Fermentation Characters Of Lactobacilli Delbrueckii Subsp.Bulgaricus And Optimization Of Culture Congitions

Yogurt industrial production is in the rapid development of stage in China. And foreign companies had completed the commercial production of high-activity lactic acid bacteria direct-vat-strain, and monopolized the foreign and domestic market at present. Some questions we faced to during yogurt starter cultures industry were isolated, identified and selected strains with good fermentation characteristics, the optimizing fermentation conditions and industrial media were also confirmed by the optimization design, the appropriate concentration and separation conditions and control parameters were obtained in order to harvest bacterial cells, high-density proliferation was achieved by using aerobic respiration at the same time, and the efficient freeze-drying protective agent were also confirmed by the optimization design. Lactobacillus delbrueckii subsp. ulgaricus as one of the more important strains must be fast acid-producing, good flavor and high viable count, at the same time they were suitable for the production of high-quality yogurt. According to the existing problems in the yogurt starter cultures industry, this project focused on the following areas:Firstly, Lactobacillus delbrueckii subsp. ulgaricus strains with good fermentation characteristics were identified and selected from all of them were researched more in the KLDS. Secondly, the optimizing fermentation media were confirmed by the optimization design. In order to lay a foundation for the development of yogurt DVS starter cultures.Four experimental strains were identified by using16S rRNA gene sequence analysis, and they were Lactobacillus delbrueckii subsp. ulgaricus. And two strains of them with excellent fermentation characteristics were screened successfully by analysising four experimental strains’ fermentation characteristics including acid-producing ability, postacidification property, texture and sensory quality of the yogurt which were fermented by single strain or combination with Streptococcus thermophilus strains. There are strain L7and strain L15which were suitable for the production of yogurt starter cultures.The experiment indicated that the viable cells of strain L7after being cultivated for12h in the optimized medium.Using the path of steepest aseent experiments and RSM method Box-Behnken design, the quadratic regression fitting was carried out by Design Expert software, the quadratic polynomial regression equation of the WHEY POWDER, yeast extract, and calcium carbonate was:Y=178.80+16.63A+0.13B+14.75C-0.50AB-5.75AC+11.75BC-61.40A2-19.90B2-22.15C2The Similar experiment indicated that the viable cells of strain L15was at18h in the medium consisting of6percent enzymatic hydrolysis skim milk, whey powder, yeast extracts and calcium. And the quadratic polynomial regression equation was:Y=350.60+22.13A+19.25B+8.88C-7.75AB-2.00AC+23.25BC-27.55A2-32.80B2-27.05C2The cell count of strain L(?) can reach to1.55×109CFU per milliliter in growing medium consisting of6percent skim milk by enzymatic hydrolysis,49.14gram per liter whey powder,6.63gram per liter yeast extracts and6.63gram per liter calcium, After being cultivated for12h in the3liter growing medium under the temperature42℃, stirring speed80r/min, constant pH=5.8. At the same controlled conditions,adding58.21gram per liter whey powder,10.44gram per liter yeast extracts and2.43gram per liter calcium to6percent enzymatic hydrolysis skim milk,the experimental strain L15biomass were significantly increased to3.24×109CFU per milliliter at18h. The level of innovation indicated that this DVS yogurt starter cultures had high viable count and high activity, and reached the foreign level of starter cultures.