Study On Prope(?)ties Of High Exopolysacchride-Producing Strec(?)cus Thermophillus

The optimal fermentation conditions and probiotic characteristics of high exopolysacchride-producing Streotococcus thermophillus isolated from Tibetan Saussurea were studied. Meanwhile, this study comfirmed the optimal fermentation conditions of Streptococcus thermophilus mixed culture with Lactobacillus bulgaricus and Lactobacillus acidophilus and analyzed the properties during the process of fermented and storing.In addition, the paper had a preliminary research on the rheological properties. The results will have some guildences on the improvement of microstructure of yoghurt and the development of efficient DVS Yogurt.The results indicate that the appropriate solid substrat is improved IRIE. The optimal fermented conditions were determined by L9(34) orthogonal experiments. the optimal fermentation conditions with Streotococcus thermophillus were pH6.8,42℃,inoculation size3%(v/v).Streotococcus thermophillus has strong tolerance ability to low pH and high bile salt concentrations, the viable count of S.t. could reach above106cfu/mL after4h fermentation under the condition of pHl.5-4.5and0.05%～0.35%bile salt;The antibacterial activities to the pathogenic Escherichia coli. and Staphylococcus aureus were obvious. It can be used as microecological preparation and yoghurt starter.The optimal fermented conditions were determined by L9(34) orthogonal experiments with comprehensive evaluation of multiple mark.The optimal fermentation conditions with mixed cultivation are:42℃, inoculation size4%(v/v), the strains matching ratio of high exopolysaccharides-producing Streptococcus thermophilus, Lactobacillus bulgaricus and Lactobacillus acidophilus is3:2:1according to acidity, content of acetaldehyde and viscosity.On the optimal fermented conditions, mixed cultivation of lactic acid bacteria significantly improve viable count,acidity,acetaldehyde content,diacetyl content,viscosity, exopolysaccharide(EPS),water holding capacity,the activity of P-galactosidase and protease(P <0.01). The correlative modulus of EPS and viscosity, the activity of β-galactosidase and acidity, the activity of protease and acidity, the activity of protease and acetaldehyde content,viable count and acidity, viable count and acetaldehyde content, EPS and syneresis, EPS and water holding capacity, viscosity and syneresis, viscosity and water holding capacity is high during the fermented process.During the storage process, mixed cultivation of lactic acid bacteria has better post acidification, the viable count could reach above106cfu/mL.viable count. Acetaldehyde content, diacetyl content,viscosity,EPS, water holding capacity, the activity of β-galactosidase and protease kept rising in the first time and then dropping. There were positive correlation between viable count and acetaldehyde content,EPS and viscosity, the activity of protease and acetaldehyde content. There were negative correlation between (3-galactosidase and acidity.The rheological properties of mixed cultivation showed that the viscosity decreased during rotor running up and increased in the process of speed down,it had small thixotropic loop. the mixed cultivation of lactic acid bacteria was a kind of positive thixotropic liquid. The size of thixotropic loop had an important influence on taste.