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Exopolysaccharide produced by Streptococcus thermophiles S-3: Molecular, partial structural and rheological
Zhiyuan Xu1, Qingbin Guo2, Hui Zhang3
1Shanghai Engineering Research Center of Food Microbiology, School of Medical Instrument and Food Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China; State Key Laboratory of Dairy Biotechnology, Technology Center Bright Dairy & Food Co., Ltd, Shanghai 200436, China.
Abstract:
Yogurt fermented by Streptococcus thermophiles S-3 strain showed higher viscosity and thicker mouth feel than the ones using other lactic acid bacteria strains, which was due to the higher yield of exopolysaccharide (EPS-3) produced during fermentation process. In the present study, molecular characteristics, partial structural features and rheological properties of EPS-3 were studied using triple-detector HPSEC, NMR and steady & dynamic rheological testing, respectively. EPS-3 showed relatively high molecular weight (574 kDa) and narrow polydispersity Index (1.27). Monosaccharides composition analysis indicated that EPS-3 was composed of N-Acetyl-galactosamine, galactose and glucose in the molar ratio of 1:2:1. Conformational parameters from Mark-Houwink equation (0.68) and Rg & Mw relationships (0.56) both indicated a random coil conformation of EPS-3. Results from steady flow tests showed an obvious shear thinning behavior, which was enhanced with the increased concentrations and decreased temperatures. Dynamic rheology indicated that EPS-3 was reluctant to form gel in water solution (G" > G'). EPS-3 demonstrated compatible interaction with milk protein with less syneresis in comparison to the yogurts adding agar and/or pectin. With all the information provided, this study could help promote the application of both EPS-3 and S. thermophiles S-3 strain in different dairy products.
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