Study On The Formation Mechanism Of Volatile Substances In Germinated Foxtail Millet Based On Lipid Metabolism

Foxtail millet is one of the oldest crops in the world,and it is alsoone of the major miscellaneous grains in China.Foxtail millet is consumed in a single way at present,and the germination process can increase the content of functional components in the millet and broaden its processing methods.The study of changes in volatile substances and their formation mechanisms during germination of grain is particularly important because of the special odor produced by the grain during the germination process.In this study,the changes in the physiological and biochemical properties,volatile components and lipid metabolites of the two varieties millet,"Jigu 39" and "Jichuang 1",during the germination process were investigated,and the relationship between differential lipids and volatile substances was preliminarily explored.The main results are as follows:During the 0-24h germination process,the soluble protein content of millet decreased,and the content of five free fatty acids including palmitic acid,stearic acid,oleic acid,linoleic acid and linolenic acid first increased and then decreased,and they were all within 18 h At the peak,the overall activities of lipase,lipoxygenase,hydroperoxide lyase,and alcohol dehydrogenase showed a trend of first increasing and then decreasing with the extension of germination time.Four extraction methods including-solvent extraction(LLE),solvent assisted distillation extraction(SAFE),simultaneous distillation extraction(SDE)and solid phase microextraction(SPME).were compared,and HS-SPME was selected as the optimal extraction method.The HS-SPME-GC-MS technique was further used to study the changes of volatile metabolites in the germination process of millet.The results showed that 32 and 28 volatile substances,mainly alkanes,olefins,aldehydes,esters,alcohols and ketones,were detected in "Jigu 39" and "Jichuang 1",respectively,during the germination process.Combined with multivariate statistical analysis,the differential volatile substances in "Jigu 39" and "Jichuang 1" are(E)-2-octadiene,tetradecane,(E)-2-nonenal and nonanal,respectively 3-octene-2-one,(E,E)-2,4-nonanedialdehyde,undecane,hexadecane 8 kinds and nonane,undecane,dodecane,tetradecane,3,5 kinds of 5-octadiene-2-ol.The non-targeted lipid metabolite profiles of millets during 24 h of germination were analyzed using ultra performance liquid chromatography-tandem quadrupole-time-of-flight mass spectrometry(UPLC-Q-TOF-MS).And then it was further combined with multivariate statistical analysis to screen and identify lipid metabolism markers of millets during germination.The results showed that after 24 hours of germination,a total of 600 lipids were identified in "Jigu 39" and "Jichuang 1",and 81 and 79 kinds of differential lipids in "Jigu 39" and "Jichuang 1" were respectively.Among them,linoleic acid has the largest difference and is the main lipid metabolism marker.The relationship between differential lipids and volatiles was investigated using a verification experiment.The pathway of volatile substance formation from linoleic acid is the gradual formation of(E)-2-octenal as well as 3-octen-2-one after the generation of 10-perhydroxyl linoleic acid from linoleic acid.In addition,during the germination process of millet,free fatty acids slowly produce volatile substances by the action of enzymes,while the content of free fatty acids and differential lipids is at an increasing stage,thus it indicated that there is a synergistic effect of free fatty acids with other types of lipids in the process of volatile substance production.