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。     

发酵奶中乳酸菌菌种检出及活菌计数调查

目的分析北京市场发酵奶(酸奶)在保质期内的乳酸菌数及乳酸菌菌种的检出率。方法对11个酸奶厂家的20种不同酸奶产品进行乳酸菌活菌计数及所用菌种的检验。结果在保质期间,双歧杆菌和嗜酸乳杆菌检出率分别为23.08%和27.27%;保加利亚乳杆菌与嗜热链球菌分别为72.22%和94.44%。在保质期末,嗜热链球菌的平均活菌数为3.23×106CFU/ml,保加利亚乳杆菌为4.17×105CFU/ml,双歧杆菌为1.12×104CFU/ml,嗜酸乳杆菌为1.32×104CFU/ml。结论酸奶中嗜热链球菌和保加利亚乳杆菌的检出率及活菌数均高于双歧杆菌和嗜酸乳杆菌。     

羊奶酸奶优良发酵菌株的筛选

以保加利亚乳杆菌和嗜热链球菌为发酵菌种,选育适合羊奶酸奶发酵的优良菌株。通过对4株保加利亚乳杆菌和4株嗜热链球菌在羊乳中发酵特性进行研究。结果表明,4株保加利亚乳杆菌中,L.b-800菌株产酸速度较快,后酸化能力较弱,且乳酸菌活菌数较高;4株嗜热链球菌中,S.t-499菌株产酸速度较快,产粘能力较强,且乳酸菌活菌数较高。优良菌株L.b-800和S.t-499配比为2:1～1:2时,羊奶酸奶发酵酸度适中,粘度适宜,无乳清析出,乳酸菌活菌数高达1×109cfu/mL以上。     

分段发酵提高酸乳中活菌总数的研究

为提高酸乳中乳酸菌活菌数量,在测定不同温度下嗜酸乳杆菌生长曲线及保加利亚乳杆菌与嗜热链球菌1∶1混菌发酵生长曲线的基础上,采用分段发酵的方式,发酵初期按1%接种量接入嗜酸乳杆菌,待发酵进行4h,嗜酸乳杆菌的数量达到107时,再接入保加利亚乳杆菌和嗜热链球菌,接种量均为1%。发酵结束后,测得最终活菌数可达109,相比3种菌一次性接种发酵,活菌数量提高了1个数量级。     

不同酸奶微生物的实时荧光定量PCR比较研究

采用实时荧光定量PCR技术对不同酸奶中乳酸菌、嗜热链球菌、保加利亚乳杆菌和大肠菌群等主要微生物进行了比较研究。结果表明,不同酸奶中乳酸菌总数和大肠菌群均显著高于国家标准。不同酸奶中乳酸菌总数差异显著,1号酸奶比2号高63%,而3号又是1号的2.45倍。1号酸奶的嗜热链球菌和保加利亚乳杆菌明显高于2号或3号,而2号和3号却差异不明显。     

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。     

罗地亚9001直投型发酵剂发酵特性研究

利用罗地亚90001直投型发酵剂来发酵酸奶，探讨了利用直投型发酵剂发酵的酸奶不能作为后续发酵剂进行酸奶生产的原因。在实验中首先利用直投型发酵剂发酵牛乳，然后依次利用各代次产物作为后续发酵剂生产酸奶，直至第6代牛乳不能再正常发酵为止。同时，对每代酸奶中嗜热链球菌和保加利亚乳杆菌进行计数，并观察嗜热链球菌和保加利亚乳杆菌比例上的变化。最后将第6代不能正常发酵酸奶中的嗜热链球菌和保加利亚乳杆菌分离并进行鉴定。将二者按1：1(数量比)的比例接种牛乳，发现牛乳能够正常发酵。结果表明。利用酸奶作为后续发酵剂的第6代牛乳不能正常发酵的原因是嗜热链球菌和保加利亚乳杆菌的数量比发生变化。而导致此情况发生的原因可能是由于低温下二者的生长速率不同。     

提高嗜酸乳杆菌酸乳菌活力的研究

以嗜酸乳杆菌为主发酵剂,嗜热链球菌和保加利亚乳杆菌为辅助发酵剂制作嗜酸乳杆菌酸乳,采用正交实验,并分析发酵过程中pH、乳酸菌数以及感官品质的变化,确定混合菌种的最佳比例。结果表明,嗜酸乳杆菌1.8%、嗜热链球菌1.4%、保加利亚乳杆菌0.6%混合发酵,可以提高乳中嗜酸乳杆菌的菌活力并改善其风味。经验证,混合菌种发酵制作的酸奶在风味和保健功能等方面明显优于单一菌种发酵制作的酸乳。     

酸奶发酵菌生长代谢的动力学特性

本文研究了酸奶凝固过程中嗜热链球菌及保加利亚乳杆菌两种混合发酵菌的生长代谢动力学。结果表明，嗜热链球菌、保加利亚乳杆菌及其乳酸菌总数在牛奶基质中的平均世代时间分别为８７＇４８″、７８＇３３″、８４＇０５″，本研究还试图建立了本菌生长代谢动力学的５个线性数学模型。     

益生菌酸奶的工艺研究

以保加利亚乳杆菌(Lb)、嗜热链球菌(St)、干酪乳杆菌(Lc)、罗依氏乳杆菌(Lr)混合菌发酵,得到益生菌酸奶.正交结果表明,干酪乳杆菌、罗依氏乳杆菌可以应用于酸奶发酵,发酵工艺为:保加利亚乳杆菌:嗜热链球菌:干酪乳杆菌:罗依氏乳杆菌为3:3:2:2,发酵温度39℃,接种量0.25%(DVS),加糖量8%,凝乳时间5h.     

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.     

Improved media for differentiation of rods and cocci in yogurt

Selected yogurt starters and commercial samples grew on Elliker's lactic agar supplemented with .1% Tween 80 and 50 micrograms/ml of 2,3,5-triphenyltetrazolium chloride to produce small, red Streptococcus thermophilus colonies and larger, white Lactobacillus bulgaricus colonies. The distinction was somewhat strain dependent but was satisfactory in most cases. Addition of 7% skim milk (11% solids) to lactic agar in place of 2,3,5-triphenyltetrazolium chloride allowed good rod-coccus differentiation, regardless of strain or yogurt brand. On this medium, called yogurt lactic agar, L. bulgaricus appeared as large white colonies surrounded by a cloudy zone and S. thermophilus as smaller white colonies devoid of a surrounding halo. Casein precipitation was responsible for the halo effect around the more acidogenic L. bulgaricus colonies. Yogurt lactic agar compared favorably with S. thermophilus and Lactobacillus agar media for the recovery of S. thermophilus and L. bulgaricus in single and mixed cultures.     

地木耳酸奶的研制

在灭菌牛乳中添加地木耳不同浓度水提物,接种保加利亚乳杆菌和嗜热乳链球菌进行发酵,结合理化分析、感官评分、微生物检测等方法,得到地木耳提取物浓度与乳酸菌活菌数和酸奶风味之间的关系。结果表明,地木耳水提物对乳酸菌的生长繁殖有很大的促进作用,能缩短酸奶的后熟时间,而且能够产生特殊的香味物质,同时对酸奶的感官颜色没有产生不良影响。在鲜奶中加入地木耳水提物10%,加入接种量为10%的乳酸菌,40℃发酵5h,后熟12h后研制得到地木耳酸奶,成品质量指标符合国标。     

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.     

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.     

Evaluation of the possible use of potentially probiotic Lactobacillus strains in dairy products

In the study, the ability of two potentially probiotic strains Lactobacillus plantarum 14 and Lactobacillus fermentum 4a to milk fermentation and the possibility to use them in yogurt production were investigated. The strains did not acidify milk during 24 h and 72 h fermentation at 37C, but grew well and remained at the level of 10⁸ colony-forming units (CFU)/mL during 21 days of cold storage. Their application to yogurt production along with commercial starter culture consisted on L. delbrueckii ssp. bulgaricus and S. thermophilus allowed to obtain products with typical sensory properties, pH values and numbers of potentially probiotic bacteria at desired level 10⁷ CFU/mL.     

柠檬红茶酸奶的加工工艺研究

以柠檬、红茶和鲜奶为主要原料,以嗜热性链球菌和保加利亚乳杆菌为发酵剂,经发酵制成一种新型固体酸奶。通过正交试验方法和感官评定,确定该产品的最佳配方和生产工艺为：柠檬红茶汁5%,蔗糖和蜂蜜4%,保加利亚乳杆菌和嗜热性链球菌3％,发酵温度42℃、发酵时间5h。     

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.     

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.