Analysis Of Sour Dough Microorganisms Based On High-Throughput Gene Sequencing And Development Of Compound Fermented Steamed Bread

As a traditional fermented food,sour dough steamed bread appeared in China very early and has a long and far-reaching history.Compared with single yeasts fermentation in industry,the traditional sour dough fermentation system contains not only a variety of yeasts,but also a large number of lactic acid bacteria.Through the joint action of yeast and lactic acid bacteria in sour dough fermentation,lots of substances affecting the overall flavor of steamed bread were produced,so the taste of sour dough steamed bread is richer and more unique.However,the production of sour dough steamed bread has not been industrialized.At present,most of the sour dough steamed bread on the market are sold by individual shops.The main reason for this phenomenon is that the production process is not standard and the products are uneven,the safety and controllability is poor,and there is a large amount of harmful bacteria,the fermentation time is long and the cost is high.Therefore,it is urgent to find out the distribution of microorganisms in sour dough and make high-quality products by scientific means.In the evaluation of steamed bread,we mostly use the traditional sensory evaluation method,which is easily affected by human subjective factors,resulting in great uncertainty in the evaluation results.On the basis of the above problems,the research results of this paper are as follows:（1）The high-throughput gene sequencing technology was used to analyze the microflora diversity of three kinds of sour dough samples with good flavor.The results showed that the main bacterial phylum were Firmicutes,Bacteroidota,Actinobacteriota,Deinococcota,and the main fungal phylum were Ascomycota and Basidiomycota.By using the abundance maps and Heatmap at the species level of the three kinds of sour dough,we can know that most of the bacteria contained in the three kinds of sour dough are lactic acid bacteria,and the fungi contained in the three kinds of sour dough are mainly yeasts,but it still contain a certain amount of pathogenic bacteria,such as Fusarium and Mold,which provides a theoretical basis for the scientific and safe production of sour dough steamed bread.Among them,the main LAB are Leuconostoc＿pseudomesenteroides＿g＿Leuconostoc,Lactobacillus＿paracasei,Lacto-bacillus＿plantarum＿g＿Lactobacillus,Lactobacillus＿helveticus,Weissella＿cibaria,Lactobacillus＿songhuajiangensis and Lactobacillus＿brevis＿g＿Lactobacillus.In the three samples,the main yeasts are Saccharomyces＿cerevisiae,Candida＿parapsil-osis and Pichia＿kudriavzevii.Two strains of fungi isolated from sour dough were identified as Saccharomyces cerevisiae and Pichia＿kudriavzevii,which can be used as compound fermentation strains.（2）Sixteen different kinds of steamed bread with good quality in the market were collected,and their specific volume,L-value,hardness,chewiness,gumminess,elasticity,cohesion,stickiness and recovery were measured,and the physical properties were analyzed by cluster analysis and correlation analysis.The results show that hardness,chewiness and gumminess are grouped into the same category,and the attributes can replace each other.Elasticity,cohesion and resilience can be classified into the same category,and the attributes can also replace each other.Through PLS analysis and correlation analysis,L-value,specific volume,hardness,elasticity and stickiness were selected as the main indexes in the quality evaluation of steamed bread.The score formula of steamed bread which can replace the sensory evaluation of steamed bread is obtained by principal component analysis:Y=0.504X₁+0.445X₂-0.481X₃+0.430X₄+0.128X₅,in which X₁represents L-value,value range is 74.47 to 83.48,X₂represents specific volume,value range is 2.48 to3.42 m L/g,X₃represents hardness,value range is 511.33 to 1856.56,X₄represents stickiness,value range is 1.05 to 7.17,X₅represents elasticity,value range is 0.88 to0.92.In order to make the score positive,let Z=(Y-Y_min)/(Y_max-Y_min)be the final score formula.（3）The effects of fermentation temperature,bacterial concentration and fermentation time on the production of steamed bread by Saccharomyces＿cerevisiae were studied.On the basis of that,three gradients were selected for each factor.Through orthogonal experiment,the best combination conditions for Saccharomyces＿cerevisiae to make steamed bread were obtained as follows:the fermentation temperature was 34℃,the bacterial concentration was 7×10⁷cfu/m L,the fermentation time was 4.0 h.Mainly Saccharomyces＿cerevisiae,the effects of different concentrations of Pichia＿kudriavzevii,Lactobacillus＿paracasei and Lactobacillus＿plantarum＿g＿Lactobacillus on the production of steamed bread by compound fermentation were studied.Through single factor test and orthogonal test,the optimum fermentation parameters were obtained as follows:the concentration of Pichia＿kudriavzevii was 7×10⁷cfu/m L,the concentration of Lactobacillus＿paracasei was 3×10⁸cfu/m L,the concentration of Lactobacillus＿plantarum＿g＿Lactobacillus was 3×10⁸cfu/m L.