The pH value was essential for the growth and metabolism of microorganisms. Acidic pH exopolysaccharide (AC-EPS) and alkaline pH exopolysaccharide (AL-EPS) secreted by A. australica QD mediated by pH were studied in this paper. The total carbohydrate content and molecular weight of AC-EPS (79.59% ± 2.24% (w/w), 8.374 × 10⁵ Da) and AL-EPS (82.48% ± 1.46% (w/w), 6.182 × 10⁵ Da) were estimated and compared. In AC-EPS, mannose (3.78%) and galactose (3.24%) content was more, while the proportion of glucuronic acid was less in comparison to AL-EPS. The scanning electron microscopy revealed the structural differences among the AC-EPS and AL-EPS. Thermogravimetric analysis showed degradation temperatures of 272.8 °C and 244.9 °C for AC-EPS and AL-EPS, respectively. AC-EPS was found to exhibit better rheological properties and emulsifying capabilities, while AL-EPS had superior antioxidant activities. Overall, both AC-EPS and AL-EPS have the potential to be used as emulsifiers and biological antioxidants.

Graphical Abstract

中文翻译：

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发酵pH对澳大利亚交替单胞菌QD胞外多糖结构、流变学性质和抗氧化活性的影响

pH值对微生物的生长和代谢至关重要。本文研究了由 pH 介导的A. australica QD分泌的酸性 pH 胞外多糖 (AC-EPS) 和碱性 pH 胞外多糖 (AL-EPS) 。^{AC-EPS (79.59% ± 2.24% (w/w), 8.374 × 10 5}  Da) 和 AL-EPS (82.48% ± 1.46% (w/w), 6.182 × 10 ⁵ )的总碳水化合物含量和分子量 Da）进行了估计和比较。与AL-EPS相比，AC-EPS中甘露糖(3.78%)和半乳糖(3.24%)含量较多，而葡萄糖醛酸所占比例较少。扫描电子显微镜揭示了 AC-EPS 和 AL-EPS 之间的结构差异。热重分析显示 AC-EPS 和 AL-EPS 的降解温度分别为 272.8 °C 和 244.9 °C。发现 AC-EPS 表现出更好的流变性能和乳化能力，而 AL-EPS 具有更好的抗氧化活性。总体而言，AC-EPS 和 AL-EPS 都具有用作乳化剂和生物抗氧化剂的潜力。

图形概要