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。     

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。     

荷叶离褶伞中试发酵条件与培养基优化研究

在荷叶离褶伞菌丝体摇瓶发酵条件研究结果的基础上,采用均匀设计,在200L发酵罐中,对荷叶离褶伞中试发酵条件与培养基配方进行了优化研究,结果表明荷叶离褶伞菌丝体中试发酵的最佳条件为搅拌转速160r/min、罐压0.2MPa、通气量80L/h、pH值为6.5、温度20℃、接种量10%;最佳培养基配方为玉米面5%、大豆0.5%、ZnSO4 0.025%、MgSO4 0.05%、KH2PO4 0.05%。发酵至第8d菌丝体生物量达到最大(10.578g/L),第9d胞外多糖(exopolysaccharides,EPS)产量最大(1.212g/L)。     

嗜热链球菌产胞外多糖的培养条件及分离提取

以高产胞外多糖的西藏雪莲嗜热链球菌为菌株,IRIE培养基为基础培养基,研究了影响嗜热链球菌产胞外多糖培养条件及多糖提取的工艺条件。采用正交实验法分析了温度、时间及接种量对嗜热链球菌胞外多糖产量的影响。结果表明嗜热链球菌培养的最佳条件为:3%接种量,42℃发酵48h,粗多糖含量为382.8mg/L。多糖提取工艺的研究结果表明:Sevage法脱蛋白3次、上清液超滤(滤膜MWCO3ku,压力0.2×105Pa,温度25℃)浓缩4倍,多糖的提取效果最好。     

产胞外多糖乳酸菌的筛选及抗氧化特性研究

以分离自贵州侗族、苗族传统发酵食品的36株乳酸菌为受试菌,筛选出8株高产胞外多糖（膜截留分子质量为8 000~14 000 u）的乳酸菌,分别为SR2-1（Pediococcus sp. F3S1）、SR2-2（Pediococcus pentosaceus NGRI 0304）、SR3-2（Pediococcus pentosaceus LB-WC）、SR8（Lactobacillus kimchi）、SR10-2（Pediococcus sp. 22-4）、SR12-1（Lactobacillus graminis）、H1（Staphylococcus sp. 3034O2）和XS2（Pediococcus pentosaceus GS17）,并对其胞外多糖进行体外抗氧化特性研究。结果显示,8株乳酸菌的胞外多糖均具有抗氧化活性,其中胞外多糖质量浓度为30 μg/mL时,乳酸菌SR2-2、SR8和SR12-1的胞外多糖对Fe2+的清除率分别为15.55%、12.41%、53.21%;胞外多糖质量浓度为40 μg/mL时,乳酸菌SR2-2、SR8和SR12-1的胞外多糖对1,1-二苯基-2-三硝基苯肼（DPPH·）和NO2-的清除率分别达9.69%、11.93%、8.93%及5.73%、7.82%、3.82%。这三株乳酸菌显示出一定的抗氧化活性。     

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%。     

Evaluation of the yield,molar mass of exopolysaccharides,and rheological properties of gels formed during fermentation of milk by Streptococcus thermophilus strains St-143 and ST-10255y

The yield and chemical structures of exopolysaccharides (EPS) produced by many strains of Streptococcus thermophilus have been characterized. However, the kinetics (or production profile) for EPS during milk fermentation is not clear. In this study, we investigated whether any differences existed in the yield and molar mass of EPS when milk was fermented at the same acidification rate by 2 strains of S. thermophilus (St-143 and ST-10255y). The type of EPS produced by these 2 strains is different. Milk samples were analyzed for EPS concentration every 30 min during a fermentation period of 270 min (final pH 4.5) by using a modified quantification method, which was faster and validated for its recovery of added EPS. Rheological properties of milks during fermentation were also analyzed using small-strain dynamic oscillatory rheology. For the determination of molar mass, EPS extracts were isolated by ultrafiltration of whey obtained during fermentation of milk to pH values 5.2, 4.9, 4.7, and 4.5, and molar mass was analyzed using size-exclusion chromatography–multi-angle laser light scattering. During fermentation, both strains appeared to start producing significant amounts of EPS after about ～150 min, which corresponded to pH ～5.3, which was close to the point of gelation. During the remainder of the fermentation process (150–270 min), the EPS concentration from strains St-143 and ST-10255y significantly increased from 30 to 72 mg/L and from 26 to 56 mg/L, respectively. The quantity of EPS recovered by our modified method was estimated to represent ～60% of the total EPS added to milk. The molar mass of EPS produced by both strains appeared to slightly decrease during fermentation. At pH 5.2, EPS from St-143 and ST-10255y had molar masses of 2.9 × 10⁶ and 1.4 × 10⁶ g/mol, respectively, which decreased to 1.6 × 10⁶ and 0.8 × 10⁶ g/mol, respectively, when the pH of milk was 4.5. Distinct differences were apparent in the rheological properties of gels fermented by the 2 strains. At the end of fermentation, St-143 fermented milk had weaker gels with storage modulus (G′) value at pH 4.6 of 26 Pa, whereas gels made with ST-10255y were stiffer with a G′ value at pH 4.6 of 82 Pa. For St-143 gels, maximum loss tangent (LT_max) values were higher (0.50) and occurred earlier (at a higher pH value) than the LT_max values (0.46) for gels from ST-10255y strain. Because the fermentation conditions were identical for both strains, the observed changes in rheological properties could be due to the differences in chemical structures and molar mass of the EPS produced by these 2 S. thermophilus strains.     

植物乳杆菌YM-2菌株胞外多糖生物合成工艺优化

对从云南传统发酵豆豉分离得到的植物乳杆菌YM-2(Lactobacillus plantarum YM-2)菌株胞外多糖(exopolysaccharide,EPS)生物合成条件进行优化。首先对培养基成分中的碳源、氮源种类进行筛选;然后利用单因素试验分析碳源含量、氮源含量、培养时间以及培养温度对EPS产量的影响;最后采用Box-Behnken法进行四因素三水平响应面分析以确定其最优工艺条件。结果表明,植物乳杆菌YM-2菌株生物合成EPS最佳条件为碳源(葡萄糖)含量30 g/L、氮源(酵母粉)含量30 g/L、培养时间30.05 h、培养温度36.36℃,在此工艺条件下,植物乳杆菌YM-2 EPS产量为257.362 mg/L。     

双歧杆菌对肿瘤治疗作用的研究进展

双歧杆菌是人体肠道中重要的有益菌群,具有改善胃肠道功能和预防疾病等诸多功能。最新研究表明其在肿瘤治疗中亦有应用前景。传统肿瘤治疗方法会在治疗过程中产生较强的毒副作用。随着科学研究的不断深入,一些新的肿瘤治疗方法业已投入临床应用。肿瘤免疫治疗可通过激发机体自身免疫系统对肿瘤细胞进行杀伤和清除。研究发现双歧杆菌在肿瘤免疫治疗中可发挥双重作用,既可激活抗肿瘤免疫应答,又可缓解免疫检查点疗法引起的副作用。同时,双歧杆菌在肿瘤靶向性基因治疗中可作为载体将药物运输到实体瘤内部并发挥治疗作用。文章在介绍双歧杆菌对机体主要作用的基础上对其在肿瘤治疗中的最新应用进行了综述。