Abstract

This study aimed to investigate the optimal fermentation condition, purification and rheological properties of extracellular polymers produced by Bacillus subtilis 1006-3. An optimum temperature of 30.2 °C, inoculation amount of 6.1%, and pH of 8.2 were determined via Response Surface Methodology. The result of amino acid analysis and gel electrophoresis indicated that the obtained polymer contained only glutamic acid, with a wide molecular weight range. This polymer was finally determined as γ-PGA by infrared spectroscopy. The γ-PGA solution displayed a behavior of pseudoplastic non-Newtonian fluid with shear thinning properties, which can be described by the Ostward-de Waele power law model. The apparent viscosity of γ-PGA solution increased with the increase in its concentration from 1% to 10%. The deviation in pH from neutral value, and the addition of NaCl or MgCl₂ can reduce the apparent viscosity of γ-PGA solution, and it was more sensitive to Mg²⁺ than to Na⁺ addition. At the concentration of 4, 6, and 8%, γ-PGA solution showed predominantly viscous response in the range of 0.1–100 rad/s angular frequency (G″>G′). These results indicated the potential application of the γ-PGA as a thickening agent.

摘要

本研究旨在探讨枯草芽孢杆菌产生的胞外聚合物的最佳发酵条件、纯化和流变特性。1006-3。通过响应面法确定最适温度为 30.2 °C，接种量为 6.1%，pH 为 8.2。氨基酸分析和凝胶电泳结果表明，所得聚合物仅含有谷氨酸，分子量范围较宽。该聚合物最终通过红外光谱确定为γ-PGA。γ-PGA 溶液表现出具有剪切稀化特性的假塑性非牛顿流体行为，可以用 Ostward-de Waele 幂律模型来描述。γ-PGA溶液的表观粘度随着其浓度从1%增加到10%而增加。pH值偏离中性值，加入NaCl或MgCl ₂可降低γ-PGA溶液的表观粘度，对Mg ^{2+更为敏感}比Na ⁺添加。在 4%、6% 和 8% 的浓度下，γ-PGA 溶液在 0.1-100 rad/s 角频率 ( G ″> G′ ) 范围内主要表现出粘性响应。这些结果表明 γ-PGA 作为增稠剂的潜在应用。