Antibacterial activity and cholesterol assimilation of lactic acid bacteria isolated from traditional Iranian dairy products

In this study, lactic acid bacteria were isolated from ewe milk, traditional yoghurt and sour buttermilk samples collected from different areas of Azarbayjan-e-sharqi in Iran. All the isolates were screened for their ability to produce bacteriocin like inhibitory substances (BLIS) by studying their inhibitory action against pathogens like Listeria monocytogenes, Salmonella enteritidis and Staphylococcus aureus, after eliminating the effect of organic acids and hydrogen peroxide. According to results, four of the isolates identified as Lactobacillus brevis, Lactobacillus pentosus, Pedoicoccus acidilactici and Lactobacillus paracasei were unaffected by the action of pH neutralization and hydrogen peroxide and showed inhibitory action against the tested pathogens. The inhibitory activities demonstrated by these isolates were completely inhibited in the presence of proteolytic enzymes.     

Identification and characterisation of lactic acid bacteria isolated from traditional Urfa cheese

In this study, characterisation of dominant strains of lactic flora in traditional Urfa cheese made from sheep's milk was performed using biochemical, phenotypic and genotypic methods. According to the results obtained, the percentage distributions of the lactic acid bacteria isolated were as follows: 48.95% Enterococcus spp., 40.55% Lactococcus spp., 9.10% Lactobacillus spp., 0.69% Streptococcus spp. and 0.69% Leuconostoc spp. The majority of lactococcal isolates showed an atypical phenotype of growing in the presence of 6.5% NaCl. Acidification and bacteriocin production were also determined for each isolate. Four strains showed bacteriocin activity.     

乳酸菌及其代谢产物在乳制品保鲜中的应用

乳酸菌及其某些代谢产物,以其天然、强抗菌性及安全可靠等优势,已逐步应用于食品保鲜中。对乳酸菌用于乳制品保鲜的类型、代谢产物抗菌机制以及应用进行了综述,为研究开发新型食品保鲜剂提供依据。     

Folate‐producing lactic acid bacteria from cow’s milk with probiotic characteristics

The probiotic potential of newly isolated lactic acid bacteria from cow’s milk was analysed and the efficacy of the selected isolates to produce folic acid was determined by microbiological assay. Two isolates, CM 22 and CM 28 were selected for folate production in skim milk medium and the net folate yield was 12.5 ng and 14.2 ng/mL respectively. The two isolates (CM 22 and CM 28) showed more than 98% similarity to Lactococcus subsp. cremoris and Lactococcus lactis subsp. lactis respectively by 16S rRNA sequencing.     

自然发酵肉制品中乳酸菌的分离及特性研究

以MRS和改良TJA(改良番茄汁琼脂培养基)培养基为基础培养基,从自然发酵肉品中分离得到8个菌株,其中4株为乳酸菌,3株为杆菌,1株为球状菌。进一步测试表明:4株乳酸菌在30℃培养时,生长最好;在pH3.5～4.0时生长良好;4株乳酸菌在10%NaCl的环境中均能生长,其中以2%～6%的NaCl浓度内生长最适宜;属兼性厌氧菌;对大肠杆菌产生一定的抑制作用。分离出的4株乳酸菌均适宜作为发酵肉制品的发酵剂。     

新疆乳品中乳酸菌的多样性及耐药性分析

从新疆北部地区采集的样品中分离出103株乳酸菌并进行生理生化表型鉴定,对这些乳酸菌进行16S rRNA基因序列测序,构建系统发育树发现分离的乳酸菌主要为5个属分别为乳杆菌属、肠球菌属、乳球菌属、魏斯式菌属、明串珠菌属。采用纸片扩散法（K-B）研究不同属中不同乳酸菌对8种常见抗生素的耐药性分析。耐药性研究表明,分别有6株对链霉素、新霉素有耐药性,5株对红霉素有耐药性,7株对卡那霉素有耐药性,8株全部对萘啶酸具有耐药性,4株对万古霉素、四环素具有耐药性,2株对头孢唑肟存在耐药性。     

乳酸菌对发酵乳制品风味形成的影响

乳酸菌对发酵乳制品风味有决定性影响,发酵乳制品的风味物质主要是乳酸菌利用脂肪、碳水化合物和蛋白质等物质产生的。文章对乳酸菌代谢脂肪、糖、柠檬酸和氨基酸产生芳香物质的机理进行了综述。     

乳酸菌及其发酵乳制品的发展趋势

综述了乳酸菌的生物学特性、功能及用于乳制品发酵生产的乳酸菌种类。概述了发酵乳制品的种类、生产流程、特点、功能及其发展趋势，以及乳酸菌发酵乳制品保健功能、风味物质及其生产技术的发展趋势。     

Succession of dominant and antagonistic lactic acid bacteria in fermented cucumber: insights from a PCR-based approach

The goal of the investigation was to study the succession of major groups of lactic acid bacteria (LAB) and their antagonism in salt-fermented cucumber using PCR. In a direct detection method as well as a short enrichment process, PCR enabled detection of Leuconostoc and Lactobacillus during early hours of fermentation. Subsequently, Lactobacillus and Pediococcus emerged as the dominant genera. Nucleic acid sequence of culture-independent clones confirmed the detection of Pediococcus as a dominant genera emerging during late stages of fermentation. PCR also revealed time-dependent emergence of mesentericin, pediocin and plantaricin A producers and accounted for the LAB succession in the fermenting samples. A total of 328 LAB isolates were obtained collectively from 30 cucumber samples, of which PCR could identify an overwhelming 186 Lactobacillus isolates followed by 113 Pediococcus and 29 Leuconostoc isolates, respectively. Based on antimicrobial assay against target strain Leuconostoc mesenteroides NRRL B640, 28% of the LAB were bacteriocin producers, of which pediocin producers were substantial, followed by plantaricin A and mesentericin producers. The bacteriocins elaborated by the isolates were active against a large number of Gram-positive target LAB strains and pathogenic bacteria including Bacillus cereus, Enterobacter aerogenes, Enterococcus faecalis, Escherichia coli, Listeria monocytogenes and Staphylococcus aureus.     

Occurrence and role of lactic acid bacteria in seafood products

Lactic acid bacteria (LAB) in fish flesh has long been disregarded because the high post-mortem pH, the low percentage of sugars, the high content of low molecular weight nitrogenous molecules and the low temperature of temperate waters favor the rapid growth of pH-sensitive psychrotolerant marine Gram-negative bacteria like Pseudomonas, Shewanella and Photobacterium. In seafood packed in both vacuum (VP) and modified atmosphere (MAP) packaging commonly CO₂ enriched, the growth of the Gram-negative aerobic bacteria group (predominantly pseudomonads) is effectively inhibited and the number reached by LAB during storage is higher than that achieved in air but always several log units lower than the trimethylamine oxide (TMA-O) reducing and CO₂-resistant organisms (Shewanella putrefaciens and Photobacterium phosphoreum). Accordingly, LAB are not of much concern in seafood neither aerobically stored nor VP and MAP. However, they may acquire great relevance in lightly preserved fish products (LPFP), including those VP or MAP. Fresh fish presents a very high water activity (aw) value (0.99). However, aw is reduced to about 0.96 when salt (typically 6% WP) is added to the product. As a result, aerobic Gram-negative bacteria are inhibited, which allows the growth of other organisms more resistant to reduced aw, i.e. LAB, and then they may acquire a central role in the microbial events occurring in the product. Changes in consumers’ habits have led to an increase of convenient LPFP with a relative long shelf-life (at least 3 weeks) which, on the other hand, may constitute a serious problem from a safety perspective since Listeria monocytogenes and sometimes Clostridium botulinum (mainly type E) may able to grow. In any case the LAB function in marine products is complex, depending on species, strains, interaction with other bacteria and the food matrix. They may have no particular effect or they may be responsible for spoilage and, in certain cases, they may even exert a bioprotective effect in relation to undesirable bacteria. The bioprotective potential of endogenous LAB in relation to pathogens and spoiling bacteria has often been highlighted. However, the technology is still in its infancy compared with foods dairy and meat products in which either the carbohydrate content (dairy products) or sugar and salt added (meat products) favor the acidification by LAB that enable a natural preservation of the product. Successful studies on LAB as probiotic for fish intensify, but this potential is still to be explored for human. Although not usual, some applications of LAB for fermentation of marine products and by-products are described.     

豆腐酸浆老汤中产酸菌的分离筛选与鉴定

利用MRS选择性培养基,从分别采自山东邹平、陕西榆林、河北涞源、云南石屏、云南建水及云南元阳的6份酸浆老汤中分离纯化出12种菌落形态不一样的乳酸菌,分别采用MC改良培养基和发酵黄浆水p H及产酸量的监测对12种菌进行初筛及复筛,筛选出一株产酸较快、较高的乳酸菌,并对该菌株进行了菌落形态、生理生化及16S r DNA序列分析的鉴定实验,结果表明:该菌株为革兰氏阳性菌,菌落特征为白色,圆形,表面突起,不透明,边缘整齐,镜检发现该菌为球菌、直径为0.8μm,四联或成串排列,经生理生化及16S r DNA序列鉴定确定该菌为肠球菌属中的屎肠球菌(Enterococcus faecium),遗传稳定性较好。      

Interactions among lactic acid starter and probiotic bacteria used for fermented dairy products

Interactions among lactic acid starter and probiotic bacteria were investigated to establish adequate combinations of strains to manufacture probiotic dairy products. For this aim, a total of 48 strains of Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lactococcus lactis, Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium spp. (eight of each) were used. The detection of bacterial interactions was carried out using the well-diffusion agar assay, and the interactions found were further characterized by growth kinetics. A variety of interactions was demonstrated. Lb. delbrueckii subsp. bulgaricus was found to be able to inhibit S. thermophilus strains. Among probiotic cultures, Lb. acidophilus was the sole species that was inhibited by the others (Lb. casei and Bifidobacterium). In general, probiotic bacteria proved to be more inhibitory towards lactic acid bacteria than vice versa since the latter did not exert any effect on the growth of the former, with some exceptions. The study of interactions by growth kinetics allowed the setting of four different kinds of behaviors between species of lactic acid starter and probiotic bacteria (stimulation, delay, complete inhibition of growth, and no effects among them). The possible interactions among the strains selected to manufacture a probiotic fermented dairy product should be taken into account when choosing the best combination/s to optimize their performance in the process and their survival in the products during cold storage.     

传统发酵牦牛酸乳中高产胞外多糖乳酸菌的筛选与鉴定

目的:以四川红原、西藏羊八井地区传统牦牛酸乳中分离出的57株乳酸菌作为实验菌种,筛选出高产胞外多糖乳酸菌。方法:通过菌落拉丝法、硫酸-苯酚法的测定。结果:实验菌株胞外多糖产量在19.95⁹1.08μg/m L之间,其中菌株代号为32-2、67-1、41-1和27的胞外多糖产量较高,分别为91.08、89.76、87.22、87.40μg/m L。通过16S r DNA序列同源性鉴定表明代号32-2菌株鉴定为屎肠球菌（Enterococcus faecium）、代号67-1菌株为肠膜明串株菌肠膜亚种（Leuconostoc mesenteroides subsp.mesenteroides）、代号41-1菌株为干酪乳杆菌（Lactobacillus casei）、代号27菌株为肠膜明串珠菌（Leuconostoc mesenteroides）。结论:为研究具有提高酸乳品质能力的发酵菌株提供依据。      

定量PCR技术检测杀菌型产品中乳酸菌

目的利用定量PCR(quantitativePCR,qPCR)技术检测杀菌型产品中乳酸菌,并与标签标示相比较,查探产品中各类菌种的异同性及数量。方法以市售的发酵乳及含乳饮料作为研究对象,设计可区分产品中常见的6种乳酸菌特异性引物及探针,利用qPCR技术对方法的特异性、灵敏度进行验证,并建立标准扩增曲线;利用模拟样品对方法进行检验,最后对市场上购买的实际样品进行检测。结果除去干酪乳杆菌,其他5种引物都能特异性扩增出其目标菌,并且对其他的乳酸菌均无扩增现象;DNA检测的灵敏度可达到2～4pg;单一标准菌种扩增曲线线性较好,相关系数r2值在0.954～0.992之间;对模拟样品的检测,与平板法差异性比较,P值均大于0.05,无显著性差异。对市售样品进行检测,产品中标记的干酪乳杆菌、双歧杆菌和嗜热链球菌与检测结果存在不匹配现象。结论本研究建立的qPCR方法可快速、准确地对产品中德氏乳杆菌保加利亚亚种、嗜热链球菌、乳酸乳球菌、嗜酸乳杆菌、双歧杆菌的鉴定和定量的分析。     

Isolation and characterisation of lactic acid bacteria strains from raw camel milk for potential use in the production of fermented Tunisian dairy products

The aim of this work was to study the suitability of camel milk for the production of dairy products by lactic acid fermentation. Sixty strains of lactic acid bacteria (LAB) were isolated from camel milk. The strains were tested for their acidification activity, ability to use citrate, exopolysaccharide production, lipolytic, proteolytic activities and resistance to antibiotics. Ten strains were investigated for their ability to metabolize carbohydrates and that resulted in the identification of 5 Lactococcus lactis, 1 Lactobacillus pentosus, 2 Lactobacillus plantarum, 1 Lactobacillus brevis and 1 Pediococcus pentosaceus strains. Two strains of Lactococcus lactis SCC133 and SLch14 were selected to produce traditional Tunisian fermented dairy products (Lben, Raib, Jben cheese and Smen). These strains were chosen based on their acid production capacity and their ability to produce a high yield of biomass.     

Characterisation of lactic acid bacteria isolated from the Georgian,yoghurt‐like Matsoni

Matsoni is a traditional Caucasian fermented milk product, characterised by a lactic acid bacteria (LAB) microbiota. Objectives of the present study were to isolate and identify the LAB of Matsoni samples collected from various Georgian areas and to study their technological characteristics. About 300 LAB from 71 samples of Matsoni were isolated and characterised. The species most representatives were Lactobacillus delbrueckii, Streptococcus thermophilus and Lactobacillus rhamnosus. This study highlighted a high degree of biodiversity and a specific geographical distribution of the dominant LAB present in artisanal Matsoni. Some strains showed technological features useful to design a multistrain starter culture for Matsoni.     

Ester synthesis by lactic acid bacteria isolated from goat’s and ewe’s milk and cheeses

The present work evaluates the ability of lactic acid bacteria isolated from goat’s and ewe’s milk and cheeses to synthesise short-chain fatty acid esters. In order to elucidate the mechanisms of ester synthesis involved, cell-free extracts were incubated in sodium phosphate buffer containing triglyceride plus ethanol (alcoholysis) and free fatty acid plus ethanol (esterification). After 24 h incubation at 37 °C esters were extracted and determined by gas chromatography. Strains evaluated were able to synthesise ethyl esters from 2 to 10 carbon atoms, mainly ethyl butanoate and ethyl hexanoate. A great variability amongst strains was observed. In general, higher ester-forming activities by esterification were detected. In enterococci strains the alcoholysis mechanism was also involved.     

乳酸菌冷冻干燥保护剂的筛选

通过单因素比较和正交试验设计,确定适合保加利亚乳杆菌和嗜热链球菌的最佳冻干保护剂配方。通过对15种冻干保护剂单因素保护效果的比较,以及对选定的4种保护剂的正交试验结果,可以确定嗜热链球菌最佳冻干保护剂配方为脱脂乳粉12%、海藻糖1%、甘油3%、谷氨酸钠1%,保加利亚乳杆菌最佳冻干保护剂配方为脱脂乳粉8%、海藻糖1%、甘油2%、谷氨酸钠1.5%。     

Nitrite tolerance and nitrite reduction in lactic acid bacteria associated with cured meat products

The effect of 0, 50, 100 and 200 μg/ml of nitrite on the growth of isolated and reference strains of lactic acid bacteria associated with cured meat products was studied in broth cultures and the presence of an active nitrite reductase enzyme system in these strains was determined. Half of the 10 reference strains and 16 of 25 isolated strains were resistant to all levels of nitrite tested Strains which did not show a significant decrease in growth rate or cell yield in the presence of 200 μg/ml of nitrite under anaerobic conditions were homofermentative. All heterofermentative strains showed a decrease in growth rate or cell yield or both. Inhibition due to nitrite increased as the concentration increased and was greatest under anaerobic conditions. Enzymatic ability to reduce nitrite was detected in 5 homofermentative and 1 heterofermentative strains. The presence of an active nitrite reductase enzyme system in lactic acid bacteria was not related to their resistance to nitrite.     

Combined use of bacteriocin‐producing strains to control Listeria monocytogenes regrowth in raw pork meat

Avoiding the presence of Listeria in meat and dairy products is a major challenge for the food industry. In this work, a Lactobacillus curvatus strain producing the bacteriocin sakacin P and a Pediococcus acidilactici strain producing another bacteriocin, pediocin AcH, were used as starter cultures under laboratory conditions in a Listeria‐seeded raw‐pork‐meat matrix, which was then stored for 6 weeks at 4 °C. At 1 week intervals during the storage period, the antilisterial activity was evaluated. When either strain was added alone, the Listeria monocytogenes cfu count initially dropped from 10² cfu g^?1 to an undetectable level by the end of week 1 or 2, but this was followed by a rebound (regrowth) 1 week later. When both strains were added together to the meat matrix, rebound was delayed, Listeria remaining undetected from the end of week 1 to the end of week 5. A rebound was observed 6 weeks post‐inoculation, but fewer than 10 cfu g^?1 were counted. The use of more than one bacteriocin‐producing strain may thus overcome some of the problems limiting the effectiveness of bacteriocins in food systems.