Metagenomics Analysis Of Microbial Community Of Russian Bread Sourdough And Its Lyophilized Powder

Russian bread sourdough is a natural mixed strain leavening agent obtained from whole wheat flour or black flour,hop water,a small amount of salt,and adding fermented seeds.Traditional sourdough requires two to three fermentations to make Russian bread,it takes a long time,the operation is complicated,and the strains are unstable,resulting in differences in bread quality.This topic studies the change of microbial flora during the activation process of fermented seeds,reveals the period of rich fungi and bacterial communities,and analyzes the flora structure and metabolic pathways of sourdough using metagenomic technology during this period.Submitted to the GenBank database with registration numbers SRR9701328、SRR9701327.The micro-ecological group formed naturally by sourdough is stable and convenient to use,and the lyophilized powder of sourdough is developed and its effect on bread flavor texture.Because the sourdough is stored in the bakery for a long time,and the microorganisms are in a dormant state,it needs to be continued to form sourdough before use.Orthogonal experiments were used to optimize the conditions for continued seeding:12%bran content,20%hop water addition,and fermentation temperature of 24℃.The total number of colonies and the main components in sourdough for 48 h of continuous fermentation were studied.When fermented for 16 h,the total number of fungal colonies is 2.43×10~8 CFU/g,pH 5.14,starch content 65.7 g/100g,dietary fiber content 2.948 g/100g,protein content 10.82 g/100g,fat content 1.25 g/100g(the Period sourdough marked M1);When the total fermentation time was 32 h,the total number of bacterial colonies was 2.32×10~9 CFU/g,pH 4.01,starch content59.47 g/100g,dietary fiber content 2.803 g/100g,protein content 10.60 g/100g,fat content 1.14g/100g(the Period sourdough marked M2).In order to determine the structure of the flora when the total number of fungal and bacterial colonies is rich,sequencing of the sourdough doughs at M1 and M2 using metagenomics technology was performed to obtain 39881、42074 non-redundant gene sets,respectively.According to the comparison database M1 sourdough,21 phyla,276 genera,and899 species were identified,of which 74 bacterial species and 13 fungal species were more than 0.01%,The main dominant species of bacteria were Lactobacillus plantarum17.91%,Pediococcus pentosaceus 14.70%,Lactobacillus curvatus 9.25%,Lactobacillus sakei 6.56%;The main dominant species of fungi were Saccharomyces cerevisiae 8.57%,Saccharomyces bayanus 5.62%;According to the comparison database M2 sourdough,22 phyla,329 genera,and 1076 species were identified,of which 114 bacterial species and 12 fungal species were more than 0.01%,The main dominant species of bacteria were Lactobacillus curvatus 18.82%,Lactobacillus brevis 12.29%,Clostridium saccharobutylicum 9.23%,Lactobacillus fermentum8.92%,Pediococcus pentosaceus 8.83%;The main dominant species of fungi were Saccharomyces cerevisiae 4.28%,Pichia kudriavzevii 0.32%.The M1 and M2 sourdough metagenome gene sequences were compared with each database:M1 and M2 sourdough were obtained from 336 and 341 types of metabolic pathways respectively.At the same time,there were 30 significantly enriched differentially expressed genes.There are 6 ways in which the impact value is greater than 0.15.The COG annotation function of M1 and M2 sourdough is divided into 25 categories,and genes are distributed in 5enzyme lines.Collect the sourdough dough fermented for 16 h(M1)and 32 h(M2)and fermented with a protective agent(8%trehalose:4%glycerol=1:1),mix 1:3,freeze-dried thickness 0.8 cm,and dried for 24 h The freeze-dried sourdough was made into lyophilized powder,and its survival rate was 78.5%.Study on the flavor and texture of sourdough lyophilized flour and fast yeast fermentation bread.HPLC detection of organic acids showed that:lactic acid(241 mg/100g),acetic acid(29.6 mg/100g)and citric acid in lyophilized sourdough bread.The content of 24.2 mg/100g was higher than that of fast yeast bread,but the content of oxalic acid in yeast bread was higher(16.5 mg/100g).GC-MS was used to determine the flavor of bread.There were 22 kinds of fast yeast bread,37 kinds of yeast dry freeze-dried bread,and sourdough lyophilized bread with ethyl lactate(1.38%)to increase the caramel flavor and acetic acid of bread.Phenethyl(0.63%)imparts aromas such as bread apple,cocoa and whiskey.The sourdough lyophilized bread has higher hardness,stickiness,chewiness and resilience than yeast bread,cohesiveness and specific volume are lower than yeast bread,but there is no significant difference in elasticity;analysis by electronic tongue and electronic nose principal component analysis(PCA),Can well distinguish the taste and flavor of the two types of bread.