Screening And Identification Of Super Lactic Acid Bacteria From Traditional Fermented Yak Milk And The Antioxidant Properties Of Yogurt

The study used Yak milk powder as raw materials and fifty-six lactobacillus strains as fermentation strain, Screening and Identification of super Lactic Acid Bacteria from Traditional Fermented Yak Milk and the antioxidant properties of fermentation yoghurt. The main research includes:Screening,16S rDNA Homology Analysis and antioxidant properties of super lactic acid bacteria; Combinatorial screening of lactic acid bacteria, selects the best combinations with synergistic effect; Using single-factor test and orthogonal test, parameters that influences the quality of product were analyzed and optimized; The antioxidant properties of fermented yak yogurt; the volatile flavor compounds of fermented yak yoghurt.The main concludes are as follows:1.Screening, Identification and Antioxidant properties of super Lactic acid bacteria:Screening excellent fermentation performance7strains from56strains of lactic acid bacteria strains by first screening and further screening, through the16S rDNA molecular identification, we get the result:TG3-4was Enterococcus durans; TG2-4and KDLL-2were Enterococcus faecium or Enterococcus durans; TG3-2and DLDQ2-1were Lactobacillus casei; TG1-11was Lactobacillus paracasei; TG1-1was Lactobacillus casei or Lactobacillus paracasei.2. The antioxidant properties of super lactic acid bacteria:Analysis the7strains of lactic acid bacteria of antioxidant properties, all samples have strong ability of scavenging DPPH free radical, ABTS free radical, FRAP value, superoxide anion radical and hydroxyl radical, The antioxidant properties of Lactic acid bacteria extracellular secretions were greater than Lactic acid bacteria intracellular extract, the antioxidant ability of TG2-4, TG3-4and DLDQ2-1were strong, there was further research and development value.3. Combinatorial screening of super lactobacilli and optimization of Yak yogurt process: Combined screening of the TG1-1, TG1-11, TH3-4, DLDQ2-lstrains of Lactobacillus, Optimum fermentation combination of strains was determined by combined fennentation experiments. The effects of the ratio of strains fermentation Temperature, inoculation amount, sucrose adding amount on the quality of the products were studied and optimized through the orthogonal test. The optimal technological parameters of fermentation conditions were fixed: the ratio of TG1-1to TG1-11was2:1, inoculation amount6%, fermentation Temperature42℃, sucrose adding amount4%. 4. The antioxidant properties of yoghurt: Analysis the antioxidant properties of yak yoghurt, The result showed that yak yoghurt had strong ability of scavenging DPPH free radical, scavenging ABTS free radical, FRAP value, superoxide anion radical and hydroxyl radical, the scavenging rate of the DPPH free radical was64.54±0.12%, the ABTS free radical was25.99%～85.60%, the FRAP value was10.121±0.034μmol FeSO4/ml, the superoxide anion radical was83.69±0.14%, the hydroxyl radical was54.72±0.12%.5. The analysis of volatile flavor substances:By means of HS-SPME and GC-MS method, the volatile flavor substances in yak yoghurt, was analyzed, The result showed that yak yoghurt had many kinds of different volatile compounds, including Acids, esters, ketones and alcohol and other substances, The main volatile component of yak yogurt were Acetic acid, Myristic acid, Palmitic acid,Methyl stearate and Octadecanoic acid, they formed the unique taste of yogurt.