Effects Of Traditional Starter From Different Regions On Flavor Characteristics And Quality Of Steamed Bread

In this paper,the physiological indexes of traditional starters in different regions of China were compared and analyzed.The dynamic rheological properties of fermented dough in different regions were studied by rheometer.The quality characteristics of steamed bread with traditional starters in 14 regions were analyzed and the important factors affecting the quality of steamed bread were identified.The volatile compounds in fermented dough and steamed bread from 14 regions were studied by means of solid phase micro extraction(SPME)and GC-MS,and the results were compared by principal component analysis(PCA).Different kinds of fungi and bacteria were isolated from the traditional starters.The mixed samples of three lactic acid bacteria and one yeast were made,and the fermentation mechanism of the main volatile compounds in steamed bread made by mixed bacteria was studied preliminarily.The quality characteristics of fermented steamed bread with different bacteria and mixed bacteria were determined.The main conclusions of the research are as follows:1.Different regions of the traditional staters made in the fermentation process,the change trend of p H and TTA were similar,with the increase of fermentation time,dough p H value decreased,titratable acidity TTA increased gradually,until the dough fermentation maturity,the value of p H and TTA changes relatively slowly and become stable.The growth trend of yeast and lactic acid bacteria were similar in different regions during dough fermentation.The growth of yeast grew rapidly in the early stage of dough fermentation until the later stage of dough fermentation,and the growth of lactic acid bacteria was slow in the early stage of dough fermentation.After a short adaptation period,it entered a rapid growth period,and then showed a significant downward trend after the dough maturation.The fermentation parameters and rheological properties of the dough were different in different regions,and the specific volume,hardness and viscosity of the steamed bread were different.The difference of chewiness and sensory quality was significant(P < 0.05).p H and TTA were the important factors affecting the fermentation characteristics,physical properties and sensory quality of steamed bread at mature stage of dough fermentation.The steamed bread with the p H value between 4.24 and 4.89 at the mature stage of dough is of better comprehensive quality.2.Through the methods of extraction and analysis of the same from 15 kinds of fermented dough 223 volatile compounds were detected,including 59 esters(35.44%),60(28.91%),hydrocarbons 14 kinds of aldehydes(3.51%),11 acids(1.38%),16(7.28%)of vinyl material,19 alcohols(9.77%),11 kinds of ketones(1.15%),7 kinds of benzene ring(3.98%)and a small amount of ether compounds and aromatic substances(8.59%).The volatile compounds in the fermented dough of traditional starters in different regions mainly include esters,hydrocarbons,aldehydes,acids,alkenes,alcohols,ketones,benzene rings and a small amount of ethers,heterocyclic and aromatic substances.The main components are esters,hydrocarbons,aldehydes,aldehydes,acids,alkenes,alcohols and aromatic compounds in all regions.The total flavor of the dough prepared from different regions was similar,but there were some differences in the composition and quantity of volatile compounds.Using the methods of extraction and analysis of the same from the 15 steamed bread in 153 kinds of volatile compounds were detected,including 28 esters(12.97%),56(31.45%),hydrocarbons 10 kinds of aldehydes(11.10%),6 acids,9(1.62%)ene terpenoids(8.95%),10 alcohols(5.39%),6 kinds of ketones(1.09%),12(2.99%)benzene ring,heterocyclic and aromatic substances amount(24.43%).The main flavor compounds of steamed bread prepared by traditional starters in different regions are different.The main esters in the steamed bread numbered 1#/12#/13# are esters,the main components in steamed bread numbered 2#/3#/4#/5#/6#/7#/9#/10#/14#/CY were mainly hydrocarbon substances,heterocyclic and aromatic compounds in steamed bread numbered 8#,The main components of volatile compounds in steamed bread 12#were alcohols.The main contents of 11# steamed bread are alkenes.The species of volatile compounds in steamed bread from different regions were similar,but there were some differences in the composition and quantity of volatile compounds.3.3 forms of lactic acid bacteria and 3 forms of yeast strains were isolated from the traditional starters.A total of 6 kinds of lactic acid bacteria were identified as follows: Pediococcus pentosaceus,Lactobacillus fermentum,Pediococcus acidilactici,Lactobacillus crustorum,Lactococcus lactis,Weissella confuse.4 types of yeast,respectively Saccharomyces cerevisia,Wickerhamomyces anomalus,Saccharomyces cerevisiae,Saccharomycopsis fibuligera.The next step of the experiment was to select Pediococcus pentosaceus(P),Lactobacillus fermentum(F),Lactococcus lactis(A)and Saccharomyces cerevisiae(S).4.The dough was mixed with single bacteria,double bacteria,three bacteria and four bacteria respectively.The volatile compounds of dough was determined by GCMS.Compared with the flavor compounds in the S sample,the mixed fermentation dough contains more volatile compounds and higher relative content.The composition and content of volatile compounds in dough prepared by mixed fermentation with different strains were different to some extent.The volatile compounds in dough from different regions were analyzed by principal component analysis(PCA)and PCA diagram.It was found that strain F was helpful for the production of acid substances,A strains contribute to the production of alcohols,ketones,aldehydes and alkenes,P strain contributes to the production of aromatic substances.Compared with the dough fermented by single bacteria,the dough with mixed bacteria contains more esters and more kinds,which makes the dough flavor richer and stronger.5.pH and TTA were measured during the fermentation of dough mixed with different strains.The results showed that strain F had strong acid-producing ability and produced acid quickly but not for a long time.The acid production of A was lower than that of strain F,but the acid production rate of A was weaker than that of strain P,and the acid production rate of strain A was lower than that of strain F.S+F+A has the highest acidity and fast acid production.Compared with S+F and S+A combination,the TTA of the three bacteria fermented dough is lower.The acidity of S+F+P sample decreased mainly in the middle stage of fermentation,the acidity of dough was lower than S+F sample but higher than that of S+P sample.The acid production trend of S+P+A samples decreased steadily and lasted longer after 2 h,but compared with the other two kinds of three bacteria fermented dough,the acidity was the smallest,and the TTA of dough was higher than that of S+P,S+A.On the whole,F strains because of its strong acid-producing ability,it is easy to make dough acidification in fermentation process,and the acid production rate leads to serious destruction of dough gluten network and poor product quality.The internal structure of steamed bread prepared by A strain a was well integrated,which was supposed to be due to the fact that strain a could metabolize more carbohydrates,and its moderate acid-producing ability could make dough acidify moderately,thus having a positive effect on the structure of steamed bread.The acid production ability of P strain was relatively weak and had little effect on steamed bread quality,but it could significantly improve the color and color of steamed bread.