丁二酮乳酸乳球菌发酵对羊奶脂肪酸组成影响分析

为研究乳酸乳球菌乳酸亚种丁二酮变种(Lactococcus lactis ssp.Lactis biovar diacetylactis)在单菌发酵,或与嗜热链球菌(Streptococcus thermophilus)和保加利亚乳杆菌(Lactobacillus bulgaricus)混合发酵条件下对羊奶中脂肪酸含量影响情况,利用气相色谱法进行脂肪酸分析,结果表明:L.diacetylactis发酵显著提高了羊奶中、短链脂肪酸百分含量,降低了长链脂肪酸百分含量(p<0.05);L.diacetylactis接种量对发酵羊奶成品中脂肪酸组成影响不显著;L.diacetylactis与S.thermophilus、L.bulgaricus混合发酵羊奶中脂肪酸组成不受S.thermophilus、L.bulgaricus影响。因此,L.diacetylactis发酵适用于开发风味良好、营养合理的酮香型羊奶保健品。      

丁二酮乳酸乳球菌发酵对羊奶脂肪酸组成影响分析

为研究乳酸乳球菌乳酸亚种丁二酮变种(Lactococcus lactis ssp.Lactis biovar diacetylactis)在单菌发酵,或与嗜热链球菌(Streptococcus thermophilus)和保加利亚乳杆菌(Lactobacillus bulgaricus)混合发酵条件下对羊奶中脂肪酸含量影响情况,利用气相色谱法进行脂肪酸分析,结果表明:L.diacetylactis发酵显著提高了羊奶中、短链脂肪酸百分含量,降低了长链脂肪酸百分含量(p<0.05);L.diacetylactis接种量对发酵羊奶成品中脂肪酸组成影响不显著;L.diacetylactis与S.thermophilus、L.bulgaricus混合发酵羊奶中脂肪酸组成不受S.thermophilus、L.bulgaricus影响。因此,L.diacetylactis发酵适用于开发风味良好、营养合理的酮香型羊奶保健品。     

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。     

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...     

德氏乳杆菌保加利亚亚种发酵乳风味成分分析

本实验采用同时蒸馏萃取- 气谱- 质谱(SDE-GC-MS)联用技术对5 株德氏乳杆菌保加利亚亚种L.b-01、L.b-3、L.b-MYC、L.b-SP1.1 和L.b-M01A 发酵乳中风味物质进行了定性和定量测定,经分析分别有13、19、11、9、12 种成分为发酵乳的风味物质,共涉及酸类化合物、酯类化合物、醇类化合物、羰基化合物、芳环和杂环化合物6 大类、22 种物质。除L.b-M01A 菌产乙醇、乙酸含量较高外,其他各菌株间未发现存在明显的代谢差异。     

乳酸乳球菌乳脂亚种BTQY-112增殖培养基的优化

对乳酸乳球菌乳脂亚种BTQY-112增殖培养基进行优化研究。经试验确定乳酸乳球菌乳脂亚种BTQY-112最适培养基为:葡萄糖为5 g/L,乳糖为5 g/L,酪蛋白胨3.3 g/L,大豆蛋白胨3.3 g/L,鱼蛋白胨3.3 g/L,β-甘油磷酸二钠28.5 g/L,Tween-80 0.5 g/L,七水硫酸镁0.25 g/L,乙酸钠1.55 g/L,K2HPO40.83 g/L,柠檬酸钠0.62 g/L,抗坏血酸钠1.5 g/L。在此增殖培养基中经30℃,14 h培养活菌数提高了4.3倍。     

唾液链球菌嗜热亚种发酵乳风味成分分析

本实验使用同时蒸馏萃取-气谱-质谱(SDE-GC-MS)技术对5株唾液链球菌嗜热亚种S.t-9、S.t-17YA、S.t-1703CA、S.t-1703D和S.t-03发酵乳中风味物质进行了定性及定量分析,分别鉴定出24种、20种、13种、20种、21种风味物质,共涉及6大类:酸类化合物、酯类化合物、醇类化合物、羰基化合物、芳环和杂环化合物,35种物质.另外,5株菌代谢主要风味物质2,3.丁二酮的能力大小为:S.t-1703D>S.t-1703CA>S.t-17YA>S.t-03>S.t-9,除S.t-9菌代谢2,3-丁二酮量较低外,其它4种菌代谢丁二酮的能力差异不大.     

乳酸乳球菌乳酸亚种IMAU11823全基因组测序及胞外多糖基因簇分析

目的:乳酸乳球菌乳酸亚种IMAU11823是从内蒙古锡林郭勒盟自然发酵乳制品嚼口中分离得到的1株具有优良发酵特性且高产胞外多糖的乳酸菌.为探究其产胞外多糖的作用机制,对其进行全基因组测序并解析基因组序列信息.方法:使用PacBio SMRT三代测序技术对该菌株进行全基因组测序,采用生物信息学方法对其进行序列组装、基因预...     

Effect of alpha-acetolactate decarboxylase inactivation on alpha-acetolactate and diacetyl production by Lactococcus lactis subsp. lactis biovar diacetylactis

Strains of Lactococcus lactis subsp. lactis biovar diacetylactis deficient in alpha-acetolactate decarboxylase produce alpha-acetolactate. This unstable compound is a precursor of acetoin and an aromatic compound, diacetyl. Following random mutagenesis of strain CNRZ 483, alpha-acetolactate decarboxylase-negative mutant 483 M1 was selected. When grown in milk, its growth and acidification characteristics were similar to those of the parental strain. In anaerobic conditions, the parental strain produced 2.10 mM acetoin and less than 0.05 mM diacetyl. The mutant accumulated up to 2.11 mM alpha-acetolactate, which spontaneously degraded to acetoin and diacetyl. After 24 h of culture, the alpha-acetolactate concentration was only 0.49 mM and the acetoin and diacetyl concentrations reached 1.50 mM and 0.26 mM, respectively. Diacetyl production by both strains increased in aerobic conditions, as well as when citrate was added. In contrast to cultures of the parental strain, however, diacetyl and acetoin concentrations in mutant cultures continued to increase without reaching a plateau. The results also showed that diacetyl production by wild type L. lactis subsp. lactis biovar diacetylactis strains cannot be explained uniquely by the spontaneous decarboxylation of the alpha-acetolactate produced in the culture medium.     

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%。      

Growth characteristics of Candida kefyr and two strains of Lactococcus lactis subsp. lactis isolated from Zimbabwean naturally fermented milk.

Lactic acid bacteria (LAB) and yeasts constitute part of the microflora in Zimbabwean traditional fermented cows' milk, amasi. The present study was carried out to investigate the growth characteristics of Candida kefyr 23, Lactococcus lactis subsp. lactis biovar. diacetylactis C1 and L. lactis subsp. lactis Lc261, previously isolated from amasi, in ultrahigh temperature (UHT)-treated cows' milk. The strains were inoculated into the UHT milk as both single and yeast     

Improved viability of bifidobacteria in fermented milk by cocultivation with Lactococcus lactis subspecies lactis

The poor survival of probiotic bacteria in commercial yogurts may limit their potential to exert health benefits in humans. The objective was to improve the survival of bifidobacteria in fermented milk. Cocultivation with some strains of Lactococcus lactis ssp. lactis improved the survival of bifidobacteria in fermented milk during refrigerated storage. Studies on one strain, Lc. lactis ssp. lactis MCC866, showed that the concentrations of dissolved oxygen were kept lower in the cocultivated fermented milk during storage compared with monocultured Bifidobacterium longum BB536 or samples cocultured with another noneffective Lc. lactis ssp. lactis strain. Degradation of genomic DNA was suppressed in the cocultivating system with Lc. lactis ssp. lactis MCC866. Several genes that participated in protection from active oxygen species (e.g., genes coding for alkyl hydroperoxide reductase and Fe²⁺ transport system) were expressed at higher levels during refrigerated storage in Lc. lactis ssp. lactis MCC 866 compared with another noneffective Lc. lactis ssp. lactis strain. Concentration of free iron ion was also lower in supernatants of fermented milk cocultivated with B. longum BB536 and Lc. lactis ssp. lactis MCC866. These results suggest that Lc. lactis ssp. lactis MCC 866 is potentially superior in reducing oxygen damage and consequently improves the survival of bifidobacteria in the cocultivating system. This cocultivation system is of industrial interest for producing fermented milk containing viable bifidobacteria with long shelf life.     

乳酸乳球菌富硒及其硒多糖抗氧化活性研究

对乳酸乳球菌富硒工艺进行优化以及对其最优条件下提取的硒多糖抗氧化活性研究,结果表明:接种量、培养时间、亚硒酸钠浓度是影响乳酸乳球菌富硒量的主要因素;当接种量8%,培养时间24h,亚硒酸钠浓度14μg/mL,温度37℃,pH6.6时,乳酸乳球菌的有机硒转化率为59.87%。当最优条件下提取的硒多糖浓度达2mg/mL时,硒多糖对羟自由基和超氧阴离子的清除率为78%和59%,较同等条件下多糖的清除率分别提高了19%和18%。      

Substrate specificity of a tripeptidase as a metalloenzyme purified from Lactococcus lactis subsp. lactis biovar. diacetylactis ATCC 13675

The peptidase purified to homogeneity from Lactococcus lactis subsp. lactis biovar. diacetylactis ATCC 13675 was considered to be an aminotripeptidase (EC 3.4.11.4) from the results of substrate specificity. The K(m) value showed a tendency to decrease with the number of alanine residues, but to increase with the number of glycine residues in the substrate tripeptide. The effects of divalent metal ions on enzyme activity were considerably different depending on the tripepride used as a substrate. In the case of Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+, there was apparent correlation between enzyme activities observed in the presence of metal ions and following metal ion replacement. The Zn2+-replaced enzyme showed almost the same K(m) and k(cat) values as the native enzyme, suggesting the enzyme to be a zinc metallopeptidase. The K(m) of the divalent metal-replaced enzyme increased in the order of Co2+, Zn2+, and Mn2+. As a result of replacement with Co2+ an enzyme having 2.3-fold higher activity compared to the native enzyme for GGF as a substrate was obtained. Thus, the change in substrate specificity observed following metal replacement may suggest a highly specific interaction between the enzyme, metal and substrate, leading to the activity expression and stability of the tripeptidase.     

乳酸乳球菌发酵液中乳链菌肽的分离纯化

对乳酸乳球菌乳酸亚种SQ80随pH的改变吸附乳链菌肽的规律进行了研究，pH6．5时吸附率达91．5％，pH3以下吸附率为0。通过调整pH，使乳酸乳球菌选择性地吸附、释放乳链菌肽，达到了较好的分离纯化效果，HPLC检测显示单一尖峰，乳链菌肽回收率58．2％，纯化倍数75。