乳酸乳球菌KLDS4.0325产细菌素最佳培养条件的研究

以分离自新疆牧民家庭自制酸马奶中的乳酸乳球菌KLDS4.0325为研究对象,以大肠杆菌为指示菌,以抑菌圈直径为考察指标,考察了不同温度、p H、转速及培养时间等培养条件对该菌株细菌素产量的影响,经单因素实验优化得出乳酸乳球菌KLDS4.0325在培养温度33℃,培养基初始p H7.0,120 r/min摇床培养20 h的条件下,无细胞发酵上清液对大肠杆菌的抑菌圈直径最大,抑菌活性最强,细菌素产量最高。在此条件下,抑菌圈直径为25.26 mm,细菌素效价可达5383.07 IU/m L。      

乳酸乳球菌乳酸亚种产丁二酮的优化研究

分别研究了10种不同因素对乳酸乳球菌乳酸亚种产生丁二酮含量的影响。实验结果表明,各因素产生丁二酮最高量的条件分别为:培养温度为37℃,凝乳后0h,后熟12h,培养基pH调节为5.6,培养基中添加柠檬酸的量为0.15%;培养基中添加Vc的量为0.01%,培养基中添加金属离子的量分别为Mg2+0.03%、Cu2+0.02%、Mn2+0%,培养基中添加甘氨酸的量为0.2%,培养基中添加碳水化合物的量分别为葡萄糖为0%、蔗糖为0%;随着基质浓度增加丁二酮产量也随之增加。     

乳酸乳球菌乳酸亚种高产胆盐水解酶发酵条件的优化研究

本文利用从藏灵菇中筛选的产胆盐水解酶的乳酸乳球菌乳酸亚种(Lactococcuslactissubsp.lactis)研究提高酶活力的环境因素。针对主要影响胆盐水解酶合成的四个因素,采用四因素三水平L9(34)正交试验确定了高产胆盐水解酶优化发酵条件:葡萄糖添加量为3%、大豆蛋白胨添加量为2%、发酵温度为37℃、接种量为2%。在优化条件下,胆盐水解酶活力是优化前的11.84倍。     

补料策略优化促进乳酸乳球菌HB03发酵合成Nisin

为提高乳酸乳球菌HB03发酵合成Nisin的效率,本研究基于乳酸乳球菌发酵生长期间存在的氧化胁迫效应和胞外氨基酸消长规律,分析了肽水解酶系、UMP从头合成和肽聚糖合成代谢在转录组水平的表达差异,确定对数中后期Nisin合成限制因素为半胱氨酸（cysteine,Cys）和精氨酸（arginine,Arg）供应不足,并通过氨基酸单因素和碳氮源补加优化,确定10 L发酵罐水平优化的补料策略为：11、13.5、17、19.5 h分别加入0.15 mmol/L的Cys,12 h补入蛋白胨（15 g/L）,10～24 h补入蔗糖（1.5 g/（L·h））,12～21 h流加Arg(0.25 g/（L·h）)。在此条件下Nisin效价达到了8 963 IU/m L,比只补加Cys发酵效价（6 993 IU/m L）提高了28.2%,研究结果可为Nisin工业发酵提供重要参考。     

乳酸乳球菌K6产Nisin Z的条件优化

本文以贻贝中筛选分离出来的乳酸乳球菌K6为研究对象,以细菌素抑制金黄色葡萄球菌的半抑制浓度(MIC50)为考察指标,优化乳酸乳球菌K6产乳酸链球菌素Z(Nisin Z)的条件。首先研究培养基、培养基初始pH值、菌液添加量、培养时间和温度5个因素对Nisin Z抑菌效果的影响,确定培养温度、培养时间和培养基初始pH值3个因素为显著因素,然后利用响应面法优化这3个因素。最终获得产Nisin Z的优化条件为:培养基初始pH 7.5,培养温度29.8℃,培养时间9 h。经过条件优化后,该细菌产细菌素抑菌浓度为0.625 BU/mL,较优化前细菌素浓度提高了8倍。优化后的细菌素对金黄色葡萄球菌具有抑制作用。在最优条件下的试验结果与模型预测值接近,说明所建模型切实可行。     

乳酸乳球菌乳脂亚种高产丁二酮的条件优化

分别研究了10种不同因素对乳酸乳球菌乳脂亚种产生丁二酮质量分数的影响.结果表明,各因素产生丁二酮最高量的条件:培养温度为37℃;凝乳后3 h;后熟12 h;培养基pH值调至为5.6;培养基中添加柠檬酸氢二铵的质量浓度为0.15%:培养基中添加Vc的质量浓度为0.3%.培养基中添加金属离子的质量浓度分别为:Mg2+为O.05%,Cu2+为O.04%,Mn2+为O.001%;培养基中添加甘氨酸的质量浓度为1.7%(均为质量分数);培养基中添加碳水化舍物的质量浓度分别为:葡萄糖为1%,蔗糖为1.5%(均为质量分数);随着基质浓度增加丁二酮产量也随之增加.     

乳酸乳球菌L9产类细菌素lactococcin GJ-9发酵条件的研究

对产类细菌素乳酸乳球菌L9的发酵条件进行了研究。结果表明 :产类细菌素最适培养基为MRS,培养基的最适初始pH值为 6 5 ;产类细菌素最适温度为 32℃ ;0 2 %Tween 80最适类细菌素的产生。并通过正交试验确定L9产类细菌素的最佳培养基为 :大豆蛋白胨 1 %、酵母膏1 5%、葡萄糖 1 2 5 %、K2 HPO40 2 %、NaAc 0 5 %、MgSO4·7H2 O 0 0 58%、柠檬酸三铵 0 2 %、MnSO4·4H2 O 0 0 0 5 %、Tween 80 0 2 % ;初始 pH6 0。经过优化 ,发酵液效价提高了 61 0 7%。     

固定化乳酸乳球菌DL-203发酵生产Nisin的研究

对用固定化乳酸乳球菌DL-203发酵生产Nisin进行了研究。确定采用k-卡拉胶作为固定化载体,并添加磷酸三钙,包埋固定化乳酸乳球菌DL-203发酵生产Nisin。固定化最适条件为3.5%（W/V）k-卡拉胶+0.1%（W/V）磷酸三钙,细胞浓度5%～10%（V/V）。发酵培养基添加0.2%（V/V）吐温-20,30℃摇床培养进行分批重复发酵,可连续使用五批以上,而发酵液Nisin效价未有下降,达游离细胞发酵液的50%～60%。采用柱式填充床反应器进行固定化乳酸乳球菌DL-203连续发酵生产Nisin,停留时间以4～6h比较适宜,可连续稳定生产150h以上,而且固定化小球未有明显的细胞外漏,发酵液Nisin效价可达游离细胞发酵液的30%～40%。      

乳酸乳球菌乳酸亚种的m6A甲基化差异研究

乳酸乳球菌乳酸亚种是常用的工业发酵剂菌种,具有较高的经济价值.乳酸乳球菌乳酸亚种BL19与IMAU10978的发酵特性存在较大差异,其中BL19具有良好发酵特性.本文比较2株存在明显发酵特性差异的乳酸乳球菌乳酸亚种BL19与IMAU10978,从基因组与m6A甲基化角度探究2株菌的发酵差异化特性.通过单分子实时(SMR...     

产片球菌素的乳酸片球菌培养条件的优化

通过正交实验对从泡菜中分离出的一株乳酸片球菌进行发酵条件的研究,结果发现乳酸片球菌素的产量除了与菌株自身性质有关外,其他发酵条件对片球菌素的产量和活性也有影响,包括培养基组分、培养基pH、培养温度以及培养时间,实验确定了产片球菌素的最佳培养基成分、最佳培养pH、最佳培养温度和最佳培养时间。      

微波诱变对乳酸乳球菌Nisin产量的影响

用微波诱变Nisin产生茼，获得一突变菌株WY-4，用琼脂扩散法测得WY-4菌株的生物效价为511．56IU/mL．比原始菌株提高42．13％。遗传稳定实验证明其遗传性状稳定。     

INHIBITION OF LISTERIA MONOCYTOGENES BY LACTOCOCCUS LACTIS SUBSP. LACTIS ISOLATED FROM ITALIAN RAW HAM

A total of 168 strains of lactic acid bacteria were isolated from Italian raw ham and screened for antagonistic activity against Listeria monocytogenes by using an agar spot assay. Only one strain of Lactococcus lactis subsp . lactis produced antagonistic effects other than inhibition by low pH and hydrogen peroxide. The proteinaceous nature of the compound produced by L. lactis B10 was demonstrated by its inactivation by proteolytic enzymes. The cell-free culture super-natants (filtered and heat-treated) showed a bactericidal mode of action. Bacteriocin produced by L. lactis B10 was inhibitory to other lactic acid bacteria and one strain of Staphylococcus aureus, but not to the gram-negative bacteria tested .     

PURIFICATION AND CHARACTERIZATION OF OLIGOMERIC SPECIES OF AN AROMATIC AMINO ACID AMINOTRANSFERASE FROM LACTOCOCCUS LACTIS SUBSP. LACTIS S3

Two oligomeric species of an aromatic amino acid aminotransferase (Ar-AT) were purified and characterized from Lactococcus lactis subsp. lactis S3. The more abundant species, Ar-AT1, was purified over 2,200-fold with a 3% recovery. The molecular masses of Ar-AT1 were determined to be 42 kDa and 84 kDa by SDS-PAGE and gel filtration, respectively. The molecular masses of the less abundant species, Ar-AT2, were 42 kDa and 170 kDa, respectively. Both Ar-AT1 and Ar-AT2 have identical N-terminal sequences which indicates they are homodimeric and homotetrameric forms of the same enzyme. The Ar-ATs catalyze pyridoxal-5′-phosphate dependent transamination of Phe, Tyr, Trp, Leu and Met utilizing α-ketoglutarate as the amino acceptor. Km values of the two Ar-ATs for Trp, Tyr and Phe ranged from 0.65 to 2.43 mM. However, differences were observed in the pI and specific activities between the two Ar-ATs. The pI values of Ar-AT1 and Ar-AT2 were 4.63 and 3.93, respectively. The Vmax/Km ratios of Ar-AT2 for Trp, Tyr and Phe were three-fold greater than that of Ar-AT1, indicating that Ar-AT2 is more catalytically efficient on these amino acids than Ar-AT1.     

INHIBITION OF LISTERIA MONOCYTOGENES AND OTHER BACTERIA IN SPANISH SOFT CHEESE MADE WITH LACTOCOCCUS LACTIS SUBSP. DIACETYLACTIS

The inhibitory effects of a lactose-negative single-strain starter culture of Lactococcus lactis subsp. diacetylactis were evaluated in Spanish soft cheese (Queso fresco, pH 6.5) against Listeria monocytogenes, Escherichia coli O157:H7 , Enterobacter cloacae, Pseudomonas aeruginosa and Pseudomonas fluorescens. Queso Fresco made without starter culture and stored at 3 and 7C supported growth of all bacteria tested, with the exception of E. coli and P. aeruginosa which were unable to grow at 3C. When cheese was made with the starter culture and stored at 7C , L. monocytogenes, P. aeruginosa and E. coli did not grow, the growth of E. cloacae was delayed, and P. fluorescens grew uninhibited. In cheese stored at 3C, only P. fluorescens was able to grow.     

ISOLATION AND PARTIAL CHARACTERIZATION OF A NOVEL BACTERIOCIN PRODUCED BY LACTOCOCCUS LACTIS SSP. LACTIS MC38

This work presents the isolation and partial characterization of a new lactococcal bacteriocin produced by Lactococcus lactis ssp. lactis MC38. The bacteriocin demonstrated broad spectrum of inhibition activity against both pathogenic and food spoilage organisms, and various lactic acid bacteria. This antimicrobial substance appeared to be proteinaceous because its activity was completely inactivated by proteinase K and α‐chymotrypsin. It was heat and pH stable. The apparent molecular mass of the purified bacteriocin, determined by sodium dodecyl sulfate–polyacrylamide gel electrophoresis, was 8.0 kDa. The amino acid composition of the studied bacteriocin was found to be quite different from known lactococcal bacteriocins. The calculation of the number of amino acid residues in the bacteriocin molecule revealed that it contained 62 amino acids.     

乳酸乳球菌两组分食品级NICE系统载体的构建

乳酸菌食品级NICE系统是目前较理想的可控制蛋白质生产的食品级诱导表达系统。本实验构建的食品级表达载体pRNA48含α-aga食品级选择标记、θ型复制子和nisA启动子，与宿主菌L．hctis NZ9000共同构成乳酸乳球菌食品级NICE系统，可用于目的基因在乳酸乳球菌中高效诱导表达。     

Nisin对冷却猪肉冷藏保鲜效果的影响

研究Nisin对冷却猪肉保鲜效果的影响.研究中对比Nisin与山梨酸钾两种保鲜剂对冷却猪肉冷藏过程中6项鲜度指标(细菌总数、挥发性盐基氮、pH值、球蛋白、硫化氢以及感官指标)的变化情况.结果表明:Nisin在0.03 g/L～0.06 g/L浓度范围内可延长冷却猪肉货架期,其中以0.05 g/L Nisin保鲜液浸泡猪肉120 s保鲜效果最佳,货架期可延长6d,且与山梨酸钾保鲜剂(0.05 g/L)保鲜效果无明显差异.     

Nisin对酸奶发酵过程中后产酸抑制效果的研究

研究了Nisin对酸奶发酵过程中后产酸的抑制效果。实验结果表明：将Nisin添加到搅拌型酸牛奶中,贮存条件在20℃和4℃下都能有效地抑制酸牛奶的后酸化,而且酸牛奶的组织状态,感官质量良好。并确定了最适添加量为0.2g/kg,此时样品的感官质量优良,并且保持10^7cfu/mL的乳酸菌数量。     

棉浆粕制备条件对粘胶生产适用性的影响

本文论述了过低的棉短绒成熟度会引致粘胶生产过程压榨困难和过滤障碍。描述了在蒸球内设置中通管、来用重蒸轻漂、稳定漂白聚合度、以及漂后的除杂疏解等先进的工艺制造棉浆粕，有助于反应性能的提高，改善粘胶的过滤性能。但打浆时过分切断使纤维长度过短，会影响碱纤维素的压榨。采用干毯抄浆、浆粕存放（一段时间）均有助于浆粕水份均匀性的提高。