly,the regulatory mechanism and accumulation pattern of metabolites in clove during growth in SD(J3,J4,and BP)and HLJ(ZP)were studied;additionally,other garlic tissues,including leaf,pseudostem,bulb wrapper,and clove skin,were also subjected to metabolite profiling to analyze the transportation of metabolites in different tissues during growth,which may give a deep insight for the quality formation of clove.Results showed that the accumulation pattern of metabolites during growth in three varieties of garlic in SD was similar,but obviously distinct from that planted in HLJ.The changes of metabolites highlighted the importance of super-pathway of allium flavor precursors and metabolism for amino acids during garlic growth.At the beginning of garlic bulb development,metabolites mainly synthesized in green leaf,and transported to the storage organ at the same time.After that,?-glutamyl peptides and other metabolites were transported from all the parts of plant to cloves when the leaves began to wither.Reliable OPLS prediction models based on agro-morphological traits for the levels of functional components were also provided.These results play an important role for the comprehensive utilization of garlic by-products,and also give a new idea for the estimation of garlic quality and confirmation of the best harvest time.Fourthly,the changes of metabolites and regulatory mechanism in garlic under room and low temperature were analyzed,and reliable OPLS prediction models for the storage time at low temperature were also provided.Results indicated that garlic began to sprout when its dormancy period was ruptured at room temperature,and a higher ?-glutamyl transpeptidase activity was observed in sprouting garlic compared with dormant bulbs.Therefore,a large portion of ?-glutamyl peptides was converted into corresponding free amino acids under ambient conditions when the dormancy was ruptured,which is totally in contrast to the tendency of garlic clove during growth.Cold storage could retard sprouting of garlic cloves,and forced the garlic to keep in dormancy.Therefore,the change of metabolites was much moderate under cold storage.SMC,Phe,and Gln were three important indicators for the prediction of storage time in OPLS regression models.These results would provide beneficial information to store garlic in a scientific and reasonable way and make full use of garlic during storage.