Studies On Preparation Of Sourdough Starter And Its Mechanism Of Improving Bread Dough Quality

Compared with common bread,sourdough bread has many advantages.Many studies have shown that sourdough bread can improve the baking properties,flavor and shelf life of bread.However,the existing sourdough production method could not meet the needs of industrial production,because of instability,low yield and low quality.It was found that the quality of natural fruit strains was better than that of cereal sources and there were few related studies.Therefore,in this paper,sourdough was screened and prepared into a starter culture with high storage activity through the study of drying protective agent.The application quality of starter culture was studied.Finally,the mechanism of improving bread quality by sourdough starter was studied,and was explained from the aspects of the microstructure of gluten protein and bread macrostructure.The main research contents and results were as follows:Firstly,fruit sourdoughs were cultivated,and the high quality sourdoughs were selected based on their baking quality,texture quality and other applied qualities.The results showed that the bread prepared by grape sourdough(gs)had the best specific volume(4.79 cm~3/g),porosity(41.77%)and hardness(175 g).On this basis,the drying survival rate and storage activity were used as indexes to study the combination of drying protectants.Finally,two better protective agent formulations were obtained by orthogonal experiment:1.Freeze-dried the dominant pure bacterial solution(FDS),skim milk 35%,maltodextrin 7.5%and trehalose 25%,and the drying survival rate was about 93%.2.Spray dried sourdough germ whole(SDD),skim milk 35%,maltodextrin 10%and trehalose 20%,and drying survival rate was about 90%.Meanwhile,it was found that the storage activity of spray-dried starter decreased rapidly(about67%after 60 days),while that of freeze-dried starter was slower(about 75%after 60 days).Secondly,after the preparation of sourdough starter,the application quality was studied.Compared with blank breads,the breads prepared with sourdough starter culture had better texture properties,and the breads prepared with FDS had higher specific volume(5%),lower hardness(25%)and better aging resistance(7.8%)than those prepared with spray-dried sourdough culture(SDDB).The analysis of the volatile compounds in different kinds of bread showed that the characteristic volatile compounds of sourdough bread were hexanoic acid,ethyl ester,2-heptanone,2-undecanone,triacetin,and 2-nonanone.There was no significant difference between the volatile substances of FDSB and SDDB,and the overall flavor reduction degree was more than 80%.The study on the fermentation process of sourdough starter found that the total contents of alcohols and esters increased with time,while the aldehydes and ketones had two peaks.In general,the sourdough leavening agent effectively improved the tissue characteristics of bread and had higher retention of sensory characteristics.Finally,the mechanism of improving the properties of dough tissue by sourdough starter was studied.It was found that lactic acid was the main difference of different starters,and a small amount of lactic acid could change the secondary structure of protein,expose more side chain groups,provide more space for cross-linking of disulfide bonds,which increase the content of disulfide bonds(from 32μmol/m L to 36μmol/m L).When the content of lactic acid increased continuously,β-folding decreased the space crosslinking chance,and the disulfide bond content decreased to 25μmol/m L.By measuring the degree of protein hydrolysis,it was found that the degree of protein hydrolysis increased with the content of lactic acid,which should be unfavorable to the formation of disulfide bonds,it is proved that the secondary structure change has great influence on disulfide bond formation.Then the changes of bread quality induced by the change of gluten network structure were analyzed by bread quality,porosity and confocal laser scanning.In conclusion,the sourdough starter prepared in this study could effectively improve the quality of bread and retain the characteristic flavor,and the organic acids introduced by sourdough starter culture can promote the change of protein structure and improve the quality of dough and bread.It provides a reference for the industrial production and application of sourdough starter and has a large market for application.