| As the functional grain,foxtail millet has attracted more and more public attention.Cooking and eating quality is one of the most direct ways for consumers to assessthe quality of foxtail millet.Even though there are abundant millet germplasm resources in China,the nutritional quality and eating quality vary greatly among them.Therefore,it is of great significance to the millet industry to excavate the characteristic nutritional components,especially the effective functional components,and to screen for varieties with better cooking and eating quality.In this study,Jingu 21,an elite millet variety,and Niumaobai,a land race,were selected as the research materials.On the basis of understanding the main cooking quality indexes,the lipid change patterns of the millets before and after cooking were analyzed for the first time by using lipidomics technology.The accumulation characteristics of metabolites during grain filling in the millets were preliminary explored by using metabolomic technology,as well as the related metabolic pathways were analyzed with metabolomics-transcriptome.The main results are as follows:1.Twelve millet varieties were evaluated by tasting the millet porridge and observing the millet colour,resulting in Jingu 21(yellow millet)as the best taste quality and Niumaobai(white millet)as the worst.Analysis of their cooking and eating quality indexes were then carried out.(1)The analysis of millet gelatinization characteristics and solid content of millet porridge showed that,except the breakdown value,the peak viscosity,hot viscosity,final viscosity,consistence value and the other indexes of Jingu 21 were lower than those of Niumaobai,indicating that the eating quality of Jingu 21 was better than that of Niumaobai and harder to gelatinize during cooking,but the millet porridge preservation quality was worse than that of Niumaobai.The solid content of Jingu 21 millet porridge was significantly higher than that of Niumaobai,which was close related to the better taste of the millet porridge.(2)Fatty acid composition in foxtail millet varieties including Jingu 21 and Niumaobai of four representative millet colours of was analyzed in the study.The results showed that the fatty acid in themillet was mainly composed of seven components,among which linoleic acid was the main fatty acid,followed by palmitic acid,stearic acid and oleic acid;Linolenic acid,arachic acid and docosanoic acid accounted for a small proportion in millet.The content of unsaturated fatty acids in the Jingu 21 and 2white millet varieties(Niumaobai and Zhishenggu)was relatively high,whereaas that in green millet varieties(Daqinggu and Lumiqinggu)was relatively low.(3)The analysis of cooking aroma in the millet porridge of Jingu 21 and Niumaobai showed that Jingu 21 had more rich and modified aroma components than Niumaobai.There were 13 characteristic flavour components in the millet porridge.Among them,trans,trans-2,4-decadienal,hexanal,1-octen-3-ol,octanal,nonanal,(E)-2-nonenal,nonanol and dodecanal were likely to make great contributions to the aroma of millet porridge;Heptanal,naphthalene and undecanal might be considered to harmonize the overall flavour of millet porridge;2,10-Dimethyl-5,9-undecadien-2-one and decanal may be important or harmonize the overall flavour of millet porridge.2.The lipid metabolites and lipid change patterns before and after cooking in the millets of Jingu 21 and Niumaobai were analyzed in the study.The main results were as follows:(1)A total of 30 lipid subclasses,which included 657 lipid molecules,were identified from the millets of Jingu 21 and Niumaobai by non-targeted lipid metabonomics technology.The results showed that the main lipid components in the millet were triglyceride(245 kinds),diglyceride(61 kinds),phosphatidylcholine(59 kinds).In addition,lysophosphatidylcholine,cephalin,phosphatidic acid,ceramide,phosphatidylinositol,phosphatidylglycerol,lysophosphatidylcholine and lysophosph-atidylglycerol were relatively high in the millets,whereas the other lipids were relatively low.(2)The analysis of the changes of lipid metabolism before and after cooking showed that different millet varieties had differential lipid molecules;The content of lipid molecules in raw millet was the highest,followed by cooked millet,and the content of lipid molecules in the liquid of the porridge was the lowest;The raw millet and the cooked millet contained different lipid compounds with high contents.The phospholipid and phosphatidylserine in the cooked millet were much higher than that in the raw millet.(3)Comparing the main differences of lipid molecules between Jingu 21 and Niumaobai in the raw millet,the cooked millet and the liquid of the millet porridge,we found that each of them in the millet of Jingu 21 and Niu Maobai had different lipid molecules that showing higher contents.There were more and higher contents of lipid molecules in the raw millet and the liquid of the millet porridge of Jingu 21(especially lipids in the liquid porridge reached to 21 kinds)than Niumaobai,whereas Niumaobai had moreand higher contents of lipid molecules only in the cooked millet than Jingu 21.The results showed that the changes and chemical reaction of lipid metabolites in the millets of Jingu 21 during cooking maybe more obvious than those in Niumaobai,which may lead to higher content and richer aroma in Jingu 21 during cooking,making its porridge taste better.3.The accumulation patterns of metabolites in Jingu 21 and Niumaobai millet at the early and late grain filling stages were analyzed.The main results were as follows:(1)A total of 554 metabolites,including 220 primary metabolites and 344 secondary metabolites,were identified in the millets for the first time by non-targeted metabolomics.These metabolites belong to 21categories: organic acids and their derivatives,phenol amines,amino acids and their derivatives,nucleotides and their derivatives,carbohydrates,hydroxyl cinnamyl derivatives,quinic acid and its derivatives,flavonoids,lipids,benzoic acid derivatives,nicotinic acid and its derivatives,choline,vitamins,alkaloids,alcohols and polyols,tryptamine and their derivatives,plant hormones,coumarins and their derivatives,indole and its derivatives,pyridine,terpenoids and others.Among them,flavonoids are the largest group(117 kinds),including flavone carboglycoside,flavone,flavonol,flavone-lignan,flavanone,isoflavone,catechin and anthocyanin.Some of these secondary metabolites have medicinal functions.(2)By analyzing the metabolites in the millets of Jingu 21 and Niumaobai at the early stage of grain filling,153 kinds of differential metabolites were found,which mainly existed in the biosynthesis pathway of flavonoids and flavonols,lysine degradation pathway,phenylalanine metabolism pathway,arginine and proline metabolism pathway and aminobenzoic acid degradation pathway.Cysteinylglycine,ferulic choline,4-hydroxy-7-methoxycoumarin-beta-rhamnoside and tricin 4’-O-(β-guaiacylglyceryl)ether-O-rutinoside were the specific differential metabolites at the early stage of grain filling of Niumaobai;Chrysoeriol O-sinapoylhexoside,13-Hp OTr E(r),4-ethylbenzoic acid,disinapoyl hexoside,Orobol(5,7,3’,4’-tetrahydroxyisoflavone),C-hexosyl-apigenin O-pentoside were the specific differential metabolites in Jingu 21.In addition,23 specific differential metabolites in Jingu 21 and Niumaobai were only found at the early stage of grain filling.(3)By analyzing the metabolites in the millets of Jingu 21 and Niumaobai at the later stage of grain filling,145 kinds of differential metabolites were found,which mainly existed in the biosynthetic pathways of phenylpropane,isoflavone,flavonoid and flavonol.Besides,tricin 4’-O-(β-guaiacylglyceryl)ether-O-rutinoside,catechin,methyl indole-3-acetate,gibberellin 15,N-feruloyl tyramine,4-hydroxy-7-meth oxycoumarin-beta-rhamnoside and 6-hydroxymethylherniarin were the specificdifferential metabolites in the late stage of grain-filling of Niu Maobai;13-Hp OTr E(r),chrysoeriol O-sinapoylhexoside,C-hexosyl-apigenin O-pentoside,xylitol,luteolin,2’-hydroxygenistein,disinapoyl hexoside and chlorogenic acid methyl ester were the specific differential metabolites of Jingu 21.In addition,17 specific differential metabolites in Jingu 21 and Niumaobai were only found at the late stage of grain filling.(4)By analyzing the accumulation characteristics of metabolites in the early and late stages of grain filling,a total of 108 differential metabolites were found in common between Jingu 21 and Niumaobai,78 and 72 metabolites were found specific to each variety.Combining with the classification map of KEGG metabolic pathways,55 metabolic pathways were at work in the millets of Jingu 21 and Niumaobai during grain filling,mainly about the primary metabolism of regulating physiological activities and secondary metabolism of response to environmental stimulations.In addition,there were 24 unique metabolic pathways only existed in the millets of Jingu 21 and 10 in the millets of Niumaobai,which may be related to their quality differences.4.Differential metabolites enriched in flavonoid biosynthesis pathway and phenylpropane biosynthesis pathway were analyzed by combining metabolomics-transcriptome.The main results are as follows:(1)In the metabolic synthetic branch pathway from naringin chalcone to chrysoeriol,except for apigenin that showed no significant difference in Jingu 21 and Niumaobai,the contents of the other five substances in Jingu 21 were higher than Nium Maobai.Combined with transcriptome analysis,10 key genes were identified,they were CHI(Seita.9G034700),CYP75B1(Seita.6G057600,Seita.6G171400),FNSI(Seita.9G342600,Seita.7G210600,Seita.9G561700,Seita.7G210500)and F3’OMT(Seita.8G1700,Seita.7G073700,Seita.8G1700).(2)In the metabolic synthetic branch pathway from sinapic acid to syringin,the content of sinapinaldehyde in Jingu 21 was much higher than Niumaobai,whereas the content of syringin was significant lower,and there was no significant changes on the content of sinapic acid and sinapinol in the two millet varieties.Combined with transcriptome analysis,4 key genes were identified,they were CCR(Seita.2G147600),CAD(Seita.2G199 100,Seita.6G026000,Seita.7G049 900). |
