Strain Screening And Preparation Of DVS Bacillus Natto Starter

As a traditional fermented food Natto is more and more concerned with its rich nutritional value and variety of healthy functions. It's significant for promoting the level of production of natto and predigesting the production process to research and development Direct Vat Starter (DVS) Bacillus natto starter. In this paper, the nicer Bacillus natto was isolated, the mutiplication conditions be explored and the medium composition be optimized, centrifugation conditions were screened, drying way and cryoprotectants was studied, fermentation performance and storage stability were determined.Firstly, in order to prepare DVS Bacillus natto starter, four predominant strains were sieved from Natto. By comparing the ability of tolerance and the capability of enzyme producing with Bacillus natto preserved in our laboratory, one of the most predominnant strain was sieved.Secondly, single factor experiments to study carbon and nitrogen sources impact on grow of Bacillus natto. six levels of two-factor completely randomized design to compare different carbon and nitrogen ratio impact on growth of Bacillus natto. L9(34) orthothgonal experiment is used to study ion composition impact on the growth of Bacillus natto. The best results were as follows:sucrose 1%, Peptone from soybean 2%, K2HPO4:KH2PO4= 0.3%:0.1%, MgSO4=0.05%, CaCl2=0.02%. Single factor experiments investigated the temperature, initial pH, inoculum size and medium volume impact on the growth of Bacillus natto.The best results were as follows:Seed age 18 h,initial pH value 9.0, inoculum size 3%, culture temperature 37℃, Shaking speed 160 r/min, Liquid volume 100 mL/500 mL, culture time 36 h. Under optimal conditions in culture, the number of Bacillus natto had reached 2.13×1010 cfu/mL, increased 71.8% than not optimized.Thirdly, the optimum centrifugal rotational speed and centrifugal time were 6000 r/min and 10 min, the harvest rate was 95.8% for W13. Vacuum freeze-drying was used to preparer DVS Bacillus natto starter.Finaly, cell concentration, material thickness, pH and temperature of the cold shock treatment impact on survival of vacuum freeze-drying been studied. The optimal material thickness was 0.5 cm (corresponding to the sample volume 2 mL); the best pH of samples was 7.0; the best conditions of cold shock treatment:treatment 8 h, under 6℃. Single factor experiments to study cryoprotectant impact on survival of vacuum freeze-drying.Through orthogonal optimization, the best composition cryoprotectant of is as follows 10% skim milk, 10% sucrose,5% maltodextrin,0.5% ascorbic acid. The livablity of vacuum freeze-drying was 85.4%, the cell density of freeze-drying starter was 1.71×1011 cfu/g.The freeze-drying starters was stabilization on cell density of live bacteria and fermentation performance, after conserving 3 months in 4℃and -18℃.