自然发酵牛乳中乳酸菌和酵母菌的活菌动态变化

构建三批次各100 kg牛乳自然发酵体系,通过分析乳酸菌和酵母菌的活菌动态变化,对两者间的相互作用进行研究。结果表明,在（20±1）℃的自然发酵温度下,持续发酵56 h,pH值下降至4.6～5.0,发酵牛乳逐渐分层并形成上层奶嚼口和下层凝乳。连续三个批次发酵牛乳中奶嚼口和凝乳的乳酸菌平均活菌数分别为（12.02±1.21）lg（CFU/mL）和（11.54±1.30）lg（CFU/mL）,差异不显著（P＞0.05）;而凝乳中酵母菌平均活菌数[（6.39±0.60）lg（CFU/mL）]显著低于奶嚼口[（4.56±0.30）lg（CFU/mL）]（P＜0.05）。活菌动态变化表明,在牛乳自然发酵过程中,乳酸菌的生长具有延迟期、对数期、稳定期三个典型阶段,而酵母菌没有明显的对数期,随着乳酸菌的生长反而抑制酵母菌的生长。     

蒙古族传统奶嚼口的微生物组成分析

通过对蒙古族传统奶嚼口进行微生物组成分析，以期为地方标准制定及工业化产品开发提供理论依据和有益借鉴。采用纯培养方法对奶嚼口样品中乳酸菌、双歧杆菌和大肠杆菌培养计数，并通过16S rDNA基因序列分析对其进行种属鉴定。结果显示，奶嚼口样品中乳酸菌活菌数为（7.91~8.69） lg（CFU/mL），双歧杆菌活菌数为（4.09~6.64） lg（CFU/mL），大肠杆菌活菌数为（0~5.45） lg（CFU/mL）；样品中菌种分属于5个属，其中优势菌株为粪肠球菌（Enterococcus faecalis 34.55%）、植物乳杆菌（Lactobacillus plantarum 25.45%）和乳酸乳球菌（Lactococcus lactis 16.36%）。研究表明，蒙古族传统奶嚼口含有丰富的乳酸菌和双歧杆菌资源，其中的污染指标菌（大肠杆菌）是工业化生产的掣肘所在，而蒙古族传统奶嚼口具有酸性高脂的天然属性，为潜在功能益生菌的开发提供了丰富的菌种资源。     

酸白菜腌制过程中优势乳酸菌及菌群演替规律研究

以陕西杨凌地区大白菜为原料,切碎,添加2.5%食盐,在22 ℃进行半厌氧自然发酵酸泡菜。发酵过程中在不同时间取泡菜液,测定泡菜pH值、乳酸菌落和菌落总数变化,分离鉴定优势乳酸菌株,检测酸白菜微生物多样性,探究酸白菜腌制过程中菌群的演替变化规律。结果表明:泡菜自然发酵,从第0天到第7天,pH值从初始的6.0降到4.2,乳酸菌数由4.65 lg(CFU/mL)增至7.86 lg(CFU/mL),菌落总数由9.11 lg(CFU/mL)减至8.65 lg(CFU/mL)。在不同发酵阶段共分离鉴定出27株乳酸菌,分别为10株明串珠菌,7株魏斯氏菌,4株乳酸乳球菌,4株弯曲乳杆菌和2株戊糖片球菌。泡菜发酵起始优势乳酸菌种属为魏斯氏菌,发酵中期优势乳酸菌逐渐变成乳酸乳球菌,肠膜明串珠菌演替成优势乳酸菌。整个泡菜发酵阶段异型乳酸发酵菌种占据主导地位,发酵中、后期(5 d后)同型乳酸发酵菌种参与泡菜发酵。     

甘南牧区犏牛酸奶中优良乳酸菌的分离与鉴定

从甘南牧区采集的犏牛酸奶中分离得到76 株乳酸菌。筛选得到3 株凝乳快速、产酸力强、凝乳质地优良的乳酸菌菌株,包括1 株球菌和2 株杆菌。采用16S rRNA基因序列比对分析,鉴定3 株乳酸菌分别是屎肠球菌（Enterococcus faecium）、德氏乳杆菌（Lactobacillus delbrueckii）和发酵乳杆菌（Lactobacillus fermentum）。通过球杆菌混合发酵实验,结果表明混合菌株发酵的产酸速率比单菌株发酵明显加快,且后酸化程度较弱,其感官质量也明显优于单菌发酵。     

广西生榨米粉中益生乳酸菌的筛选及鉴定

通过革兰氏染色、过氧化氢酶试验、溶血性试验、耐酸、耐胆盐试验及体外抗氧化能力测定从广西本地传统发酵食品生榨米粉中筛选优良益生乳酸菌，对其生长情况及产酸性能进行测定，并通过分子生物学技术对其进行鉴定。结果表明，共分离得到146株γ-溶血乳酸菌，其中22株乳酸菌对pH 2.0和0.3%胆盐均具有良好耐受性，且乳酸菌PM20、PM22、FD13及PM44的综合体外抗氧化能力较好。4株菌株的生长及产酸趋势一致，其中菌株PM44的生长速度和产酸能力最强。经鉴定菌株PM20、PM22、FD13均为发酵乳杆菌（Lactobacillus fermentum），菌株PM44为乳酸片球菌（Pediococcus acidilactici）。     

甘肃牧区传统发酵乳制品中优良乳酸菌的分离筛选

从甘肃牧区传统发酵乳制品中分离筛选适合发酵乳生产的乳酸菌,对分离纯化的乳酸菌进行了发酵性能检测,筛选出产酸快、发酵活力高、凝乳时间短、后酸化能力弱、遗传性状稳定的菌株。筛选的6株菌株单菌发酵牛乳,均在6.5 h内凝乳,发酵乳酸度＞70 °T,乳酸菌活菌数＞1×108 CFU/mL,发酵乳组织状态、滋味、气味等感官指标良好,可作为生产发酵乳的优良乳酸菌菌种进行开发利用。     

内蒙古优质传统酸牛奶中乳球菌的发酵特性研究

通过酸度测定,从内蒙古优质传统酸牛奶中分离的11株乳球菌中筛选出7株发酵酸乳凝乳时间短和凝乳状态好的乳球菌,进一步研究这7株乳球菌在乳中的发酵特性。测定菌株在凝乳前的产酸特性、冷藏24 h后的质构特性及4℃冷藏期间的产酸特性及活菌数变化。结果表明:菌株KLDS 4.1109和KLDS 4.1110产酸能力、后酸化能力及质构特性最好,且其在4℃冷藏期间活菌数都能维持在106cfu/mL以上。可见菌株KLDS 4.1109和KLDS 4.1110能成为新型发酵菌种,具有很大的开发潜力。     

高产γ-氨基丁酸植物乳杆菌的筛选、鉴定及益生特性

从东北酸菜和韩国泡菜中筛选高产γ-氨基丁酸的植物乳杆菌菌株,对其测序鉴定乳酸菌种类,并深入研究该菌株的益生特性。结果表明：通过16S rDNA 测序鉴定该菌株为植物乳杆菌,命名为Lactobacillus plantarum Lp3。该菌株有良好的生长和产酸能力,接种2～12 h 生长较快进入对数期,接种0～6 h 快速产酸。益生特性表明：L.plantarum Lp3 菌株对大肠杆菌、沙门氏菌、金黄色葡萄球菌均有较好的抑制效果,对沙门氏菌抑菌圈直径达32.27 mm。当胆盐浓度为0.5%和pH 值为2.0 时,L.plantarum Lp3 菌株活菌数分别为7.12 lg（CFU/mL）和7.29 lg（CFU/mL）,说明其具有良好的耐胆盐及耐酸能力。同时,L.plantarum Lp3 菌株在胃肠道中表现出很好的生存能力,对常用的红霉素、氯霉素和四环素等抗生素具有一定的敏感性。     

降胆固醇乳酸菌的筛选、鉴定与益生特性评价

目的：从婴儿粪便和发酵食品中筛选具有高效降胆固醇能力且益生特性优异的乳酸菌。方法：从20份婴儿粪便、8份传统发酵泡菜和4份金华火腿样品中初步筛选到乳酸菌102株,采用气相色谱法测定供试菌株的降胆固醇能力,菌株ZY08和I631的降胆固醇能力显著高于（P<0.05）标准菌株（ATCC 43121）;采用16S rDNA测序对这2株乳酸菌进行鉴定,评价菌株的酸耐受性、胆盐耐受能力、抗生素敏感性及抗菌活性。结果：筛选得到2株高效降胆固醇乳酸菌：植物乳杆菌ZY08和发酵乳杆菌I631,胆固醇降低率分别为67.45%和63.19%。在pH 1.5和pH 3.0的条件下培养6 h,菌株ZY08和I631的活菌数均大于6 lg（CFU/mL）。2株菌对3,5及1.0 g/L胆盐具有一定的耐受性,胆盐耐受能力均在80%以上（胆盐含量为3 g/L）;对常见的8种抗生素（青霉素、氨苄青霉素、头孢唑林、丁胺卡那、庆大霉素、红霉素、复方新诺明、氯霉素）都不具备耐药性,对人体健康不存在潜在威胁;2株菌的代谢产物对4种肠道致病菌（金黄色葡萄球菌、单核细胞增生李斯特菌、大肠杆菌O157∶H7、鼠伤寒沙门氏菌）具有一定的抑制作用。结论：获得具有高效降胆固醇能力的植物乳杆菌ZY08和发酵乳杆菌I631,为功能性乳制品的开发提供菌株来源。     

乳酸菌蛋白降解及产香能力分析

研究了分离自新疆酸奶疙瘩中6株乳酸菌在37℃下蛋白质降解和产香能力。结果表明,6株乳酸菌稳定期活菌数均在108CFU/mL以上,且凝乳细腻,具有良好的组织状态。各菌株发酵性能有差异,干酪乳杆菌、瑞士乳杆菌、乳脂乳球菌3株菌发酵性能较植物乳杆菌、嗜热链球菌、保加利亚乳杆菌发酵性能优,可用于不同风味和功能的发酵乳制品生产。其中,干酪乳杆菌具有良好的蛋白水解力,发酵15h,酪氨酸含量为594.33μg/mL;乳脂乳球菌产香性能好,发酵24h,丁二酮含量为12.32μg/mL、乙醛含量为59.27μg/mL,与其他菌株具有显著差异;瑞士乳杆菌具有强的产酸、产黏特性,发酵24h,酸度达159.76°T,黏度值1 389mPa·s。     

川西高原发酵牦牛乳中降解亚硝酸盐乳酸菌的筛选与耐受性研究

以川西高原发酵牦牛乳中分离出的195株乳酸菌为研究对象,采用比色法测定其亚硝酸盐降解能力,从中筛选出亚硝酸盐降解能力极强的菌株。将这些优势菌株分别在人工胃液、人工肠液、胆盐和高盐4个模拟人工胃肠道消化环境中进行培养,测其耐受力。结果表明:这195株乳酸菌亚硝酸盐降解率范围为35.79%~96.51%,其中降解率在80%~90%的菌株占54.87%,仅有1.54%的菌株亚硝酸盐降解率在50%以下,有3株亚硝酸盐降解能力极强的菌株(降解率大于95%)。这3株菌在人工胃液中的活菌数随培养时间的延长而减少,培养3 h后,菌株5、26、150在pH5.5时的活菌数分别为3.7、3.6、4.1×108 CFU/mL;在人工肠液中培养4 h后,菌株5、26、150的活菌数分别为4.3、6.8、5.3×108 CFU/mL;在不同胆盐梯度的培养基中培养24 h后,3株菌的活菌数随胆盐浓度增大而减少,且均保持在108 CFU/mL以上;在高盐环境中培养24 h后的活菌数随盐质量浓度的增加而降低,活菌数均在108 CFU/mL以上。结论:川西高原发酵牦牛乳中分离出的195株乳酸菌降解亚硝酸盐的能力存在较大差异,其中降解亚硝酸盐能力极强的菌株对体外模拟消化环境具有较好的耐受力,为其在医药,食品和生物领域的应用提供了理论依据。     

发酵酸菜来源乳酸菌的益生特性及其在发酵乳中的应用

通过pH值、胆盐耐受性实验从发酵酸菜中筛选性能优良的益生乳酸菌株,经16S rRNA序列分析鉴定得4 株植物乳杆菌A44、B51、B54、C53和2 株戊糖乳杆菌A16、B72。经疏水、黏附、自凝聚和溶血能力实验评价6 株乳酸菌的益生特性,其中植物乳杆菌A44对氯仿和二甲苯的疏水性均大于80%,对Caco-2细胞的黏附率为13.57%,放置5 h的自凝聚率超过60%,与其他菌株相比具有更好的益生特性且无溶血活性。因此选用植物乳杆菌A44进一步研究其在发酵乳中的功能特性,结果表明：植物乳杆菌A44作为辅助发酵剂添加后对4 ℃贮藏7 d期间发酵乳pH值、滴定酸度和持水性均无显著影响（P＞0.05）,但是可以显著提高发酵乳的活菌数和黏度（P＜0.05）,活菌数达到8.45（lg（CFU/mL））。本研究筛选得到的植物乳杆菌A44是一株性能优良的益生乳酸菌,具有作为发酵乳益生菌辅助发酵剂的潜在应用前景。     

渗透压胁迫对耐盐乳酸菌发酵特性的影响

采用传统分离培养法从新疆伊犁昭苏县土壤样品中分离筛选耐盐乳酸菌,通过形态观察及分子生物学技术对其进行鉴定,并探究高盐胁迫（7%、8% NaCl）下其生长速率、产酸性能、耐酸、耐胆盐胁迫能力的变化。结果表明,筛选得到4株耐盐乳酸菌,其中菌株a、b、c被鉴定为海氏肠球菌（Enterococcus hirae）,菌株d被鉴定为植物乳杆菌（Lactobacillus plantarum）。在高盐胁迫（7%、8% NaCl）下,L. plantarum d的生长特性、产酸及耐酸性能最好,但耐胆盐能力最差,E. hirae a、b、c的耐胆盐胁迫能力更佳;在10%和12%的NaCl含量下胁迫3 h,4株菌的存活率均能维持在36%以上,其中E. hirae b的耐盐能力最佳,存活率最高。     

贵州泡菜中乳酸菌的分离鉴定及其在泡菜发酵中的应用

以贵州遵义市采集的不同家庭自制的11份发酵泡菜制品为材料,从中筛选产酸量较高的乳酸菌,通过形态观察、生理生化试验及分子生物学技术对其进行鉴定,并对其耐酸、耐胆盐、耐盐及抑菌性能进行测定,筛选性能优良的乳酸菌,最后将其应用到发酵泡菜中。结果表明,筛选得到11株产酸量较高的乳酸菌,产酸量均＞1.89 g/L,经鉴定5株为植物乳杆菌（Lactobacillus plantarum）,6株为副植物乳杆菌（Lactobacillus paraplantarum）,其中菌株A50f7和A50b9的耐酸、耐胆盐、耐盐及抑菌性能优良。人工接种这两株乳酸菌发酵泡菜,能显著缩短泡菜发酵周期,改善泡菜的品质。     

新疆传统乳品中产胞外多糖乳酸菌的筛选及益生特性的研究

以新疆塔城地区酸奶、酸马奶、鲜马奶样品为研究对象,采用传统的分离方法对样品中的乳酸菌进行分离,通过16S rRNA分析样品中微生物多样性,在优势菌株中通过苯酚-硫酸法筛选出高产胞外多糖的乳酸菌,测定菌株潜在的益生特性。结果显示,3份酸奶、4份酸马奶和3份鲜马奶共10份样品中分离鉴定出147株乳酸菌,优势菌株为屎肠球菌（Enterococcus faecium）、发酵乳杆菌（Lactobacillus fermentum）和植物乳杆菌（Lactobacillus plantarum）。筛选出3株高产胞外多糖的植物乳杆菌（菌株1-3,1-6,4-1）。潜在益生特性试验结果显示,3株菌均表现出一定的益生特性,其中菌株1-3较其他菌株有较强的肠道定植、降胆固醇能力和胆盐耐受性,其可作为潜在益生菌应用于功能性产品的开发。     

Screening of lactic acid bacteria for bile salt hydrolase activity

Bile salt hydrolysis is an important metabolic reaction in the bile salt metabolism of mammals. This reaction has a facilitating effect for bile salt excretion but can also be involved in various illnesses. In recent years interest has increased to use bile salt hydrolysis to influence the cholesterol metabolism of humans and farm animals. To understand the distribution and range of bile salt hydrolase activity in lactic acid bacteria, we screened more than 300 strains of the genera Bifidobacterium and Lactobacillus and the species Lactococcus lactis, Leuconostoc mesenteroides, and Streptococcus thermophilus. Results obtained for 273 strains showed that bile salt hydrolase activity is common in Bifidobacterium and Lactobacillus but absent in L. lactis, Leu. mesenteroides, and S. thermophilus. Nearly all bifidobacteria species and strains have bile salt hydrolase activity, whereas this activity can only be found in selected species of lactobacilli. A strong correlation can be observed between the habitat of a genus or species and the presence of bile salt hydrolase activity. Most often bile salt hydrolase activity is found in strains that have been isolated from the intestines or from feces from mammals--an environment rich in conjugated and unconjugated bile acids. Strains and species from other habitats like milk or vegetables--environments from which bile salts are absent--do normally not have bile salt hydrolase activity. In two independent assays, we established that bile salt hydrolase activity in bifidobacteria is, in general, much higher than in lactobacilli.     

Characterization of the lactic acid bacteria in ewe's milk and cheese from northwest Argentina

Indigenous lactic acid bacteria in ewe's milk and artisanal cheese were studied in four samples of fresh raw milk and four 1-month-old cheeses from the provinces of northwest Argentina. Mean growth counts on M17, MRS, and MSE agar media did not show significant differences (P < 0.05) in raw milk and cheeses. Isolates of lactic acid bacteria from milk were identified as Enterococcus (48%), lactococci (14%), leuconostocs (8%), and lactobacilli (30%). All lactococci were identified as Lactococcus lactis (subsp. lactis and subsp. cremoris). Lactobacilli were identified as Lactobacillus plantarum (92%) and Lactobacillus acidophilus (8%). Enterococci (59%) and lactobacilli (41%) were isolated from cheeses. L. plantarum (93%), L. acidophilus (5%), and Lactobacillus casei (2%) were most frequently isolated. L. lactis subsp. lactis biovar diacetylactis strains were considered as fast acid producers. L. lactis subsp. cremoris strains were slow acid producers. L. plantarum and L. casei strains identified from the cheeses showed slow acid production. The majority of the lactobacilli and Lactococcus lactis strains utilized citrate and produced diacetyl and acetoin in milk. Enzyme activities (API-ZYM tests) of lactococci were low, but activities of L. plantarum strains were considerably higher. The predominance of L. plantarum in artisanal cheese is probably important in the ripening of these cheeses due to their physiological and biochemical characteristics.     

Acid, bile, and heat tolerance of free and microencapsulated probiotic bacteria

ABSTRACT:  Eight strains of probiotic bacteria, including Lactobacillus rhamnosus , Bifidobacterium longum, L. salivarius, L. plantarum , L. acidophilus , L. paracasei , B. lactis type Bl-O4, and B. lactis type Bi-07, were studied for their acid, bile, and heat tolerance. Microencapsulation in alginate matrix was used to enhance survival of the bacteria in acid and bile as well as a brief exposure to heat. Free probiotic organisms were used as a control. The acid tolerance of probiotic organisms was tested using HCl in MRS broth over a 2-h incubation period. Bile tolerance was tested using 2 types of bile salts, oxgall and taurocholic acid, over an 8-h incubation period. Heat tolerance was tested by exposing the probiotic organisms to 65 °C for up to 1 h. Results indicated microencapsulated probiotic bacteria survived better ( P < 0.05) than free probiotic bacteria in MRS containing HCl. When free probiotic bacteria were exposed to oxgall, viability was reduced by 6.51-log CFU/mL, whereas only 3.36-log CFU/mL was lost in microencapsulated strains. At 30 min of heat treatment, microencapsulated probiotic bacteria survived with an average loss of only 4.17-log CFU/mL, compared to 6.74-log CFU/mL loss with free probiotic bacteria. However, after 1 h of heating both free and microencapsulated probiotic strains showed similar losses in viability. Overall microencapsulation improved the survival of probiotic bacteria when exposed to acidic conditions, bile salts, and mild heat treatment.