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This test collected from the Gannan Tibetan Autonomous Prefecture, Gansu Province (cooperation that pull on behalf of the village, my village, the Xiahe County Bora Township bar wine village, color, Colorado Village and Xiahe County Amu to go almost the Township Xiliningba Ga plus Kimura, China Malong village 40) herders homemade 10 acid yak milk as the research object, using than nephelometry lactic acid titration GB method, spectrometry, rotation method, the paper method of which isolated 86 strains of lactic acid bacteria (including Bacillus 46 cocci ), the preferred screening, rescreening test as well as a combination of fermentation tests to determine the best fermented yogurt bacteria, bacteria composition and fermentation conditions. The results are as follows: 1. Screening: genetic stability, coagulation time, the Acidity and sensory characteristics, the eight the curd-time 3 6 h fermentation acidity in 62 1 03 o T, curd good state and having good sensory lactobacillus strain, wherein Bacillus 4 (B-3-7, B-4-1, E-4-3 , F-2-1), 4 cocci (A-2-1, D-7-1, H5, J7,). Rescreening: (1) growth performance: growth curves of eight lactic acid bacterial strains in liquid medium and milk, that bacilli in liquid medium for 12 hours, cocci 10h end of the logarithmic growth phase; preparation fermentation agent Bacillus 10h, the cocci 8h quickly harvest available ideal fermentation agent quality. (2) fermentation performance: eight lactic acid bacteria fermented yogurt acidity after acidification of capacity, acetaldehyde and diacetyl content, viscosity, lactobacillus viable count: 4 bacilli acid production capacity than four cocci T the acidity range 60 o 12 o T; refrigeration process, cocci showed good anti the acidification ability to (post-acidification weak ), D-7-1 during cold storage acidity increased by only 8 o T, stable quality of preservation period; B-3-7-fermented yogurt strains producing ability of flavoring substances higher acetaldehyde content 32.16μg/mL F-2-1 followed by smaller 28.35μg/mL eight strains of lactic acid bacteria producing diacetyl content in 0.61 1 .15μg/mL, between Very good; from the product sticky nature, D-7-1 showed a very good viscosity characteristics, the average viscosity of 5.72 × 10 3 mpa.s, this highly viscous strains for the production of yogurt with the state; 8 of lactic acid bacteria fermented yogurt at 4 ℃ 20d can keep lactic acid bacteria number of viable cells in 10 7 cfu / mL. (3) resistance to adverse environmental performance: 8 of lactic acid bacteria acid, bile salts and osmotic pressure showed tolerated. Under acidic conditions of the limit pH1.5, F-2-1 could grow, showing a low pH tolerate endurance; When cholic salt concentration reached 0.5% of D-7-1, A-2-1 E-4-3 and F-2-1 could grow, to show the ability to better tolerate high bile salt; strains F-2-1, E-4-3 and D-7-1, the concentration of up to 8% NaCl showed a certain degree of tolerance. (4) the strongest antimicrobial activity: Staphylococcus aureus inhibition of E-4-3 inhibition zone diameter of 21mm, the effect of suppressing the strain B-3-7 after E-4-3 is 20mm; inhibition for E. coli, J7 and F-2-1 effect stronger inhibition zone diameter of 18mm; inhibition of Bacillus subtilis F-2-1 inhibition zone diameter 22mm, suppression bacterial effect. 3. Combination of fermentation: research synergies between 8 strains, sensory evaluation and physical and chemical indicators screening to the the best fermentation combination D4: (E-4-3 and D-1). By L 9 (3 4 ) the orthogonal experimental combination of strains fermentation process parameters: bacteria ratio of 1:1, inoculum size 3%, fermentation temperature 42 ° C, The sweetened amount 6%. Combination of fermentation compared with the single-fermentation, the combination of fermented the yogurt curd-time only 3h10min, acidity up to of 110.21 o T, refrigerated 20d acidity only increased 7oT of the final product viscosity up to 5.68 × 10 3 mpa.s, acetaldehyde content 30.36μg/mL, and diacetyl 0.85μg/mL, 4 ℃ refrigeration 20d Lactobacillus number of viable cells maintained in 10 9 cfu / mL or more. In summary, the eight lactic acid bacteria isolated acid yak milk production of the test from the Tibetan Herdsmen strengths, obtained better results in the screening, rescreening and combination of fermentation process. Of fermented dairy products used in the study, use and development of lactic acid bacteria has a positive meaning, at the same time for homemade DVS fermentation agent, reduce production costs and improve the economic efficiency of enterprises, etc. This is not only to provide relevant scientific basis.
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