氮源对嗜热链球菌胞外多糖表型特征的影响

Effects of Nitrogen Sources on the Phenotypic Characteristics of Exopolysaccharide from Streptococcus thermophilus

乳酸菌胞外多糖(EPS)具有增加发酵乳黏度,防止乳清析出,增强凝乳强度等特性,是目前食品科学领域的研究热点之一。本研究以基础培养基M17为对照,以大豆蛋白胨、胰蛋白胨和酪蛋白胨替代M17液体培养基的复合氮源,探究不同氮源对嗜热链球菌IMAU20561胞外多糖的产量、分子质量及结构的影响。结果表明:嗜热链球菌IMAU20539以大豆蛋白胨为唯一氮源的M17培养基中胞外多糖产量达480.7 mg/L,远高于其它3种培养基所得多糖的产量。不同氮源培养基所得粗EPS经纯化后收集的EPS组分不同,各EPS组分的分子质量也有显著差异,以酪蛋白胨为唯一氮源的M17培养基所得EPS分子质量最大(5.964×105u),其次为基础培养基M17(1.260×105u)、大豆蛋白胨培养基(6.635×104u)和胰蛋白胨培养基(1.192×104u)。不同氮源培养基所得多糖结构有显著差异,大豆蛋白胨培养基所得EPS主要由半乳糖醛酸、半乳糖和阿拉伯糖组成;胰蛋白胨培养基所得EPS主要由葡萄糖醛酸、葡萄糖和半乳糖组成;酪蛋白胨培养基和基础培养基M17所得EPS有相似的单糖组成,主要由甘露糖、葡萄糖和半乳糖组成,占比分别为10.46∶1.62∶87.37和20.37∶2.77∶74.91。

Lactic acid bacteria exopolysaccharides have the characteristics of increasing the viscosity of fermented milk,preventing the precipitation of whey,and enhancing the strength of curd.It is currently one of the research hotspots in the field of food science.In this study,the basic medium M17 was used as a control,and the compound nitrogen source of M17 liquid medium was replaced with soy peptone,tryptone and casein peptone to explore the effect of different nitrogen sources on the yield,molecular weight and structure of the extracellular polysaccharide of Streptococcus thermophilus IMAU20561.The results showed that the yield of extracellular polysaccharide in M17 medium with soy peptone as the sole nitrogen source for Streptococcus thermophilus IMAU20539 reached 480.7 mg/L,which was much higher than the yield of polysaccharides obtained from the other three mediums.Among them,the M17 medium with soy peptone as the sole nitrogen source had the highest production of extracellular polysaccharides,reaching 480.7 mg/L.Much higher than the yield of polysaccharides from the other three media.The EPS fractions of the crude EPS obtained from different nitrogen sources were different after purification,and the molecular weight of each EPS fraction was also significantly different.The M17 medium with casein peptone as the sole nitrogen source had the highest EPS(5.964×105 u),followed by basic medium M17(1.260×105 u),soybean peptone medium(6.635×104 u) and tryptone medium(1.192×104 u).There were significant differences in the structure of polysaccharides obtained from different nitrogen sources.The EPS obtained from soy peptone medium is mainly composed of galacturonic acid,galactose and arabinose;the EPS obtained from the tryptone medium mainly consists of glucuronic acid,glucose and galactose.The EPS obtained from casein peptone medium and basic medium M17 had similar monosaccharide composition,mainly composed of mannose,glucose and galactose,and the percentages were 10.46 ∶ 1.62 ∶ 87.37 and 20.37 ∶ 2.77 ∶ 74.91,respectively.