Study On The Flavor Characteristics Of Steamed Breads With Different Starters

Steamed bread is a traditional staple food in China,and it plays an important role in the daily diet of people in northern regions.To a certain extent,flavor which is as one of the important sensory attributes of steamed bread,determines the consumer’s choice of food.The flavor compounds in steamed bread mainly depend on the type and performance of the starter used.Yeast and lactic acid bacteria are the main microorganisms.Metabolism and its enzyme transformation of microorganisms are considered as important synthetic pathways for flavor compounds.On the one hand,yeast converts fermentable sugars in flour into ethanol,carbon dioxide or other small molecule compounds through sugar metabolism;on the other hand,it can also convert amino acids into flavor compounds such as alcohol and acid through the Ehrlich pathway.On the one hand,sugars are transformed into lactic acid and other alcohols,esters and other flavor compounds by sugar metabolism of lactic acid bacteria;on the other hand,they can also degrade oligomeric peptides into amino acids by secreting proteases and convert them into aldehydes,ketones,and esters through a series of reactions to improve products flavor.In this study,yeast,jiaozi,and lactic acid bacteria of protease-producing were selected as steamed bread starters.In this study,the active yeast,yeast and screened proteaseproducing lactic acid bacteria were used as steamed bread starters.The effects of different fermentation agents on the volatile flavor substances of steamed bread were investigated by regulating the types of raw materials,starter types,bacterial phase composition,and fermentation process.The findings are as follows:(1)In order to study the change of flavor of different wheat flour in the process of making yeast steamed breads,the flour,whole wheat flour and lightly ground flour were used as raw materials,and the instant active dry yeast was used as a starter to study the volatile components of wheat flour,dough and steamed breads.The results show that wheat flour,dough,and steamed bread mainly contain six types of compounds such as hydrocarbons,alcohols,ketones,aldehydes,esters,and heterocycles.During the processing of steamed bread,alcohols,aldehydes,ketones,and Heterocyclic changes are most obvious.A total of 34 volatile components were detected in flour,light-milled flour and whole-wheat flour.Hexanal and nonanal are characteristic substances in flour;hexanal,nonanal and 1,3-dimethylbenzene are light-milled Characteristic substances in flour;hexanal,nonanal,ethanol,o-xylene are characteristic substances in whole wheat flour.During the dough formation process,the aldehydes(hexanal and nonanal)contents of the three wheat flour doughs all increased significantly;the ketones in the flour did not increase significantly,and the ketones(2-octyl)in the two whole-wheat flours Ketone,2-heptanone)increased significantly.During the dough fermentation process,the relative content of alcohols(3-methyl-1-butanol,1-hexanol)in the three wheat flour doughs increased,and 1-pentanol was added to the two whole-wheat flours.The relative content of similar substances(hexanal and nonanal)decreases.In the steamed bread cooking stage,the relative content of ketones(6-methyl-5-hepten-2-one)in the three steamed breads decreased,and the relative content of heterocyclics(2-pentylfuran)increased.The relative content of alcohols(3-methyl-1-butanol)in the two bran steamed breads increased.A total of 33 volatile components were detected in gluten-free flour,lightly ground flour and whole wheat flour steamed breads.Hexanal and 2-pentylfuran are the characteristic substances in flour steamed breads;3-methyl-1-butanol,2-Pentylfuran is a characteristic substance in light-steamed steamed breads;hexanal,3-methyl-1-butanol,2-pentylfuran are characteristic substances in whole-wheat steamed breads.(2)In order to explore the influence of different yeasts on the flavor of steamed breads,the composition of corn yeasts from different origins and the volatile components in the steamed breads prepared from them were studied.The results showed that a total of 50 and 37 volatile flavor substances were detected in yeast and steamed breads,including alcohols,ketones,aldehydes,esters,heterocycles,acids,hydrocarbons and other compounds.2,3-butanedione,acetoin,hexanal,nonanal,2,3-butanediol,phenylethanol,4-methyl-1-pentanol,2-pentyl-furan,tetramethylpyrazine,acetic acid,ammonium acetate are characteristic substances of Jiaozi.Ethanol,3-methyl-1-butanol,hexanal,hexyl chloroformate,2-pentylfuran,methoxyphenyl oxime are Characteristic substances of steamed breads maded in Jiaozi.(3)In order to explore the structural composition and differences of microbial flora of different enzymes,corn yeasts from different origins were collected,and high-throughput sequencing methods were used to reveal the differences in microbial diversity and structural composition of different enzymes.The results showed that the microbial flora structure of different enzymes was complex and the types of bacteria and fungi were very different;in terms of bacterial composition,mainly Lactobacillus,Pediococcus,Acetobacter;in terms of fungal composition,mainly The genus Saccharomyces and Candida are dominant,and some enzymes also exist in the genus Fusarium and Aspergillus.The bacteria in the enzyme have similar metabolic patterns,especially Amino Acid Metabolism,Carbohydrate Metabolism and Membrane Transport.(4)In order to study the influence of protease-producing lactic acid bacteria on the flavor of steamed bread,the protease-producing strains were screened from corn yeast by traditional culture methods,and combined with colony morphology,physiological and biochemical characteristics and molecular biological methods,two strains were identified as proteaseproducing lactic acid bacteria,respectively Lactobacillus fermentum and Pediococcus acidilactici.Two strains of lactic acid bacteria were mixed with yeast to prepare two different mixed fermentation fermented steamed breads,and the volatile flavors were compared with a single yeast bun.The results showed that three kinds of steamed breads prepared from a single yeast,L.fermentum and Pediococcus acidilactici were detected 25,32,and 29 volatile flavor compounds,hexanal,nonanal,and 2-pentylfuran are the components with higher content in the three types of steamed breads.Relative to a single yeast steamed breads,steamed breads maded with L.fermentum increased 2-hexyl-1-decanol,trans-2-dodecen-1-ol,heptanal,acetoin,5-ethyldihydro-2(3H)-Furanone,hexyl acetate and other flavor substances.Steamed breads maded with Pediococcus acidilactici added phytol,heptanal,acetoin,5-pentyl dihydro-2(3H)-furanone,hexyl phenylacetate and other flavor substances.