摘要：We aimed to determine the effect of Luria-Bertani (LB) medium, nutrient broth (NB) and tryptic soy broth (TSB), pH, temperature, and incubation time on the production of extracellular polysaccharides (EPS). The effect of glucose, whey and glycerol on bacterial EPS production by Bacillus pseudomycoides U10 was also tested. LB was better than NB and TSB for EPS production. Maximum EPS production was obtained when 1 g/L whey was added to the growth medium. The influence of incubation times (24–96 h), different pH values (6.5, 7.0, 7.5, 8.0 and 9.0) and temperature (25, 30, 37 and 45 °C) were also tested. The optimum pH level was 7.0 and the highest EPS production was observed at 37 °C after 60 h of incubation. Glycerol was not a good carbon source for cell growth and EPS production. The difference in carbohydrate and protein amount was related to the different types of EPS (dissolved and particulate). In general, the uronic acid content in particulate EPS was lower than in dissolved EPS. The maximum uronic acid was obtained from dissolved EPS (16 mg uronic acid/g EPS). According to X-ray diffraction (XRD), thermogravimetric EPS have a poorly crystalline nature and exhibit two-step degradations, corresponding to the weight loss of moisture and/or carboxyl group and the pyrolysis of EPS, without distinctive changes in different media conditions. Small-angle X-ray scattering (SAXS) data indicate the layer thickness of the bacterial EPS is from 12.04 to 14.07 Å for whey and dissolved LB conditions, respectively. It was found that EPS structures changed with whey addition, such as higher d-values, lower weight losses and more filamentous structures which seemed to be related to increasing durability and/or stability.
