title: Structural characterization of the exopolysaccharide produced by Streptococcus thermophilus 05-34 and its in situ application in yogurt.
abstract: An exopolysaccharide (EPS) producing strain was isolated from Tibetan kefir grains in China, which was identified by 16S rDNA tests and designated as Streptococcus thermophilus 05-34. The high-performance liquid chromatography analysis showed that it was composed of galactose and glucose in a molar ratio of 1.0:0.8 with a molecular mass of 2.5 × 10(4)  Da. EPS was further revealed to have α-d-glucose, α-d-galactose, β-d-glucose, and β-d-galactose by Fourier transform infrared spectroscopy combined with 1D (1) H nuclear magnetic resonance spectroscopy. The length of EPS ranged from 10 to 100 nm and the maximal height of lumps was 2.5 nm through atomic force micrograph analysis. Furthermore, yogurt fermented with EPS-producing S. thermophilus 05-34 exhibited lower susceptibility to whey separation, higher viscosity, and sensory scores than those made with non-EPS-producing strain in yogurt production. These results suggested that EPS-producing Streptococcus thermophilus 05-34 provided a potential application in the fermented dairy industry.
authors.affiliation: Key Laboratory of Functional Dairy of Ministry of Education of the People's Republic of China and Municipal Government of Beijing, College of Food Science and Nutritional Engineering, China Agricultural Univ., 17 Qing Hua East Road, Hai Dian District, Beijing 100083, China.
authors.forename: Q Q
authors.initials: QQ
authors.lastname: Qin
authors.forename: B S
authors.initials: BS
authors.lastname: Xia
authors.forename: Y
authors.initials: Y
authors.lastname: Xiong
authors.forename: S X
authors.initials: SX
authors.lastname: Zhang
authors.forename: Y B
authors.initials: YB
authors.lastname: Luo
authors.forename: Y L
authors.initials: YL
authors.lastname: Hao
mesh_terms: D002681:China; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D043302:Cultured Milk Products / Q000382:microbiology*; D005285:Fermentation; D005690:Galactose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008970:Molecular Weight; D011135:Polysaccharides, Bacterial / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D048249:Streptococcus thermophilus / Q000378:metabolism*; D015014:Yogurt / Q000382:microbiology*
chemical_list: D011135:Polysaccharides, Bacterial; C098632:exopolysaccharide, Streptococcus; D005947:Glucose; D005690:Galactose