Study On Screening And Compounding Of Lactic Acid Bacteria Based On Fermentation Characteristic Of Commercial Starter Culture

With the improvement of living standards, the side of the health benefits of the body and has a special taste of fermented dairy products are popular with the public, and Sales showed an increasing trend year by year. The starter culture used in our country are mostly imported products, which greatly restrict the development of dairy industry in China. Our country has a rich microbial resources, which also provides a foundation for the development of fermentation strains isolated. In this study, we used the polymerase chain reaction denaturing gradient gelelectrophoresis(PCR-DGGE) to confirm the miroflora in starter culture. And using randomly amplified polymorphic DNA(RAPD) and traditional method, we successfully isolated all strains detected by PCR-DGGE. At the same time, we screened excellent Lactic Acid Bacteria in traditional dairy products of Yunnan(Yogurt, dairy fan and pickles) on the basis of fermentation characteristic of commercial starter culture, and the strains were studied in combination. Finally, we got the freeze dried powder through the optimization of the culture medium and the freeze drying protective agent. This research has important practical significance for the research and development of independent intellectual property rights of lactic acid bacteria, And for the Directed Vat Set production has laid a theoretical foundation. The main results were as follows:(1) Four strains of bacteria were isolated from starter culture. These inclued Streptococcus thermophilus CN-SR, CN-ST; Lactobacillus delbrueckii subsp. bulgaricus CN-B; Lactobacillus casei CN-L. By evaluating the fermentation characteristic of these strains, we found that the CN-ST acid production rate was fast and the content of acetaldehyde and butyl two ketone was the highest in cold storage of 1 d; The degree of post acidification of CN-SR was the lowest; CN-B had good viscosity characteristics; cold storage 20 d of these strains, the number of viable bacteria can still reach 108 CFU/mL; 50 generations of the acidification was stability. CN-B, CN-ST and CN-SR were selected as the main experimental strains.(2) By comparing with commercial bacterial strains in terms of acid production, viscosity, production of incense, number of live bacteria, stability and so on, we screened the B14 which is similar to the fermentation characteristics of CN-B, S1 which is similar to the CN-SR, S2 which is similar to the CN-ST.(3) By the determination of fermentation characteristics such as acidity, post acidification, production of viscosity, butyl two ketone content, acetaldehyde content and Sensory evaluation. We found that the optimal proportion is A4(B14:coccus(S1:S2=1:1)=1:50).(4) The lyophilizated stain powder was produced. The medium optimal formula of B14: Tomato juiee7.5%, CaCO3 0.075%, lactose 2% was added on the basis of culture medium MRS; the formulation of the potectants: trehalose15%, sodium erythorbate 3%, skim milk 7.5%, monosodium glutamate 1%. The medium optimal formula of S1 and S2: the basis of Skim milk culture medium is obtained by adding tomato juiee7.5%, malt extract 0.075%, lactose 2%; the formulation of the potectants: Trehalose10%, skim milk 10%, monosodium glutamate 2%, glycerol 1%.(5) By verifing the fermentation performance of the compound freeze-dried powder, we found there was no significant difference between the bacteria broth. The results proved that the strters prodced in our present study would be very promising as commercial starter culture for yogurt manufaeture.