关键词: 胞外多糖, 流变特性, 激光光散射, 酸性乳饮料

Abstract: The present study was carried out to optimize the fermentation conditions for exopolysaccharide (EPS) production by Bacillus amyloliquefaciens GSBa-1, isolated and screened from the traditional rice wine starter. The optimal fermentation conditions obtained by single factor experiments and response surface analysis were as follows: the culture medium consisted of peptone 10 g/L, yeast extract powder 5 g/L, sucrose 40 g/L, and NaCl 10 g/L and the fermentation was performed for 36 h at 35 ℃ with an inoculum size of 4% at a shaking speed of 160 r/min. The maximal production of EPS of 326.45 mg/L was obtained under the above conditions. The results of rheological studies indicated that the aqueous solution of the EPS had low viscosity, which increased with increasing its concentration and shearing rate. Measurement of molecular parameters by multi-angle laser light scattering showed that the weight-average molecular mass (mw) of the EPS was 4.993 × 105 g/mol, the radius of gyration (Rg) 48.34 nm, hydrodynamic radius (Rh) 64.62 nm, and Rg/Rh ratio (ρ) 0.748, indicating that the EPS molecule may be present as compact spheres. This was also confirmed by transmission electron microscope. The application of this EPS in acid milk beverage showed that the use of the EPS could improve the stability of the beverage without increasing its viscosity, indicating that the EPS from Bacillus amyloliquefaciens GSBa-1 can be potentially used as a novel food stabilizer.

Key words: exopolysaccharide, rheological characterization, laser light scattering, acid milk beverage