嗜热链球菌MGB80-7所产胞外多糖的表型结构及其抗氧化活性

Phenotypic structure and antioxidant activity of exopolysaccharide produced by Streptococcus thermophilus MGB80-7

摘要:

【背景】胞外多糖(exopolysaccharide，EPS)是乳酸菌生长代谢过程中所产生的一种次级代谢产物，除了可以改善产品质构和品质外，其生理功能也是近年来研究人员追捧的热点。【目的】探究乳酸菌EPS的表征特性和分子结构，揭示其与EPS益生特性之间的联系。【方法】以产EPS的嗜热链球菌(Streptococcus thermophilus，S. thermophilus) MGB80-7为研究对象，利用苯酚-硫酸法测定菌株EPS产量。采用离子交换柱层析和凝胶分子筛层析对该菌株所产EPS进行分离纯化，结合凝胶色谱、红外光谱及高效液相色谱对EPS表型结构进行剖析。此外，为确定EPS表型特征对其抗氧化活性的影响，测定了EPS对超氧阴离子、羟自由基及DPPH自由基等的清除能力。【结果】S. thermophilus MGB80-7在M17培养基中EPS产量较高，为(268.25±5.36) mg/mL，分离纯化后共得到2种多糖组分，其中中性多糖(WPS-807)分子量为1.028×10⁵ Da，主要由葡萄糖、半乳糖和甘露糖组成，并含有少量的鼠李糖和阿拉伯糖，酸性多糖(SPS-807)分子量为8.601×10⁴ Da，单糖组分相较于WPS-807更为复杂，主要由甘露糖、半乳糖和阿拉伯糖组成。抗氧化活性的结果表明，EPS-807具有一定的抗氧化活性，尤其对羟自由基的清除能力较好。【结论】S. thermophilus MGB80-7所产EPS的分子量、结构特征对其抗氧化活性具有一定影响，此结果为进一步分析乳酸菌EPS的构效关系和抗氧化机制提供基础。

Abstract:

[Background] Exopolysaccharide (EPS) is a secondary metabolite produced during the growth and metabolism of lactic acid bacteria. In addition to improving the texture and quality of products, its physiological function has also attracted the interest of scholars in recent years. [Objective] This study intends to explore the characterization and molecular structure of EPS of lactic acid bacteria, and to reveal the relationship between it and the probiotic properties of EPS. [Methods] The EPS produced by Streptococcus thermophilus MGB80-7 was studied. To be specific, the yield of EPS was determined with the phenol-sulfuric acid method. Then the EPS was separated and purified by ion exchange column chromatography and gel molecular sieve chromatography, and the phenotypic structure of EPS was analyzed based on gel chromatography, infrared spectroscopy, and high performance liquid chromatography. As for the antioxidant activity, the ability to scavenge superoxide anion, hydroxyl radical, and DPPH radical was detected. [Results] The EPS yield of MGB80-7 in M17 medium was high, which was (268.25±5.36) mg/mL. After separation and purification, two components were obtained. Among them, the neutral polysaccharide (WPS-807, 1.028×10⁵ Da) was composed of glucose, galactose, and mannose, and a small amount of rhamnose and arabinose, and the acidic polysaccharide (SPS-807, 8.601×10⁴ Da) was made up of complex monosaccharides, which was dominated by mannose, galactose, and arabinose. EPS-807 can scavenge some free radicals, especially the hydroxyl radicals. [Conclusion] The molecular weight and structure of EPS produced by MGB80-7 influence its antioxidant activity. This result lays a basis for further analysis of the structure-activity relationship and antioxidant mechanism of EPS from lactic acid bacteria.