Impact of a plant extract on the viability of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus in nonfat yogurt

The effect of a plant extract (prepared from olive, garlic, onion and citrus with sodium acetate as a carrier) on the viability of yogurt starter cultures was studied. Nonfat yogurt was prepared with various levels of supplements: plant extract (0, 0.5 or 1.0%, w/v) or l-cysteine HCl (0.014 or 0.028%, w/w). Microbial and physicochemical analyses were conducted weekly for 50 days. Fermentation time increased for supplemented yogurts compared with the non-supplemented yogurt. Lactobacillus bulgaricus counts in supplemented yogurts were >6 log cfu mL^?1 for a longer time (7–21 days) compared with the non-supplemented yogurt. Streptococcus thermophilus counts in all yogurts were > 6 log cfu mL^?1 throughout the storage. Overall, redox potential and titratable acidity of yogurts on day 50 were greater compared with day 1, but pH and syneresis were less. Plant extract at 0.5% enhanced L. bulgaricus viability in nonfat yogurt while least affecting the physicochemical characteristics.     

The critical role of urease in yogurt fermentation with various combinations of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus

The protocooperation between Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus relies on metabolite exchanges that accelerate acidification during yogurt fermentation. Conflicting results have been obtained in terms of the effect of the Strep. thermophilus urease and the NH₃ and CO₂ that it generates on the rate of acidification in yogurt fermentation. It is difficult to perform a systematic study of the effects of urease on protocooperation because it is necessary to distinguish among the direct, indirect, and strain-specific effects resulting from the combination of the strains of both species. To evaluate the direct effects of urease on protocooperation, we generated 3 urease-deficient mutants (ΔureC) of fast- and slow-acidifying Strep. thermophilus strains and observed the effects of NH₃ or CO₂ supplementation on acidification by the ΔureC strains. Further, we examined 5 combinations of 3 urease-deficient ΔureC strains with 2 CO₂-responsive or CO₂-unresponsive strains of L. bulgaricus. Urease deficiency induced a shortage of ammonia nitrogen and CO₂ for the fast- and slow-acidifying Strep. thermophilus and for the CO₂-responsive L. bulgaricus, respectively. Notably, the shortage of ammonia nitrogen had more severe effects than that of CO₂ on yogurt fermentation, even if coculture with L. bulgaricus masked the effect of urease deficiency. Our work established (1) that urease deficiency inhibits the fermentative acceleration of protocooperation regardless of the Strep. thermophilus and L. bulgaricus strain combinations, and (2) that urease is an essential factor for effective yogurt acidification.     

Growth, proteolytic, and ACE-I activities of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus and rheological properties of low-fat yogurt as influenced by the addition of Raftiline HP

This study investigated the influence of incorporating Raftiline HP on the pH, growth, proteolytic, and angiotensin-I converting enzyme inhibitory activities and on spontaneous whey separation, firmness, and rheological properties of low-fat yogurts during storage for 28 d at 4 degrees C. Three types of yogurts were prepared from skim milk containing 0% (YI0, control), 2% (YI2), and 3% (YI3) Raftiline HP, respectively. The incorporation of Raftiline HP improved the growth of starter organisms, particularly that of Lactobacillus delbrueckii ssp. bulgaricus, resulting in shorter fermentation time. There was a significant improvement in total proteolysis, which was highest in yogurt containing 3% Raftiline HP. The ACE inhibitory activity was maximal in YI3 compared to YI2 and YI0. Incorporation of Raftiline HP did not affect whey separation and firmness of the low-fat yogurts. All these products were more fluid like with distinct pseudoplastic properties and lesser ability to resist deformation upon applied shear.     

Exopolysaccharide production from whey lactose by fermentation with Lactobacillus delbrueckii ssp. bulgaricus

Ropy Lactobacillus delbrueckii ssp. bulgaricus (strain RR) was used for production of exopolysaccharide in sweet whey and simulated whey permeate (SWP) supplemented with combinations of lactose, KH₂PO₄, NH₄Cl, casamino acids, and mineral salts. Media were incubated at 32, 37, and 44°C for 72h. Periodic adjustment of pH to ～6.2 increased viscosity and lactose utilization, and the free galactose and lactic acid in the media. The effect of pH adjustment was greater than that of supplementation with nutrients or minerals. Fermentation of supplemented SWP generally produced lower viscosities than did fermentation of supplemented sweet whey. After 24h fermentation, viscosity decreased in pH adjusted media. Viscosity of media was highest when incubation was at 32°C and lowest with incubation at 44°C.     

Effect of lactose hydrolysis on the milk-fermenting properties of Lactobacillus delbrueckii ssp. bulgaricus 2038 and Streptococcus thermophilus 1131

Yogurt is a well-known nutritious and probiotic food and is traditionally fermented from milk using the symbiotic starter culture of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus. However, yogurt consumption may cause health problems in lactose-intolerant individuals, and the demand for lactose-free yogurt has been increasing. The standard method to prepare lactose-free yogurt is to hydrolyze milk by lactase; however, this process has been reported to influence the fermentation properties of starter strains. This study aimed to investigate the fermentation properties of an industrial starter culture of L. bulgaricus 2038 and S. thermophilus 1131 in lactose-hydrolyzed milk and to examine the metabolic changes induced by glucose utilization. We found that the cell number of L. bulgaricus 2038, exopolysaccharide concentration, and viscosity in the coculture of L. bulgaricus 2038 and S. thermophilus 1131 was significantly increased in lactose-hydrolyzed milk compared with that in unhydrolyzed milk. Although the cell number of S. thermophilus 1131 showed no difference, production of formic acid and reduction of dissolved oxygen were enhanced in lactose-hydrolyzed milk. Further, in lactose-hydrolyzed milk, S. thermophilus 1131 was found to have increased the expression of NADH oxidase, which is responsible for oxygen reduction. These results indicated that glucose utilization promoted S. thermophilus 1131 to rapidly reduce the dissolved oxygen amount and produce a high concentration of formic acid, presumably resulting in the increased cell number of L. bulgaricus 2038 in the coculture. Our study provides basic information on the metabolic changes in starter strains in lactose-hydrolyzed milk, and demonstrates that lactose-free yogurt with increased cell number of L. bulgaricus can be prepared without delay in fermentation and decrease in the cell number of S. thermophilus.     

Productions and monomer compositions of exopolysaccharides by Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus strains isolated from traditional home-made yoghurts and raw milk

In this study, a total of forty‐five strains of lactobacilli and streptococci were determined exopolysaccharide (EPS) production in skim milk and Man Rogosa and Sharpe (MRS)/M17 medium, viscosity and proteolytic activity. The exopolysaccharide production by lactobacilli strains during growth in MRS medium was twenty‐one to 211 mg L^?1, while in skim milk was to thirty‐six to 315 mg L^?1. The EPS production by streptococci strains during growth in M17 medium was sixteen to 114 mg L^?1, while in skim milk was to twenty‐four to 140 mg L^?1. The EPS production of strains was lower in MRS/M17 medium than skim milk. Results showed that it was not clear correlation between the viscosity and EPS production of some strains. All strains were shown proteolytic activity. Positive correlations between exopolysaccharide production and proteolytic activity in skim milk were found some strains of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. These results indicated that the high exocellular protease‐producing strains can produce high EPS in skim milk. The monomer compositions of the EPSs formed by selected five strains were analysed. Mannose dominated (99–100%) on the EPS produced by L. delbrueckii subsp. bulgaricus and S. thermophilusstrains (except L. delbrueckii subsp. bulgaricus 22) in skim milk and MRS/M17 medium. Besides, the EPSs of strains in skim milk contained small amount of lactose.     

酸乳中乳杆菌和链球菌的实时荧光定量分析

采用实时荧光定量分析了酸乳中的德氏乳杆菌L2和嗜热链球菌S1的数量,德氏乳杆菌L2的活菌数与细胞循环数的相互关系曲线为Y=-2.936logX+34.72(R2=0.998),采用平板计数法获得的样品中L2浓度为8.82×10smL-1,荧光定量的结果是8.78×108mL-1;嗜热链球菌S1活菌数与细胞循环教的相互关系曲线为Y=-3.03910gX+35.45(R2=0.995),采用平板计数法,获得的样品中嗜热链球菌S1浓度1.08×108mL-1,荧光定量的结果是1.06×108mL-1.实时荧光定量的方法适合于酸乳中乳酸菌的快速计数.     

嗜热链球菌和德氏乳杆菌保加利亚亚种共生关系的研究进展

嗜热链球菌和德氏乳杆菌保加利亚亚种是组成酸奶发酵剂的主要菌种,在长期共处于牛乳环境的过程中形成多种协同共生关系.这些协同共生关系赋予发酵剂菌株产酸快、黏度高、活性物质丰富等优良性能,同时对酸奶品质产生重要影响.该文旨在从营养供给、抵抗环境胁迫及酸奶品质改良等方面讨论两菌的协同共生关系,为提高发酵剂菌株活力及酸奶品质提供...     

保加利亚乳杆菌和嗜热链球菌相互作用的研究

探讨了嗜热链球菌和保加利亚乳杆菌之间的相互作用(拮抗和共生效果)，指出这两个菌种的许多菌株在代谢过程中会产生过氧化氢、细菌素等抑菌性物质，导致嗜热链球菌与保加利亚乳杆菌间表现出非协同生长的现象。在此基础上，建立了评价发酵剂之间相互作用的新的指标体系，旨在方便优良酸奶发酵剂菌种的筛选工作。     

Selective enumeration of Lactobacillus delbrueckii ssp. bulgaricus,Streptococcus thermophilus,Lactobacillus acidophilus,bifidobacteria, Lactobacillus casei,Lactobacillus rhamnosus,and propionibacteria

Nineteen bacteriological media were evaluated to assess their suitability to selectively enumerate Lactobacillus delbrueckii ssp. bulgaricus, Streptococcus thermophilus, Lactobacillus casei, Lactobacillus rhamnosus, Lactobacillus acidophilus, bifidobacteria, and propionibacteria. Bacteriological media evaluated included Streptococcus thermophilus agar, pH modified MRS agar, MRS-vancomycine agar, MRS-bile agar, MRS-NaCl agar, MRS-lithium chloride agar, MRS-NNLP (nalidixic acid, neomycin sulfate, lithium chloride and paramomycine sulfate) agar, reinforced clostridial agar, sugar-based (such as maltose, galactose, sorbitol, manitol, esculin) media, sodium lactate agar, arabinose agar, raffinose agar, xylose agar, and L. casei agar. Incubations were carried out under aerobic and anaerobic conditions at 27, 30, 37, 43, and 45 degrees C for 24, 72 h, and 7 to 9 d. S. thermophilus agar and aerobic incubation at 37 degrees C for 24 h were suitable for S. thermophilus. L. delbrueckii ssp. bulgaricus could be enumerated using MRS agar (pH 4.58 or pH 5.20) and under anaerobic incubation at 45 degrees C for 72 h. MRS-vancomycine agar and anaerobic incubation at 43 degrees C for 72 h were suitable to enumerate L. rhamnosus. MRS-vancomycine agar and anaerobic incubation at 37 degrees C for 72 h were selective for L. casei. To estimate the counts of L. casei by subtraction method, counts of L. rhamnosus on MRS-vancomycine agar at 43 degrees C for 72 h under anaerobic incubation could be subtracted from total counts of L. casei and L. rhamnosus enumerated on MRS-vancomycine agar at 37 degrees C for 72 h under anaerobic incubation. L. acidophilus could be enumerated using MRS-agar at 43 degrees C for 72 h or Basal agar-maltose agar at 43 degrees C for 72 h or BA-sorbitol agar at 37 degrees C for 72 h, under anaerobic incubation. Bifidobacteria could be enumerated on MRS-NNLP agar under anaerobic incubation at 37 degrees C for 72 h. Propionibacteria could be enumerated on sodium lactate agar under anaerobic incubation at 30 degrees C for 7 to 9 d. A subtraction method was most suitable for counting propionibacteria in the presence of other lactic acid bacteria from a product. For this method, counts of lactic bacteria at d 3 on sodium lactate agar under anaerobic incubation at 30 degrees C were subtracted from counts at d 7 of lactic bacteria and propionibacteria.     

Differentiation of Enterococcus faecium from Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus strains by PCR and dot-blot hybridisation

Variations in length and sequence of the 16S/23S spacer region of Enterococcus faecium provided the basis for development of simple PCR and dot-blot hybridisation assays that enabled the differentiation of potentially probiotic Enterococcus faecium strains from Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. Such assays may be useful for differentiation of yoghurt starter cultures and enterococcal strains when they are simultaneously present in probiotic food products.     

保加利亚乳杆菌与嗜热链球菌共生机理的研究进展

乳酸菌在乳中的共生机制是非常复杂的网络体系。通过对蛋白质代谢、核苷酸碱基代谢、氧化性应激以及碳源物质代谢等方面的研究,对保加利亚乳杆菌与嗜热链球菌共生机理的研究进展进行详细的阐述。旨在为发酵剂菌体的筛选及应用提供参考。     

不同发酵特性的嗜热链球菌与保加利亚乳杆菌共发酵的特性

为探究具有不同优良性状的嗜热链球菌株与保加利亚乳杆菌株共发酵的特性,用产酸快的嗜热链球菌StCH-1菌株和产黏好的嗜热链球菌StTA040菌株与保加利亚乳杆菌Lb0925B菌株组合,测定其组合菌株的发酵性能。通过实验发现组合菌株发酵速率均比单菌株发酵速率快,其中含有嗜热链球菌StCH-1的组合菌株发酵速率较快,而含有嗜热链球菌StTA040的组合菌株的胞外多糖产量较高,发酵乳的黏度较高,持水力较强;三组分发酵剂的发酵速率快,发酵乳在贮藏期间黏度高,持水力强,通过感官分析得出三组分发酵剂制得的发酵乳的口感和风味最佳。     

The differential enumeration of Lactobacillus delbrueckii subspecies bulgaricus and Streptococcus salivarius subspecies thermophilus in yogurt and labneh using an improved whey medium

Bromocresol green whey agar (BGWA), an elective differential medium for yogurt bacteria, was prepared by mixing 2 parts of whey obtained by autoclaving (121°C/15 min) reconstituted non-fat dry milk (NFDM) (15% w/w; pH 5.7 by 1 N HCl) with 1 part of a sterile agar solution (115°C/15 min) containing 3% yeast extract, 1.2% K₂HPO₄, 0.004% bromocresol green and 4% agar. Lactobacillus delbrueckii subsp bulgaricus colonies in BGWA pour plates were light in colour and in the form of an irregular mass with twisted filament projections, while Streptococcus salivarius subsp thermophilus colonies were green lenticular with entire edges. BGWA performed generally better than deMan-Rogosa-Sharpe agar and M17 agar when L bulgaricus and S thermophilus respectively were enumerated in samples of commercial yogurt and labneh (yogurt concentrated by removing part of its whey) and in single cultures of yogurt bacteria in NFDM. Immediately after processing, the counts of yogurt bacteria in labneh samples were similar to those of yogurt samples, indicating a loss of these bacteria with whey during processing. The decrease in the numbers of yogurt bacteria in labneh samples at the end of the shelf-life (14 days at 7°C) was slight, indicating a relative resistance of these bacteria to acidity and refrigeration.     

Rheological and physical characteristics of non-fat set yogurt prepared with EPS-producing Streptococcus thermophilus and an H+-ATPase-defective mutant Lactobacillus delbrueckii subsp. bulgaricus

The rheological and physical characteristics of non-fat set yogurt produced using co-cultures of ropy EPS-producing Streptococcus thermophilus S3.3 and Lactobacillus delbrueckii subsp. bulgaricus LTM and of Streptococcus thermophilus S3.3 and Lactobacillus delbrueckii subsp. bulgaricus H+-ATPase-defective mutant L6 under different conditions were studied. Yogurts produced with mutant L6 had a higher pH and water-holding capacity and better textural properties compared to those produced with the LTM strain. The highest storage modulus (G′) and thixotropic loops were found for yogurt made with L6 at 42°C on day 21 of cold storage. This yogurt contained a network of thick, continuous protein aggregates and large void spaces.     

Effects of glutathione on acid stress resistance and symbiosis between Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus

Streptococcus thermophilus SDMCC18 contains a novel bi-functional glutathione synthetase gene gshF, and it can produce glutathione (GSH). In the present study, we demonstrated that the produced GSH by S. thermophilus SDMCC18 could protect cells against acid challenge and be secreted into the medium. Moreover, using a gshF-defective mutant strain as the control, we found that the GSH conferred a protective role against acid stress to Lactobacillus delbrueckii subsp. bulgaricus ATCC11842. In addition, L. bulgaricus ATCC11842 could import the exogenous GSH into the cytoplasm, leading to an improved growth of strain ATCC11842. Taken together, our study reported a novel proto-cooperation relationship between S. thermophilus and L. bulgaricus in yoghurt fermentation.     

保加利亚乳杆菌和嗜热链球菌生物膜形成研究

采用置片法和菌落计数法对嗜热链球菌(Streptococcus thermophilus)和保加利亚乳杆菌(Lactobacillus bulgaricus)在不同载体表面(椰果粒、不锈钢网布、塑料片、陶瓷片和玻璃片)上形成生物膜的能力进行研究。结果表明：椰果粒和不锈钢网布是适宜乳酸菌单菌生物膜形成的载体,培养7d椰果粒和不锈钢网布上的单菌生物膜初始菌密度可达107CFU/cm2,并且在后续培养中能稳定在3.2×106CFU/cm2左右;混菌生物膜菌密度连续7d稳定在1×107CFU/cm2左右。利用扫描电镜对S. thermophilus和L. bulgaricus形成的混菌生物膜进行观察,结果表明在椰果粒和不锈钢网布表面上S. thermophilus和L. bulgaricus形成典型的混菌生物膜结构。     

摄入酸奶对辐照小鼠体重和免疫细胞的影响

辐射前后5d用含保加利亚乳杆菌和嗜热链球菌活菌的酸奶添加于饲料中饲喂小鼠，比较接受2Gy辐射小鼠的体重、胸腺细胞重量、腹膜巨噬细胞吞噬活性和脾淋巴细胞计数等指标，发现摄入添加酸奶饲料的处理小鼠与普通饲料对照组有显著的差异，证明饲喂酸奶对辐射后小鼠产生了保护作用，减轻其体重下降、胸腺重下降和淋巴细胞计数，提高其巨噬细胞吞噬活性。