嗜热链球菌胞外多糖生物合成的研究进展

嗜热链球菌是一种公认的安全性益生菌,作为重要的食品发酵剂,广泛应用在发酵乳和奶酪等食品工业生产中,在发酵过程中起着重要的作用,日益成为食品科学研究的热点之一。由于与其他微生物菌株相比安全性高,目前在医药保健等行业中也有着广泛的应用。在嗜热链球菌代谢产物研究中,胞外多糖(exopolysaccharide,EPS)因独特的理化特性和生理功能而备受研究者青睐。嗜热链球菌来源的EPS不但具有降低胆固醇、抗肿瘤和促进肠道粘附等生理功能,而且还能够作为食品添加剂和稳定剂显著改善食品物性。本文重点介绍了嗜热链球菌EPS的生物合成、EPS合成基因簇及其代谢调控,期望为嗜热链球菌EPS生物合成的深入研究提供参考。     

嗜热链球菌胞外多糖的结构生物合成与遗传调控

介绍了嗜热链球菌胞外多糖的组成结构、生物合成、代谢途径和针对途径中关键酶的遗传调控,为胞外多糖研究提供参考.     

藏灵菇中嗜热链球菌高产胞外多糖发酵条件的优化

利用从藏灵菇中筛选的产胞外多糖(EPS)的嗜热链球菌(Streptococcus thermophilus)研究提高多糖产量的环境因素。针对影响胞外多糖合成的4个因素,采用4因素3水平L9(34)正交试验,确定了高产胞外多糖优化发酵条件,即发酵温度为32℃,发酵时间为16h,培养基起始pH值为6.5,接种量为3%。在此优化条件下,胞外多糖的产量是优化前的2.6倍。     

一株西藏灵菇嗜热链球菌产胞外多糖的流变学特性

以一株西藏灵菇嗜热链球菌为研究对象,系统地研究质量浓度、剪切速率、热处理、pH及盐离子对其所产胞外多糖流变学特性的影响。结果表明,该胞外多糖溶液具有良好的增稠性,质量浓度为8.6 mg/mL时其黏度可达到85.63mPa.s;多糖溶液呈高度假塑性,剪切稀释现象明显;热稳定性差,当温度由20℃升至100℃时,其黏度下降了74.4%,分别于60,80℃热处理150min,对多糖溶液黏度有不同程度的影响;多糖溶液黏度在酸性条件下相对稳定,但在中性和碱性条件下明显升高;并且随Ca2+浓度升高,多糖溶液黏度显著下降。     

一株嗜热链球菌ST1 的产胞外多糖流变学特性

以从天然发酵乳制品中筛选的一株嗜热链球菌ST1 产生的胞外多糖为研究对象,对该胞外多糖的流变学特性进行分析。结果表明：ST1 胞外多糖溶液是典型的非牛顿假塑性流体,溶液流动行为受多糖质量浓度、温度、剪切时间及pH 值的影响;多糖溶液黏度随着质量浓度的升高而增加,多糖溶液质量浓度越高剪切稀释现象越严重;在10～80℃范围内多糖溶液黏度变化很小,有很好的耐温性;在0～900s 剪切时间作用下,溶液黏度一直处于下降趋势;多糖在pH 4 的溶液中黏度相对较稳定,在pH 7 和pH 10 的溶液中随剪切速率的升高黏度下降幅度较大;加入1g/100mL 的多糖能够明显增加脱脂乳的黏度,但随着剪切速率的增高,多糖对脱脂乳黏度的影响变小。     

嗜热链球菌KLDSSM胞外多糖生物合成途径的分析

为了从遗传水平上探究嗜热链球菌KLDS SM合成胞外多糖（EPS）的能力,本研究从糖被转运进入胞内、糖核苷酸合成及EPS基因簇三方面所涉及的基因进行了相关分析。结果发现,该菌能够转运葡萄糖、乳糖、蔗糖、海藻糖及甘露糖5种糖,具有代谢葡萄糖、乳糖、果糖、蔗糖、海藻糖与甘露糖形成糖酵解中间代谢产物的酶类,拥有合成EPS前体物质UDP-葡萄糖、UDP-半乳糖、UDP-N-乙酰基葡糖胺、UDP-呋喃半乳糖与d TDP-鼠李糖的潜力。同时序列比对分析发现该菌具有一个与高产EPS的菌株ASCC 1275一致性极高的EPS基因簇,且EPS初步产量测定约为331 mg/m L,表明该菌是一株高产EPS潜力菌株,具有较大的应用潜能。      

嗜热链球菌噬菌体对酸奶质量的影响

研究嗜热链球菌噬菌体对酸奶直投式发酵剂(direct vat set,DVS)发酵产酸、嗜热链球菌与保加利亚乳杆菌比例、酸奶黏度、口感、后酸化、乳清析出等方面的影响。结果表明：嗜热链球菌噬菌体可影响酸奶发酵剂发酵产酸、明显改变酸奶嗜热链球菌与保加利亚乳杆菌比例,导致产品黏度降低、口感变差、乳清析出及后酸化严重,嗜热链球菌噬菌体对DVS 生产酸奶有着严重的危害。     

Pilot-scale production of exopolysaccharide from Leuconostoc pseudomesenteroides XG5 and its application in set yogurt

Exopolysaccharide from Leuconostoc pseudomesenteroides XG5 (XG5 EPS) is a linear dextran that is built by glucose units via α-1,6 glycosidic bond. The primary objective of this study was to investigate the yield of XG5 EPS and its application in set yogurt. In laboratory scale, the culture conditions of XG5 EPS production were optimized using the L9 (3³) orthogonal test. Here, the optimized yield of XG5 EPS was 26.02 g/L under the conditions of 100 g/L sucrose, initial pH 7.0, 25°C incubation, and 100 rpm for 36 h in a shaking flask. Based on the optimized parameters of laboratory scale, a pilot fed-batch fermentation was performed in a 50-L bioreactor with an adjusted agitation speed of 20 rpm. The XG5 EPS yield reached 40.07 g/L in fed-batch fermentation, which was 54% higher than that achieved in laboratory scale. In addition, XG5 EPS was added into set yogurt to investigate its effect on the stability of set yogurt. Our data demonstrated that the XG5 EPS improved the water-holding capacity, texture profile, and viscosity of set yogurt during cold storage compared with the controls. In particular, addition of 0.5% XG5 EPS increased the structure of 3-dimensional network of set yogurt, which eventually improved the physical stability of the set yogurt. Overall, this study provided new insights for exploring the pilot scale production and application of dextran.     

西藏灵菇中产胞外多糖嗜热链球菌的分离筛选及其发酵性能测定

从西藏灵菇中分离筛选、鉴定高产胞外多糖的乳酸菌菌株,并对其发酵性能和流变学参数进行测试。筛选的9株菌,菌种鉴定结果均为嗜热链球菌,其中菌株KC1、KC2、KC6、KC17产胞外多糖,菌株KC5、KC7、KC15、KC16、KC22不产胞外多糖。产胞外多糖菌株发酵乳发酵性能、黏度和黏附性指标均明显高于不产胞外多糖的嗜热链球菌,进一步证实了嗜热链球菌产生的胞外多糖可以赋予发酵乳良好的质地。     

嗜热链球菌胞外多糖的分离纯化及理化性质研究

以一株从西藏灵菇中分离的高产胞外多糖嗜热链球菌为研究对象,利用IRIE培养基进行发酵培养,通过离心、除蛋白、醇沉、透析等分离手段获得嗜热链球菌胞外多糖,并通过DEAE纤维素52和DEAE Sepharose CL-6B柱进一步分离纯化。高效液相色谱证实该多糖为纯品。差热扫描量热(DSC)研究显示该多糖有两个熔点分别为120.83℃和212.89℃。热重分析(TGA)表明该多糖第一步热分解温度为264.88℃,第二步热分解温度为441.82℃。红外光谱分析揭示该多糖具有较长分子链,有β-糖苷键构型特征。     

嗜热链球菌CH9胞外多糖的分离纯化及结构分析

对嗜热链球菌CH9胞外多糖进行分离纯化,经DEAE-52离子交换柱及Sephadex G-100凝胶柱得到单一组分,利用高效液相色谱(HPLC)测其分子质量,结果表明:EPS1a为中性多糖,分子质量为1.8×106u;EPS2a、EPS3a为酸性多糖,分子质量分别为1.06×106、1.05×106u。经琼脂糖凝胶电泳及Sephadex G-100凝胶柱鉴定3种糖均为单一组分。紫外及红外光谱扫描结果显示:3种糖均具有多糖的特征吸收峰,且EPS2a、EPS3a可能为糖与蛋白的复合物。刚果红实验表明:EPS1a具有三股螺旋结构,而其他两种糖并未发现此现象。β消去实验证明:EPS1a、EPS3a为—O—连接,EPS2a为—N—连接。     

Comparison of the functionality of exopolysaccharides produced in situ or added as bioingredients on yogurt properties

The effect on yogurt properties of in situ production of exopolysaccharides (EPS) and addition of 2 EPS powders (crude and purified EPS from Lactobacillus rhamnosus RW-9595M fermentation in whey-based medium) at different concentrations was studied. No effect of purified powder addition for EPS concentrations up to 500 mg/L was observed on acidification rate to the difference of milks supplemented with crude EPS, which exhibited longer acidification times. The addition of EPS from 125 to 500 mg/L or the use of EPS-producing cultures resulted in yogurts with lower yield stress and viscoelastic moduli compared with control yogurts without EPS, with no apparent effect of EPS concentration. However, the consistency index was higher for yogurts produced with the commercial EPS-producing culture, and to a lesser extent with the mixed culture containing Lb. rhamnosus RW-9595M, compared with yogurts supplemented with EPS powders, which were not different from that for control yogurts. Our study showed that the mode of EPS incorporation in yogurts has a major effect on the rheological properties of the final product.     

氮源对嗜热链球菌胞外多糖表型特征的影响

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IMAU20...     

嗜热链球菌的筛选及其高活性菌粉制备

为获得优良酸奶发酵剂嗜热链球菌菌株,并确定制备高活性菌粉的培养基与保护剂,利用改良TJA培养基,自市售酸奶中分离纯化出6株球菌,经生理生化试验鉴定为嗜热链球菌。进一步对它们的发酵特性进行比较,结果表明ST4发酵性能优良。以10%复原脱脂乳为基础培养基,通过正交试验方法优化得出ST4最佳增殖培养基配方为酵母粉0.5%、番茄汁7.5%、麦芽汁7.5%、乳清粉7.5%,活菌数达到1.72×109cfu/mL。正交试验优化所得ST4的最佳保护剂配方为海藻糖20%、乳糖2.5%、谷氨酸钠5%、甘油0.5%,经冷冻干燥后其活菌数达到1.56×1011cfu/g。     

嗜热链球菌对酸奶发酵的影响及应用前景

嗜热链球菌作为一种益生菌,在发酵酸乳的过程中具有重要作用,并日益成为乳品科学研究的热点。目前在食品、药品等行业中的应用日益广泛。文中介绍了嗜热链球菌的发酵与保健功能特性,并对其开发应用前景进行了展望。     

乳制品中嗜热链球菌的快速检测

利用血清学方法检测乳制品中的嗜热链球菌。首先，通过动物免疫方法制备了小鼠及家兔抗嗜热链球菌(Streptococcus thermophilus)的免疫血清。然后，用此血清经酶联免疫吸附测定法(ELISA法)对乳制品中嗜热链球菌进行检测。用间接ELISA法及双夹心ELISA法对乳制品中的嗜热链球菌进行检测。结果表明，两种方法均可测出乳制品中嗜热链球菌，其最低检测量可达10^7mE^-1。这一结果为乳制品中嗜热链球菌的血清学快速检测提供了参考。     

Biochemistry,genetics, and applications of exopolysaccharide production in Streptococcus thermophilus: a review

Many strains of Streptococcus thermophilus synthesize extracellular polysaccharides. These molecules may be produced as capsules that are tightly associated with the cell, or they may be liberated into the medium as a loose slime (i.e., "ropy" polysaccharide). Although the presence of exopolysaccharide does not confer any obvious advantage to growth or survival of S. thermophilus in milk, in situ production by this species or other dairy lactic acid bacteria typically imparts a desirable "ropy" or viscous texture to fermented milk products. Recent work has also shown that exopolysaccharide-producing S. thermophilus can enhance the functional properties of Mozzarella cheese, but they are not phage-proof. As our understanding of the genetics, physiology, and functionality of bacterial exopolysaccharides continues to improve, novel applications for polysaccharides and polysaccharide-producing cultures are likely to emerge inside and outside the dairy industry. This article provides an overview of biochemistry, genetics, and applications of exopolysaccharide production in S. thermophilus.     

保加利亚乳杆菌和嗜热链球菌相互作用的研究

探讨了嗜热链球菌和保加利亚乳杆菌之间的相互作用(拮抗和共生效果)，指出这两个菌种的许多菌株在代谢过程中会产生过氧化氢、细菌素等抑菌性物质，导致嗜热链球菌与保加利亚乳杆菌间表现出非协同生长的现象。在此基础上，建立了评价发酵剂之间相互作用的新的指标体系，旨在方便优良酸奶发酵剂菌种的筛选工作。     

嗜热链球菌噬菌体的分离纯化与鉴定

噬菌体颗粒的分离纯化是研究噬菌体生物学特性、基因分析的基础工作。本研究采用聚乙二醇浓缩噬菌体增殖液、缓冲液透析去除聚乙二醇、氯化铯密度梯度离心纯化,得到了纯度较高的嗜热链球菌噬菌体样品。多重PCR鉴定和SDS-PAGE蛋白组成分析结果表明,该嗜热链球菌噬菌体的包装机制为pac-型。      

嗜热链球菌CRISPR序列的检测及原间隔序列预测

CRISPR基因座中的间隔序列能够提供特异性免疫使宿主得以对抗那些携带相同序列的入侵元件,本研究旨在预测实验室3株嗜热链球菌的原间隔序列,为探究其抗噬菌体机制奠定基础。本文检测了3株嗜热链球菌的CRISPR序列,预测嗜热链球菌CRISPR基因座的活性,构建重复序列的系统发育树,并对间隔序列进行同源性分析。结果显示供试菌S0含有3个CRISPR,S4仅含1个CRISPR,79含有4个CRISPR,CRISPR1基因座活性最高,CRISPR2基因座最不活跃。重复序列与标准菌株的相应重复序列高度保守,不同CRISPR的间隔序列在内容及数目上高度可变,它们的原间隔序列绝大部分来源于噬菌体,少数来源于质粒或染色体序列。供试菌79与嗜热链球菌MN-BM-A02及嗜热链球菌ASCC 1275的4个CRISPR序列均高度一致,推测其菌株同源性较高。验证了间隔序列是由宿主遭受噬菌体等外源基因元件侵染而获得的。