乳酸菌胞外多糖研究新进展

综述了产EPS乳酸菌的筛选方法、已报道的EPS化学结构、分离纯化和结构鉴定的方法、EPS的生理功能、EPS的生物合成及EPS的遗传学和调控方面的研究进展.     

乳酸菌胞外多糖研究进展以及在食品工业中的应用

胞外多糖(exopolysaccharides,EPS)是乳酸菌的一种代谢产物,分为同聚多糖和杂聚多糖。在食品工业中常被用作增稠剂、稳定剂以及乳化剂。近年来,EPS因其抗氧化、抗肿瘤、抑菌等活性引起了人们越来越多的关注。文中从EPS的类型与结构、影响EPS产量的条件、EPS的鉴定及提取方法、EPS的生物活性以及在食品工业中EPS的应用对其进行综述。     

乳酸菌胞外多糖的研究进展

本文总结了菌种、培养基成分、温度、pH值、发酵时间等因素对乳酸菌EPS产量的影响;探讨了提高乳酸菌EPS的生物合成量的方法,旨在加深乳酸菌EPS的研究和推动其应用.     

高产EPS乳杆菌对半脂切达干酪质地改善的研究

通过对高产EPS干酪乳杆菌(EPS++)、不同添加量的半脂切达干酪进行感官评价及对蛋白分解两方面综合分析,确定了EPS++菌株作为辅助发酵剂的最佳添加量为2%(体积分数),并将EPS+和EPS-菌株以此添加量制作对照组干酪进行研究,探讨了高产EPS菌株对半脂干酪组成成分、质构、熔化特性及感官特性的影响。结果表明,EPS++菌株对半脂干酪的质地、熔化性及感官特性均有明显改善,接近全脂对照组切达干酪。     

胶质芽孢杆菌胞外多糖的制备及流变学特性

以实验室保藏的胶质芽孢杆菌SM-01为研究对象,研究了其胞外多糖(EPS)在5 L发酵罐中的发酵过程及制备方法,并对EPS溶液的流变学特性进行了研究,主要分析了质量浓度、剪切速率、剪切时间、温度、pH、无机盐、外加多糖等对其黏度的影响。结果表明,发酵液中EPS的最大产量为23.46 g/L,经离心、醇沉、冷冻干燥后EPS的回收率为76.7%;EPS溶液是典型的非牛顿流体;溶液黏度随着质量浓度的增加而快速增大;25～100℃范围内EPS黏度变化不大;EPS溶液黏度受pH影响较大,其黏度值在pH 7时达到最大,pH>12时溶液成弱凝胶状;加入NaCl、KCl、MgCl2、CaCl2等无机盐后溶液黏度显著下降,Fe3+、Pb2+等高价阳离子使EPS沉淀;EPS与海藻酸钠、黄原胶、瓜尔胶、槐豆胶、阿拉伯胶均有协效性。     

商用车辆电动助力转向系统仿真研究

介绍了商用车辆EPS主要零部件的选定,确定了EPS助力特性,建立了EPS模型,研究了助力模式及回正模式下的控制策略,并在MATLAB/Simulink环境下进行了仿真。仿真结果表明,商用车辆加装EPS后反应更迅速,操纵稳定性、转向轻便性得到了提高。同时,在加入回正控制后,转向回正特性也得到了改善。     

食窦魏斯氏菌SJ-02产胞外多糖发酵工艺优化

采用响应面法对影响食窦魏斯氏菌SJ-02(Weissella cibaria SJ-02)产胞外多糖(exopolysaccharides,EPS)的发酵培养基组分和发酵条件进行优化。以EPS产量为指标,首先探究培养基中碳源、氮源对EPS产量的影响,结果表明,以MRS为基础培养基,维持2%葡萄糖不变、用1.5%大豆蛋白胨替代蛋白胨,可增加菌株SJ-02的EPS产量;在单因素试验基础上采用Box-Behnken中心组合试验设计对影响EPS产量的因素进行优化,获得菌株SJ-02产EPS的最适发酵条件:接种量3.00%、培养时间34h、培养温度37℃,在此条件下理论预测EPS产量为335.03 mg/L,验证实验测得EPS产量为331.47mg/L,比未优化前提高了17%。     

根瘤菌胞外多糖的分离纯化及组分分析

以根瘤菌发酵液为原料,提取纯化发酵液中胞外多糖(extracellular polysaccharides,EPS),并对其多糖组分进行分析。采用木瓜蛋白酶与sevage法结合脱蛋白,并利用柱层析法对胞外多糖进行单组分离和纯化,分别得到EPS 1-1、EPS 2-1、EPS 3-1、EPS 4-1和EPS 5-1等5种相对较纯的单一组分。分别采用不同色谱法对上述各单一组分的纯度、结构、相对分子量及单糖组成进行分析和测定,表明各个组分均具有多糖特征峰,且均是以β-型糖苷键连接的吡喃糖,其中EPS 1-1和EPS 3-1是β构型的半乳吡喃糖; 5种多糖组分均主要由具有不同摩尔比的半乳糖、葡萄糖和甘露糖组成,除了EPS 4-1之外,在其他组分中还检测到了不同含量的岩藻糖、鼠李糖和阿拉伯糖等。     

1株高产EPS嗜热链球菌的筛选及培养条件优化

为了研究乳酸菌高产EPS的条件,以产EPS量为指标,从8种复合菌株中筛选出1株嗜热链球菌,通过单因素和正交试验对该菌EPS合成培养基中的碳源、氮源、培养条件进行了研究。结果显示:该菌在优化的培养基中EPS生成量可达到145.48mg/L;合成胞外多糖最适培养条件为:接种量2%,初始pH6.5,发酵温度34℃,发酵时间36h。在此条件下EPS生产量可高达270mg/L,提高了116%。因此氮源组合和pH值为影响EPS合成的显著因素(p<0.05)。在恒定pH值条件下发酵培养可以提高EPS的生成量,即474mg/L,又提高了72%。     

根瘤菌胞外多糖的结构与功能研究进展

介绍了豆科植物根瘤菌产生的胞外多糖(EPS)的结构、合成与调控,综述了EPS的信号、免疫调节和抗肿瘤的功能。     

ADSA Foundation Scholar Award: Possibilities and challenges of exopolysaccharide-producing lactic cultures in dairy foods

Exopolysaccharides (EPS) from lactic acid bacteria are a diverse group of polysaccharides exhibiting various functional properties. Two forms of EPS are produced by lactic acid bacteria: capsular and unattached. Capsular EPS does not cause ropiness nor does production of unattached EPS ensure ropiness. The functions of EPS in dairy products are not completely understood. This is for 2 main reasons: the major variations among exopolysaccharides even from the same group of micro-organisms, which makes it difficult to apply information from one EPS to others, and the lack of availability of techniques with the ability to observe the microstructure and distribution of the highly hydrated EPS in fermented dairy products. The introduction of relatively new microscopic techniques such as confocal scanning laser microscopy and cryo-scanning electron microscopy made it possible to directly observe the distribution of fully hydrated EPS in dairy products. Recently, EPS produced by nonropy strains have drawn the attention of the dairy industry. This is because of the ability of some nonropy strains to produce large capsular and unattached EPS that would improve the texture of dairy products without causing the undesirable slippery mouthfeel produced by the ropy strains. Factors affecting functions of EPS are their molecular characteristics and ability to interact with milk proteins. Studying the interaction between EPS and milk proteins is complex because EPS are gradually produced during fermentation, unlike polysaccharides added directly to milk to stabilize the fermented product. The concentration and possibly molecular characteristics of EPS and protein characteristics such as charge and hydrophobicity change during fermentation. Consequently, the interaction of EPS with proteins might also change during fermentation. Exopolysaccharides provide functions that benefit reduced-fat cheeses. They bind water and increase the moisture in the nonfat portion, interfere with protein-protein interactions and reduce the rigidity of the protein network, and increase viscosity of the serum phase. This review discusses the production of capsular EPS and their role in structure formation in fermented milk, the mechanism of ropiness formation, and applications of EPS-producing cultures in reduced-fat cheeses.     

Effect of medium composition and temperature and pH changes on exopolysaccharide yields and stability during Streptococcus thermophilus LY03 fermentations

To increase the exopolysaccharide (EPS) yields from Streptococcus thermophilus LY03 and to unravel the nature of the EPS degradation process, fermentation experiments were carried out with this strain in a customized MRS medium, using different additional carbohydrates or amino acids possibly related to growth and EPS production. No significant increase of the EPS yields or activities of the enzymes alpha-phosphoglucomutase, UDP-glucose pyrophosphorylase and UDP-galactose 4-epimerase that are correlated with EPS production, or of the activity of dTDP-glucose pyrophosphorylase involved in the rhamnose synthetic branch of EPS biosynthesis, was observed. The EPS monomer composition remained unchanged for all experiments. Fermentations with a sudden temperature increase or lowered pH were carried out as well to try to avoid EPS degradation upon prolonged fermentation. It was demonstrated that EPS degradation took place enzymatically. Incubations of purified high-molecular-mass EPS with cell-free culture supernatant or cell extracts showed its degradation by enzymes with an endo-activity. This glycohydrolytic activity probably encompasses several enzymes having a molecular mass lower than 50,000 and 10,000 Da, and seems to be rather stable at high temperature and low pH. These results contribute to a better understanding of the physiological and chemical factors influencing EPS production and degradation.     

Growth and exopolysaccharide yield of Lactobacillus delbrueckii ssp. bulgaricus DSM 20081 in batch and continuous bioreactor experiments at constant pH

Some Lactobacillus delbrueckii ssp. bulgaricus strains are able to synthesize exopolysaccharides (EPS) and are therefore highly important for the dairy industry as starter cultures. The aim of this study was to investigate the nutritional requirements for growth and EPS production of Lactobacillus delbrueckii ssp. bulgaricus DSM 20081. A medium was developed from a semi-defined medium (SDM) in which glucose was replaced by lactose and different combinations of supplements (nucleobases, vitamins, salts, sodium formate and orotic acid) were added. Constant pH batch fermentation with the modified medium resulted in an EPS yield of approximately 210 mg glucose equivalents per liter medium. This was a 10-fold increase over flask cultivation of this strain in SDM. Although not affecting cell growth, the mixture of salts enhanced the EPS synthesis. Whereas EPS production was approximately 12 mg/g dry biomass without salt supplementation, a significantly higher yield (approximately 20 mg/g dry biomass) was observed after adding the salt mixture. In continuous fermentation, a maximal EPS concentration was obtained at a dilution rate of 0.31/h (80 mg EPS/L), which corresponded to a specific EPS production of 49 mg/g dry biomass.     

Anaerobic electrochemical corrosion of mild steel in the presence of extracellular polymeric substances produced by a culture enriched in sulfate-reducing bacteria

The corrosion of mild steel in a seawater medium containing extracellular polymeric substances (EPS) produced by sulfate-reducing bacteria (SRB) was studied by electrochemical experiments and atomic force microscopy (AFM). Under anaerobic conditions, the corrosion of mild steel increased up to 5-fold in the presence of a 1% (w/w) EPS solution but in the absence of SRB. The enhanced corrosion is mainly due to the oxidizing power of EPS with a reduction potential of E1/2 at -0.54 V (saturated calomel electrode), which is 0.4 V above that of hydrogen reduction. The electrochemical reduction of EPS provides a couple to iron oxidation, as demonstrated by H-shaped cell experiments in which the steel sample and EPS are not in physical contact but are ionically connected via the solution and electronically connected through an external wire. Fourier transformation infrared spectroscopy and X-ray photoelectron spectroscopy showed that EPS derived from SRB are comprised of 60% proteins, 37% polysaccharides, and 3% hydrocarbons. The XPS results showed that, upon corrosion, polysaccharide components were mostly converted to hydrocarbons.     

巴西虫草胞外多糖提取工艺的优化

研究了巴西虫草液体发酵胞外多糖的提取条件,通过单因素试验选取各因素的水平,根据Box-Benhnken的中心组合试验设计原理,进行响应面回归分析,以胞外多糖量为响应值,确定了胞外多糖提取工艺中各影响因素的水平,结合验证实验结果得到了最佳的工艺条件。     

芽孢杆菌胞外多糖的结构初步分析

从筛选自新疆罗布泊沙漠的1株芽孢杆菌的发酵滤液中分离得到胞外多糖EPSⅠ和EPSⅡ,其中EPSⅠ为主要成分,占总糖的89.5%,EPSⅠ为糖蛋白,其分子质量为96.292ku,多糖含量为93.79%,蛋白含量为5.62%,不含糖醛酸,是由D-N-乙酰葡萄糖胺,D-木糖和D-甘露糖构成,它们的摩尔比例是2.36∶0.98∶1.75。EPSⅠ为β型吡喃糖,经高碘酸氧化和Smith降解,EPSⅠ中含有(1→),(1→3)和(1→4)糖苷键,且(1→)和(1→4)糖苷键的比例为1∶24.05,其中的糖肽是O-糖苷键。     

Uncoupling of growth and exopolysaccharide production by Lactococcus lactis subsp. cremoris NIZO B40 and optimization of its synthesis

Exopolysaccharide (EPS) production by Lactococcus lactis subsp. cremoris NIZO B40 was found to be most efficient with glucose as a substrate. The optimal temperature and pH for EPS synthesis were 25 degrees C and pH 5.8, respectively. EPS production could not be identified as a stress response: increased oxygen tension and reduced water activity negatively affected both growth and EPS synthesis. It is often assumed that there is a competition between growth and EPS formation. Within the range of 0.5 and 0.1 h(-1), reducing the growth rate resulted indeed in an increase of the specific EPS production but the polymer formation decreased again at even lower growth rates. Most of the applied fermentation conditions influenced both growth and EPS formation. As the growth rate itself also influenced EPS formation, we studied the linking between growth and EPS synthesis. Interestingly, EPS production was not strictly coupled to growth. Significant de novo synthesis of EPS was observed in non-growing cultures. Consequently, the influence of different culture conditions on EPS production could be studied independent of growth.     

芽孢杆菌活性多糖的分离纯化及合成基因研究

选用自行选育的1 株活性多糖高产菌株（Bacillus amyloliquefaciens LPL061）,经醇沉、除蛋白、透析、冷冻干燥从其发酵上清中分离得到活性多糖粗品,并采用色谱纯化技术进一步纯化,得到1 个中性糖组分（EPS1）和1 个酸性糖组分（EPS2）。根据GeneBank中已报道芽孢杆菌产糖相关基因设计引物,经PCR扩增获得解淀粉芽孢杆菌LPL061的5 个EPS生物合成相关基因。对其功能预测分析表明这些基因主要参与EPS合成过程多糖聚合、糖基转移、糖链长度控制以及多糖转运和输出。