g-氨基丁酸的色谱分离

从8种树脂中筛选出能将g-氨基丁酸与谷氨酸钠分离的最佳树脂,考察了色谱柱高径比、洗脱流速、柱温对分离度和回收率的影响,用g-氨基丁酸发酵液上样,研究了发酵液的分离效果. 结果表明,树脂QY-HG01能将g-氨基丁酸与谷氨酸钠高效分离;在高径比25、流速2.5 mL/min、柱温50℃的条件下,g-氨基丁酸与谷氨酸钠的分离效果最好;用预处理的g-氨基丁酸发酵液上样,发酵液脱色率为84.9%,脱盐率为99.2%,g-氨基丁酸的纯度由24.9%提高到84.0%,回收率为89.3%.     

复合乳酸菌发酵生产天然鲜奶香基的研究

通过吖啶橙诱变提高乳酸菌的脂肪酶和蛋白酶活性,结合感官评定发酵乳风味,筛选得到了具有产香潜力的7株乳酸菌突变菌。组合各株产香菌共发酵,得到了一个能产生鲜奶香基的菌株组合。该组合在以蔗糖-葡萄糖（2∶1）为碳源、添加0.5%柠檬酸铵的牛乳产香培养基中,42℃条件下连续发酵菌株La2、Lc1和St2 12 h,发酵液均质后能作为鲜奶香基直接应用。     

乳酸菌微生物燃料电池产电性能及产电机理研究

采用双室微生物燃料电池（MFC）,以乳酸菌为产电微生物,并以葡萄糖为唯一的电子供体,研究MFC的产电性能以及乳酸菌MFC产电机理。在30 ℃下,底物浓度为1.5 g/L时,该MFC的开路电压稳定在500 mV。实验条件下测得该MFC的最大功率密度为393.23 mW/m²,内阻约为500 Ω。利用气相色谱分析乳酸菌MFC产电过程中代谢产物的含量变化,实验数据表明无论是不参与产电的正常代谢途径还是产电过程中,都涉及到乳酸菌的同型乳酸发酵途径、异型乳酸发酵的经典途径和双歧杆菌发酵途径。在乳酸菌MFC运行过程中人为添加乙醇,该实验结果显示乙醇不利于乳酸菌产电,表明乳酸菌的异型乳酸发酵途径是乳酸菌进行产电的关键代谢途径。     

Gamma-Aminobutyric Acid Production Using Immobilized Glutamate Decarboxylase Followed by Downstream Processing with Cation Exchange Chromatography

We have developed a gamma-aminobutyric acid (GABA) production technique using his-tag mediated immobilization of Escherichia coli-derived glutamate decarboxylase (GAD), an enzyme that catalyzes the conversion of glutamate to GABA. The GAD was obtained at 1.43 g/L from GAD-overexpressed E. coli fermentation and consisted of 59.7% monomer, 29.2% dimer and 2.3% tetramer with a 97.6% soluble form of the total GAD. The harvested GAD was immobilized to metal affinity gel with an immobilization yield of 92%. Based on an investigation of specific enzyme activity and reaction characteristics, glutamic acid (GA) was chosen over monosodium glutamate (MSG) as a substrate for immobilized GAD, resulting in conversion of 2.17 M GABA in a 1 L reactor within 100 min. The immobilized enzymes retained 58.1% of their initial activities after ten consecutive uses. By using cation exchange chromatography followed by enzymatic conversion, GABA was separated from the residual substrate and leached GAD. As a consequence, the glutamic acid was mostly removed with no detectable GAD, while 91.2% of GABA was yielded in the purification step.     

有机溶剂透性化处理谷氨酸脱羧酶工程菌制备γ-氨基丁酸的研究

为了降低细胞壁和细胞膜的传质阻力对全细胞催化过程的不利影响,采用有机溶剂对表达重组谷氨酸脱羧酶(GAD)的工程菌BL21(DE3)-p ET28a-gad B进行了透性化处理。结果表明,菌体GAD表观催化活力的改善程度与有机溶剂的介电系数和疏水性具有较强相关性,低介电常数(6),高疏水性(log P0.68)的有机溶剂可以有效提高工程菌的GAD催化活性,其中最有效的透性化试剂为二甲苯(介电常数为2.4,log P为3.1)。当二甲苯的用量为5μL?mg?1(干重细胞)、处理时间5 min时,菌体表观催化活力达到最优值,为7.94 U?mg?1(干重细胞),是处理前表观催化活力的12.4倍。为了充分利用菌体的催化活力,采用海藻酸钙包埋的方法对二甲苯处理过的菌体进行固定化,结果发现固定化的透性化菌体可以较好地保持催化活力,反复催化10次后发现,第10次的GABA产率为第1次GABA产率的72.04%。研究为系统的选择有机溶剂来有效提高GAD工程菌表观催化活性提供了参考,同时制备的固定化的透性化菌体显示了良好工业应用前景。     

由乳酸菌制备维生素B类化合物的研究进展

维生素B类化合物是人体必需物质,主要通过外源性的食物或药物来补充。选育得到的乳酸菌能产生天然的人体易于吸收的不同类型维生素B。介绍了近年来通过乳酸菌生物合成维生素B类化合物的研究进展,为进一步研究产维生素B类化合物乳酸菌菌种选育和代谢工程改造提供参考。     

利用糖蜜废水产乳酸细菌的分离与鉴定

为获得可利用糖蜜废水产生乳酸的细菌,采用厌氧Hungate培养技术,从糖蜜废水处理生物反应器中获得活性污泥,分离到一株乳酸菌MD-9。对该株细菌进行了形态学特征、生理生化指标、16S rRNA基因序列分析等研究。结果表明与最相近的种属Lactobillus fermnetus的16S rRNA基因序列同源性为99.6%。该株细菌为兼性厌氧杆菌,葡萄糖代谢特征为专性异型发酵,可以利用糖蜜废水产生乳酸。     

Differentiation of pH and free lactic acid effects on the various growth and production phases of lactobacillus helveticus

Growth and acid production coupling for Lactobacillus helveticus was found to be mainly controlled by cultivation pH. The kinetics of the two processes were uncoupled at acidic pH. This conclusion has been established by means of a simple plot, under conditions where the nitrogen source was not limiting. During the deceleration phase, the acid production rate remained close to its maximal value at a given cultivation pH, while growth rate decreased notably. Both growth and acid production were inhibited by undissociated lactic acid accumulated in the medium, but the growth rate was shown to be more affected than acid production. For the strain of L helveticus used throughout this work, irrespective of cultivation pH, concentrations of free lactic acid of 8.5 and 13.4 g dm⁻³ resulted in a full inhibition of growth (leading to a stationary phase) and acid production respectively. These findings will be useful to optimize the mean volumetric acid productivity of batch fermentations, both at constant and programmed pH values. © 1999 Society of Chemical Industry     

Unstructured model for seed cultures without pH control of Lactobacillus helveticus growing on supplemented whey permeate

In cultures of Lactobacillus helveticus with pH controlled at 5.9, growth and lactic acid production were under the control of nutritional limitations (carbon and nitrogen). In the absence of pH control, as was the case for seed cultures, an inhibitory effect on growth of both pH and the undissociated lactic acid concentration were evident before nutritional limitations. The variations of the specific growth rate with the undissociated lactic acid concentration followed exponential decay. Then, the inhibitory effect of pH was also taken into account through the Henderson–Hasselbach equation. The specific growth rate history has been previously found to follow sigmoidal variation. Integration of these relationships gave the theoretical biomass and lactic acid production kinetics. The model fitted experimental kinetic data well and allowed fine analysis of the various growth phases, since the growth‐associated, the deceleration and the stationary states can be characterized by means of the model parameters. © 2002 Society of Chemical Industry     

Feed supplement recovered from dairy wastewater by biological and chemical pretreatment

A continuous process for treatment of dairy wastewater with immobilized lactic acid bacteria has been demonstrated at pilot scale. A strain of Lactobacillus plantarum was selected on the basis of a high conversion rate of lactose at low pH, a high affinity of lactose at low concentrations, and the ability to retain activity for a long time immobilized in alginate beads. Lactose was converted to lactic acid, which lowered the pH and precipitated milk proteins. The proteins were separated together with milk fat by flotation with carboxy methyl cellulose (CMC) or chitosan and gave a solid phase of approx. 10% dry matter (23% protein and 68% fat). The total chemical oxygen demand (COD_t) removed varied from 65 to 78% for CMC and 49 to 82% for chitosan. The precipitated material was used as a feed supplement for pigs to provide up to 30% of the total energy intake. No adverse effects on the pig's performance were observed. The energy feed value of the precipitate was estimated to be 2·0 feed units (FUs) per kg dry matter. © 1998 Society of Chemical Industry     

Molecular Detection of Two Potential Probiotic Lactobacilli Strains and Evaluation of Their Performance as Starter Adjuncts in Yogurt Production

A molecular method for efficient and accurate detection and identification of two potential probiotic lactobacilli strains isolated from fermented olives, namely Lactobacillus pentosus B281 and Lb. plantarum B282, was developed in the present study. Random Amplified Polymorphic DNA (RAPD) analysis was performed, and strain specific primers were designed and applied in a multiplex polymerase chain reaction (PCR) assay. The specificity of the assay was tested and successfully confirmed in 27 and 22 lactobacilli strains for Lb. pentosus B281 and Lb. plantarum B282, respectively. Moreover, the two strains were used as starter cultures in yogurt production. Cell enumeration followed by multiplex PCR analysis demonstrated that the two strains were present in yogurt samples at levels ≥6 log CFU/g even after 35 days of storage at 4 °C. Microbiological analysis showed that lactobacilli and streptococci were present within usual levels, whereas enterobacteriaceae and yeast/mold counts were not detected as expected. Although the pH values of the novel products were slightly lower than the control ones, the yogurt containing the probiotic cultures scored similar values compared to the control in a series of sensory tests. Overall, these results demonstrated the possible use of the two strains as starter adjuncts in the production of yogurt with potential probiotic properties.     

乳酸脱氢酶的分离纯化及其催化合成苯乳酸的研究进展

对乳酸脱氢酶的来源、分离纯化及其催化合成苯乳酸的研究进行了综述。首先;分析了乳酸脱氢酶的微生物来源;重点对乳酸菌中乳酸脱氢酶的分离方法及相关研究现状进行了总结;认为采用晶胶层析方法可直接一步从破胞液中分离高纯度的乳酸脱氢酶;然后;分析了乳酸脱氢酶催化苯丙酮酸的核心反应机理、最适条件及其工程改造;讨论了pH、温度、耐热性等参数对乳酸脱氢酶催化苯丙酮酸的影响;表明不同菌种乳酸脱氢酶催化苯丙酮酸最适pH和温度有很大差异;最后;对比了乳酸脱氢酶酶法合成苯乳酸相关工程改造的研究工作;指出基因修饰能有效提高乳酸脱氢酶酶法对苯丙酮酸的催化能力;同时乳酸脱氢酶与辅酶共表达体系的构建是下一步研究的重点方向。     

乳酸菌处理虾壳发酵液总酸度的测定方法研究

采用常规滴定法和电位滴定法测定乳酸菌处理虾壳发酵液的总酸度,并通过F检验法和t检验法判断两种方法精密度和准确度之间是否存在显著性差异。结果表明,发酵液稀释20倍可以降低溶液颜色对实验结果的影响,提高测试结果的准确度。微型常规滴定法可以取得与常量滴定法一样的结果,但对实验人员的实验技能要求较高。电位滴定法和微型常规滴定法的精密度和准确度均不存在显著性差异,均适合于测定产乳酸、蛋白酶菌发酵脱除虾壳钙盐和蛋白质制得甲壳素发酵液的总酸度。     

用乳酸细菌从有机废弃物生产乳酸

探讨了有机废物乳酸发酵的影响因素,包括菌种、营养物质、产物抑制、氧气和发酵方式,概述了利用含碳水化合物的有机废弃物和厨房垃圾生产乳酸的现状,并对未来的研究方向提出了展望。指出在厌氧条件下应用同型发酵乳酸细菌,采用原位产物分离技术和细胞再循环发酵通常会提高乳酸的产量;采取多菌种的联合发酵并优化提取工艺,将有助于实现有机废物工业化生产乳酸。