Optimization Of The Process Bean Curd Solidified By Lactobacillus Fermenting Acid Slurry And Preliminary Mechanism Of The Solidification

Acid liquid bean curd in our country has thousands of years of processing history.Acid liquid is the waste water produced in tofu making process--tofu whey is acidified by natural fermentation,and using acid liquid as coagulant makes tofu more fragrant.However,the traditional acid liquid is a product of natural fermentation,which is greatly affected by environmental factors.It is difficult to control the acidity of the acid liquid,resulting in a very unstable quality of the acid liquid bean curd produced.On the other hand,in the natural fermentation process,in addition to bacteria outside there are many spoilage bacteria,there are security risks.Thus,in this study,the use of high-throughput sequencing technology and traditional plate counting method to analyze microbial flora and dominant genus in natural fermented acid slurry,filtered out a dominant acid slurry fermentation bacteria,optimizing the fermentation conditions and the process of making tofu;then,by analyzing the main components of the pure acid slurry,the solidification mechanism of the pure acid slurry bean curd was probed by the simulated solution method.It's designed to provide a theoretical basis and technical reference for the green and safe production of acid liquid bean curd.1.Analysis of the microbial flora and dominant bacteria in acid slurry by traditional plate counting method and high throughput sequencing technology.First of all,using the traditional plate colony counting method to determine the bacteria is the dominant genus of the three different sources of acid slurry.Then,using the high-throughput sequencing technology to analyze the bacterial community of natural fermented pulp,it was found that the bacterial community of the three groups of pulp possessed the similar richness and diversity: at the phylum level,Firmicutes is the most abundant phylum,accounting for more than 67%,followed by Proteobacteria.At the genus level,Lactobacillus is the most abundant genus,followed by Acetobacter.Thus,it was confirmed that Lactobacillus was the dominant genus of natural fermented acid slurry.2.Screening and identification and determination of growth curve of dominant bacteria in acid slurry.Respectively dissolved calcium,pH and lactate production as indexes,by plate counting method and high performance liquid chromatography(HPLC),after preliminary screening and re-screening,five strains of lactic acid bacteria were isolated and purified from natural fermented tofu acid slurry,in which strain YQ336 had the most lactic acid production.According to its strain morphology,colony morphology,physiological and biochemical test results and 16 S rDNA sequence analysis were carried out,the strain was identified as Lactobacillus casei and named as Lactobacillus casei YQ336.The strain entered the stationary phase after 22 h and entered the decay stage after 40 h.The maximum total acid yield reached 33.17g/L at 48 h,and the lowest pH reached 3.35 at 60 h.3.Optimization of fermentation conditions of L.casei YQ336.Taking acid production and cell density as indexes,the fermentation conditions of L.casei YQ336 were optimized by single factor experiments and response surface experiments.The optimum fermentation conditions were as follows: fermentation time 48 h,fermentation temperature 37?,initial pH6.0,inoculation amount 3%,carbon source was glucose,adding 5%,under this condition,lactic acid production was 28.81 g/L,total acid yield was 34.25 g/L.4.Optimization of processing Conditions of bean curd solidified by L.casei YQ336 fermenting acid slurry.Taking the hardness,elasticity,adhesiveness,chewiness and sensory score as indexes,the optimum technological conditions of bean curd solidified by L.casei YQ336 fermenting acid slurry were determined by single factor and orthogonal experiment as follows: the pH value of the syrup was 3.6,the amount of the acid pulp was 11%,the pressing strength was 1000 Pa and the pressing time was 30 min.5.Preliminary study on the mechanism of soybean protein solidified by L.casei YQ336 fermenting acid slurry.Using simulated solution method,the results show that: lactic acid produced by fermentation of L.casei YQ336 was the main reason for the coagulation of soy protein.The addition of lactic acid reduced the pH of soymilk to the isoelectric point of soy protein to form gel,at the same time,the metal ions contained in soybean and water promote the polymerization between the peptide chains,making the gel structure more compact.