The Characteristics and Fermentation Performance of Lactic Acid Bacteria with High Extracellular Polysaccharide Production from Traditional Yak Yogurt

In order to study the characteristics and fermentation performance of high-yielding extracellular polysaccharide lactic acid bacteria in traditional yak yoghurt from Tibetan areas in Sichuan, six strains of high-yielding extracellular polysaccharide lactic acid bacteria isolated in our laboratory were taken as the research object, and the characteristics of strain growth, acid tolerance, bile salt tolerance, osmotic pressure tolerance and cell surface hydrophobicity were studied as the indexes. The fermentation performance of fermented yoghurt was studied with the indexes of coagulating time, water retention, acidification and post-acidification capacity, volatile substances and texture. The growth curve showed that the six strains entered the logarithmic growth stable stage at 14 h (218, 276, 266) and 16 h (271, 285, 231), respectively. Among them, the strain numbered 218 had the highest growth with OD value of 2.188. The results of tolerance test showed that strain 276 had good ability to tolerate acidity (P<0.05). Strains 266, 218 and 231 had strong bile salt resistance. All the six strains had good osmotic pressure tolerance, among which strain 285 had strong osmotic pressure tolerance. The hydrophobicity of strains 285 and 218 in the two organic reagents was significantly (P<0.05) higher than that of the other strains, and the binding effect with cetane was better. The results of fermentation test showed that the fermented yogurt of 6 strains coagulated within 6 h to 8 h, and the number of viable bacteria remained above 10⁷ CFU/mL during the cold storage, which met the standard of starter culture. The highest value of strain 276 was 3.22×10⁶ CFU/mL. The yoghurt produced by strain 218 had better texture characteristics, and its water holding capacity and acidification capacity were 60.98% and 83 °T, respectively, compared with those of the other strains. Strains 276 and 266 had better post-acidification resistance. Strain231 had the best aroma-producing property, with acetaldehyde content of 24~26 μg/mL and diacetyl content of 1.58~2.51 μg/mL, which could significantly improve the flavor of yoghurt. Through comprehensive comparison of the characteristics and fermentation performance of six strains of lactic acid bacteria with high extracellular polysaccharide yield, strain 218 was a strain with good performance and good stability, which can be used as a fermentation agent of lactic acid bacteria with certain application potential. This study provides a theoretical basis for the application of lactic acid bacteria with high extracellular polysaccharide yield isolated from traditional yak yoghurt in Tibetan area of Sichuan in the fermentation of dairy products.