不同乳酸菌对凝固型荔枝酸奶的发酵特性和质构的影响

以纯牛奶和荔枝汁为主要原料,以干酪乳杆菌、保加利亚乳杆菌和嗜热链球菌为发酵菌种,探讨三种乳酸菌的不同组合发酵对凝固型荔枝酸奶的发酵特性和质构的影响。结果表明:干酪乳杆菌产胞外多糖能力较强,单独发酵时胞外多糖含量达到22.50g/L,而嗜热链球菌和保加利亚乳杆菌单独发酵时胞外多糖的含量分别为5.73 g/L和0.29 g/L;各种不同乳酸菌组合发酵后酸奶的表观粘度和持水力与胞外多糖的含量呈正相关(R2=0.98);干酪乳杆菌产酸能力弱,单独发酵后p H高于其它添加有嗜热链球菌和保加利亚乳杆菌的组合,导致酸奶的硬度偏低,但干酪乳杆菌联合嗜热链球菌或保加利亚乳杆菌发酵时,发酵酸奶的硬度和乳酸菌活菌数均明显优于单独发酵组。因此,当干酪乳杆菌与嗜热链球菌及保加利亚乳杆菌联合发酵时,能充分发挥三个菌种的各自优势,菌落总数、胞外多糖含量和质构均能达到较好的品质水平。     

红曲酸奶中乳酸菌变化情况研究

利用超声波浸提法提取红曲中的有效成分,将红曲水提取液与全脂奶粉混合发酵制成新型红曲酸奶。通过荧光原位杂交（FISH）技术跟踪发酵过程中乳酸菌含量的变化,结果表明：红曲酸奶中保加利亚乳杆菌和嗜热链球菌数量显著高于普通酸奶。发酵2 h时,红曲酸奶中保加利亚乳杆菌与嗜热链球菌菌体数量分别为普通酸奶的2.63和2.24倍;发酵5 h时,发酵接近终点,红曲酸奶中保加利亚乳杆菌与嗜热链球菌菌体数量分别为普通酸奶的2.29和2.75倍。红曲酸奶的保藏期可达15 d,乳酸菌数符合国家标准的要求。     

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.     

Effect of thermophilic lactic acid bacteria on the viability of Salmonella serovar Typhimurium PT8 during milk fermentation and preparation of buffalo's yogurt

Viability of dairy-borne Salmonella enterica ssp. enterica serovar Typhimurium PT8 was studied during the fermentation of skim milk by thermophilic lactic acid bacteria (LAB). Longer generation times of Salmonella were found in mixed cultures of skim milk containing Streptococcus thermophilus, Lactobacillus delbrueckii ssp. bulgaricus or a mixture of them (1:1), as compared with single cultures of the pathogen. Salmonella was less able to survive in mixed cultures with these LAB during prolonged incubation at 41°C and also during cold storage of the fermented milk. L actobacillus ssp. bulgaricus and its mixture with S. thermophilus were more inhibitory to the growth and survival of Salmonella than was S. thermophilus . This was associated with higher ability of L . ssp. bulgaricus and the mixture to develop acidity in milk than S. thermophilus . Examining the antibacterial activity of these LAB towards Salmonella showed that other factors including heat-resistant and heat-labile compounds were involved in inhibiting the pathogen by these cultures. The viability of the same Salmonella strain during the preparation and cold storage of buffalo's yogurt was also examined. Salmonella was found to survive longer in yogurt made with starter containing probiotic bacteria than in that prepared with the traditional starter. This was ascribed to the development of lower pH by the traditional starter.     

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.     

Effects of fructooligosaccharide and whey protein concentrate on the viability of starter culture in reduced-fat probiotic yogurt during storage

ABSTRACT:  Viability of yogurt starter cultures and Bifidobacterium animalis was assessed during 28 d storage in reduced-fat yogurts containing 1.5% milk fat supplemented with 1.5% fructooligosaccharide or whey protein concentrate. These properties were examined in comparison with control yogurts containing 1.5% and 3% milk fat and no supplement. Although fructooligosaccharide improved the viability of Streptococcus thermophilus , Lactobacillus delbrueckii subs. bulgaricus, and Bifidobacterium animalis , the highest growth was obtained when milk was supplemented with whey protein concentrate in reduced-fat yogurt ( P < 0.05). Supplementation with 1.5% whey protein concentrate in reduced-fat yogurt increased the viable counts of S. thermophilus , L. delbrueckii subs. bulgaricus, and B. animalis by 1 log cycle in the 1st week of storage when compared to control sample. Similar improvement in the growth of both yogurt bacteria and B. animalis was also obtained in the full-fat yogurt containing 3% milk fat and no supplement. Addition of whey protein concentrate also resulted in the highest content of lactic and acetic acids ( P < 0.05). A gradual increase was obtained in organic acid contents during the storage.     

嗜热链球菌噬菌体对酸奶质量的影响

研究嗜热链球菌噬菌体对酸奶直投式发酵剂(direct vat set,DVS)发酵产酸、嗜热链球菌与保加利亚乳杆菌比例、酸奶黏度、口感、后酸化、乳清析出等方面的影响。结果表明：嗜热链球菌噬菌体可影响酸奶发酵剂发酵产酸、明显改变酸奶嗜热链球菌与保加利亚乳杆菌比例,导致产品黏度降低、口感变差、乳清析出及后酸化严重,嗜热链球菌噬菌体对DVS 生产酸奶有着严重的危害。     

Proteolytic profiles and angiotensin-I converting enzyme and alpha-glucosidase inhibitory activities of selected lactic acid bacteria

ABSTRACT:  This study was conducted to examine the growth, proteolytic profiles as well as angiotensin-I converting enzyme (ACE) and α-glucosidase (α-glu) inhibitory potentials of selected strains of lactic acid bacteria (LAB). Two strains each of yogurt bacteria ( Streptococcus thermophilus —1275 and 285, and Lactobacillus delbrueckii ssp. bulgaricus —1092 and 1368), and probiotics ( L. acidophilus —4461 and 33200, and L. casei —2607 and 15286, and 1 strain of Bifidobacterium longum 5022), were cultivated in reconstituted skim milk (RSM) at 37 °C and their proteolytic profiles and ACE as well as α-glu inhibitory activities were determined. Among all the strains of lactic acid bacteria studied, yogurt bacteria grew very well, with the exception of L. delbrueckii ssp. bulgaricus 1368 which showed a slower growth during the initial 3 h of incubation. The growth pattern corresponded well with the decrease in pH for the organisms. All the organisms showed an increase in proteolysis with time. The variations in proteolytic capabilities translated into corresponding variations in ACE inhibitory potential of these organisms. Bifidobacterium longum 5022 showed the highest ACE inhibitory potential followed by L. delbrueckii ssp. bulgaricus 1368, L. casei 15286, S. thermophilus 1275, and L. acidophilus 4461. Organisms with high intracellular enzymatic activities grew well. Also, aminopeptidases of strains of L. acidophilus 4461 and S. thermophilus 1275 that could better utilize proline containing substrates showed enhanced ACE inhibitory potential. Lactic acid bacteria possessed the ability to inhibit α-glu activity, which endowed them an antidiabetic property as well.     

Contribution of Streptococcus thermophilus to growth-stimulating effect of yogurt on rats

The origin of the growth-stimulating factor in yogurt was studied in rats fed liquid or freeze-dried diets of milk, yogurt, milks fermented individually by Streptococcus thermophilus and Lactobacillus bulgaricus, milks to which cells of Streptococcus thermophilus and Lactobacillus bulgaricus were added. Diets containing sonicated cells, cell supernatant, and cell fractions also were fed. Milk fermented by Streptococcus thermophilus and milk plus Streptococcus thermophilus cells stimulated growth as effectively as did yogurt. That finding and the absence of stimulation in rats fed Lactobacillus bulgaricus showed that Streptococcus thermophilus is responsible for stimulation of growth by yogurt. Growth was stimulated by an intracellular factor and not by fermentative changes in the milk.     

Influence of temperature on associative growth of Streptococcus thermophilus and Lactobacillus bulgaricus

Compatibility of Streptococcus thermophilus and Lactobacillus bulgaricus during associative growth as dependent on optimum growth temperature was determined. Optimum growth temperatures for 9 strains of S. thermophilus and 10 strains of L. bulgaricus ranged from 35 to 42 degrees C for S. thermophilus and 43 to 46 degrees C for L. bulgaricus. Streptococcus thermophilus and L. bulgaricus strains exhibiting similar to divergent optimum growth temperatures were combined (1:1 vol/vol) and incubated in milk at 37, 42, and 45 degrees C until pH 4.2 was reached. Initial and postincubation cell numbers were determined by plate count method. Streptococcus thermophilus strains reached greater cell numbers than L. bulgaricus at 37, 42, and 45 degrees C in 93.3% of the mixed culture trials. Average rod-coccus ratios obtained at 37, 42, and 45 degrees C were 1:2.2, 1:8, and 1:2.4, respectively. Optimum growth temperatures had no influence on growth of L. bulgaricus and S. thermophilus in mixed culture. Rather, temperature appeared to influence compatibility by determining the concentration or type of stimulatory factor(s) produced by L. bulgaricus. All strains of S. thermophilus exhibited an uncoupling of growth from acid production. Optimum temperature for acid production ranged from 2 to 8 degrees C above optimum growth temperature. These findings warrant consideration in the manufacture of yogurt and other fermented milk products.     

发酵羊奶中乳酸菌耐热菌株的筛选

对从商业乳酸菌发酵剂分离纯化的11株保加利亚乳杆菌和11株嗜热链球菌在发酵羊奶中的耐热性进行了研究。结果表明,保加利亚乳杆菌L.b-346和L.b-124菌株、嗜热链球菌S.t-883菌株和S.t-124菌株的耐热性较好;当L.b-346菌株、L.b-124菌株与S.t-883菌株、S.t-124菌株按杆菌和球菌以不同比例配合时,L.b-346菌株与S.t-124菌株以1∶2比例配合,可获得较高的耐热性。     

高粘稠性搅拌型刺梨酸奶的研制

以新鲜优质牛奶为原料,添加刺梨果浆.将保加利亚乳杆菌及嗜热链球菌以1:2混合作为发酵剂发酵,研制出具有刺梨风味的高粘稠性搅拌型酸奶。     

Short communication: effect of oxygen on symbiosis between Lactobacillus bulgaricus and Streptococcus thermophilus

Lactobacillus delbrueckii ssp. bulgaricus (L. bulgaricus) and Streptococcus thermophilus are traditionally used for the manufacture of yogurt. It is said that a symbiotic relationship exists between Strep. thermophilus and L. bulgaricus and this decreases fermentation time. It is well known that L. bulgaricus is stimulated by the formate produced by Strep. thermophilus, and Strep. thermophilus is stimulated by free amino acids and peptides liberated from milk proteins by L. bulgaricus in symbiotic fermentation. We found that acid production by starter culture LB81 composed of L. bulgaricus 2038 and Strep. thermophilus 1131 was greatly accelerated by decreasing dissolved oxygen (DO) to almost 0 mg/kg in the yogurt mix (reduced dissolved oxygen fermentation) and that DO interferes with the symbiotic relationship between L. bulgaricus 2038 and Strep. thermophilus 1131. We attributed the acceleration of acid production of LB81 by reduced dissolved oxygen fermentation mainly to the acceleration of formate production and the suppression of acid production of LB81 by DO mainly to the suppression of formate production.     

发酵羊乳中乳酸菌低产粘菌株的筛选

对从商业乳酸菌发酵剂分离纯化的11株保加利亚乳杆菌和11株嗜热链球菌在发酵羊乳中的粘度进行了研究。结果表明,保加利亚乳杆菌L.b-124菌株和L.b-346菌株、嗜热链球菌S.t-222菌株和S.t-346菌株具有较低的产粘能力,凝乳时间也较短;将L.b-346菌株与S.t-346菌株按杆菌和球菌1:1比例混合后在43℃下发酵羊乳时,可获得较低的发酵粘度。     

Use of chemical mutagenesis for the isolation of food grade beta-galactosidase overproducing mutants of bifidobacteria, lactobacilli and Streptococcus thermophilus

A classical chemical mutagenesis protocol was evaluated for increasing beta-galactosidase production by probiotic bacteria to improve their potential to treat symptoms of lactose malabsorption in humans. Two Bifidobacterium species (B. breve and B. longum) and one strain each of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus were tested by a single exposure to two chemical mutagens, ethyl methanesulfonate (EMS) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). To screen for beta-galactosidase (beta-gal) overproducing mutants, optimized EMS and MNNG mutant pots for each strain were plated on BHI agar containing 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-gal). Colonies that exhibited a blue color were selected for quantitative beta-gal activities using the o-nitrophenyl-beta-galactoside (ONPG) assay. Seventy-five mutants were obtained out of more than 2 million colonies screened and showed increased beta-galactosidase activities compared with the wild-type strains. EMS gave a higher frequency of beta-gal overproducing mutants than MNNG for three of the four strains, S. thermophilus, B. breve, and B. longum, whereas the frequency of L. delbrueckii ssp. bulgaricus beta-gal mutants was similar with both mutagens. The highest beta-gal increases, when induced during growth in lactose, for mutants of each culture were 137% for L. delbrueckii ssp. bulgaricus; 104% for S. thermophilus; 70% for B. breve; and 222% for B. longum mutants. This food-grade classical approach has the ability to moderately increase beta-gal concentrations in probiotic cultures to improve their potential for treating the symptoms of lactose malabsorption in humans.     

Commercially important characteristics of Turkish origin domestic strains of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus

Thirty native (Turkish origin) strains of Streptococcus thermophilus and 24 strains of Lactobacillus delbrueckii ssp. bulgaricus were isolated and identified. These strains were examined for their technologically important properties such as acidification, proteolysis, acetaldehyde production and antimicrobial activity. By taking into consideration their phage resistant properties, two strains of S. thermophilus (St.7.7, and St.26.2) and one of L. bulgaricus, numbered as 2004, were found to have the potential to be starters for yogurt production.     

凝固型鹰嘴豆酸乳的发酵工艺研究

以鹰嘴豆和复原乳为主要原料,通过保加利亚乳杆菌和嗜热链球菌发酵得到鹰嘴豆酸奶。结果表明:膨胀鹰嘴豆以6倍质量的水进行磨浆,再与复原乳以1∶1混合,通过保加利亚乳杆菌和嗜热链球菌1∶1混合发酵,接种量6%,加糖量5%,发酵温度42℃,发酵时间6～7 h。     

Effects of ingestion of yogurts containing Bifidobacterium and Lactobacillus acidophilus on spleen and Peyer's patch lymphocyte populations in the mouse

Certain probiotic lactic acid bacteria have been reported to improve immune system function. Here, the effects of ingesting yogurts on lymphocyte populations in the spleens and Peyer's patches were determined in mice. Three probiotic-supplemented yogurts containing Streptococcus thermophilus, Lactobacillus bulgaricus, Bifidobacterium, and Lactobacillus acidophilus and one conventional yogurt containing only S. thermophilus and L. bulgaricus were prepared from commercial starter cultures and used in the study. B6C3F1 female mice were fed the four different types of yogurts mixed with an AIN-93G diet in a 50:50 (wt/wt) ratio. Nonfat dry milk mixed at a 50:50 (wt/wt) ratio with AIN-93G diet was used as the control. After a 14-day feeding period, spleen and Peyer's patches were removed and lymphocytes subjected to phenotype analysis by flow cytometry. Ingestion of the four yogurts had no effect on percentages of CD8+ (cytotoxic T cells), B220+ (B cells), IgA+, or IgM+ cells in spleen or Peyer's patches. The percentage of CD4+ (T helper) cells was significantly increased in the spleens from one group of mice fed a yogurt containing Bifidobacterium and L. acidophilus, and a similar trend was found in the remaining two probiotic-supplemented yogurts. Effects on CD4+ populations were not observed in spleens of mice fed conventional yogurt or in the Peyer's patches of any of the four yogurt groups. In total, the results suggested that ingestion of conventional or probiotic-supplemented yogurts for 2 weeks had very little effect on lymphocyte distribution in the systemic or mucosal immune compartments.     

Effect of addition of Versagel on microbial, chemical, and physical properties of low-fat yogurt

The objective of this study was to examine the effect of Versagel on the growth and proteolytic activity of Streptococcus thermophilus 1275 and Lactobacillus delbrueckii ssp. bulgaricus 1368 and angiotensin-I converting enzyme inhibitory activity of the peptides generated thereby as well as on the physical properties of low-fat yogurt during a storage period of 28 d at 4 degrees C. Three different types of low-fat yogurts, YV0, YV1, and YV2, were prepared using Versagel as a fat replacer. The fermentation time of the low-fat yogurts containing Versagel was less than that of the control yogurt (YV0). The starter cultures maintained their viability (8.68 to 8.81 log CFU/g of S. thermophilus and 8.51 to 8.81 log CFU/g of L. delbrueckii ssp. bulgaricus) in all the yogurts throughout the storage period. There was some decrease in the pH of the yogurts during storage and an increase in the concentration of lactic acid. However, the proteolytic and ACE-inhibitory potential of the starter cultures was suppressed in the presence of Versagel. On the other hand, the addition of Versagel had a positive impact on the physical properties of the low-fat yogurt, namely, spontaneous whey separation, firmness, and pseudoplastic properties.     

Characterisation of lactic acid bacteria isolated from fermented milk "laban"

The technological properties of 96 lactic acid bacteria isolated from Lebanese traditional fermented milk "laban" were characterised. They were classified by phenotypic and biochemical analyses as Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, thus indicating that laban is a fermented milk similar to yogurt. Most strains of L. bulgaricus (87.5%) exhibited a high acidification activity, whereas strains of streptococci showed low acidification ability. 33.3% of streptococci strains and 25% of lactobacilli strains displayed similar acidification performances as European strains. Results obtained for syneresis, texture and rheological parameters led us to consider that isolated strains were not low polymer-producing strains. Some of them displayed interesting characteristics such as low syneresis and high values for rheological parameters. The major flavour compounds found in pure cultures were acetaldehyde, acetone, 2-butanone, dimethyl disulfide, acetoin, 2,3-butanedione, 2,3-pentanedione, and acetic, hexanoic and butanoic acids. Acetaldehyde (7.4%) and organic acids (48.3%) were mainly produced by L. bulgaricus strains, whereas streptococci cultures contained high relative levels of 2,3-butanedione and acetoin, which represented around 82% of the total flavour compounds. Finally, strains isolated from laban samples exhibited different technological properties than those used in yogurt production, thus conferring specific characteristics to this product.