H+‐ATPase‐Defective Variants of Lactobacillus delbrueckii subsp. bulgaricus Contribute to Inhibition of Postacidification of Yogurt during Chilled Storage

Continued acid production by Lactobacillus delbrueckii subsp. bulgaricus during the chilled storage of yogurt is the major cause of postacidification, resulting in a short shelf life. Two H⁺‐ATPase defective variants of L. delbrueckii subsp. bulgaricus were successfully isolated and their H⁺‐ATPase activities were reduced by 51.3% and 34.3%, respectively. It was shown that growth and acid production of variants were remarkably inhibited. The variants were more sensitive to acidic condition and had a significant rate for inactivation of H⁺‐ATPase by N, N‐dicyclohexylcarbodiimide (DCCD), along with a low H⁺‐extrusion, suggesting that H⁺‐ATPase is direct response for H⁺‐extrusion. In addition, the variants were also more sensitive to NaCl, while H⁺‐ATPase activities of variants and parent strain were significantly enhanced by NaCl stress. Obviously, H⁺‐ATPase might be involved in Na⁺ transportation. Furthermore, variants were inoculated in fermented milk to ferment yogurt. There was no significant difference in flavor, whereas the postacidification of yogurt during chilled storage was remarkably inhibited. It is suggested that application of L. delbrueckii subsp. bulgaricus with reduced H⁺‐ATPase activity in yogurt fermentation is one of effect, economic and simple avenues of inhibiting postacidification of yogurt during refrigerated storage, giving a longer shelf life. Practical Application: During yogurt fermentation, continued acid production by Lactobacillus delbrueckii subsp. bulgaricus during the chilled storage of yogurt leads to milk fermentation with high postacidification, resulting in a short shelf life. In this work, 2 acid‐sensitive variant strains of L. delbrueckii subsp. bulgaricus were isolated. The characteristics related to H⁺‐ATPase were compared and it was observed that milk fermented by the variants had lower postacidification, giving a longer shelf life. Application of L. delbrueckii subsp. bulgaricus with reduced H⁺‐ATPase activity in yogurt fermentation might be one of effect, economic and simple avenues of inhibiting yogurt postacidification during chilled storage, giving a longer shelf life.     

红参对乳酸菌体外增菌的影响

采用比浊法和活菌计数法研究在基础培养基/菊芋汁基础培养基中添加不同量低聚木糖、低聚果糖、红参提取液及其酸水解物对鼠李糖乳杆菌AS 1.2466T/保加利亚乳杆菌ATCC 11842生长情况的影响。结果表明:不同添加物对鼠李糖乳杆菌AS 1.2466T的增菌效果为红参提取液>红参酸水解物>低聚木糖>低聚果糖。当红参提取液添加量为12.50%时,鼠李糖乳杆菌AS 1.2466T的最大OD600值为1.172,活菌数为2.72×10^8 CFU/mL,比基础培养基中最大活菌数7.75×10^7 CFU/mL增加1个数量级。对保加利亚乳杆菌ATCC 11842的增菌效果为红参提取液>低聚木糖>红参酸水解物>低聚果糖。当红参提取液添加量为6.25%时,保加利亚乳杆菌ATCC 11842的最大OD600值为0.627,活菌数为4.43×10^8 CFU/mL,比菊芋汁基础培养基中最大活菌数1.48×10^7 CFU/mL增加1个数量级。红参提取液比低聚木糖、低聚果糖具有较好的增菌效果,将红参作为益生元研究其益生功能,为研究红参对肠道微生物的影响提供试验依据。     

保加利亚乳杆菌超浓缩培养及生化代谢规律的研究

应用改良MRS培养基对保加利亚乳杆菌进行了超浓缩培养,在培养过程中,采用了离心式半连续培养技术,并对二次培养后的培养基进行了改良,最终使菌体浓度达到1.045×1010cfu/mL.测定了保加利亚乳杆菌超浓缩培养过程中各种生化代谢规律的变化,包括菌体细胞的生长曲线、乳酸脱氢酶活力、氨基酸含量、脂肪酶活力的变化和培养液中乳酸脱氢酶活力、乳酸含量、氨基酸含量、葡萄糖含量、总蛋白含量、胆固醇含量、甘油三酯含量的变化.结果表明:在超浓缩培养过程中,去除代谢产物和添加底物可以明显地提高菌体的数量.     

酸乳发酵菌种抗湿热保护剂的研究

研究了8种物质对嗜热链球菌和保加利亚乳杆菌在湿热环境下存活率的影响。结果表明，脱脂奶粉、甘油、蔗糖、葡萄糖、海藻酸钠是较好的抗湿热保护剂。通过正交实验表明，复合保护剂效果优于单一保护剂。     

Retention of β-galactosidase activity in crude cellular extracts from Lactobacillus delbrueckii ssp. bulgaricus 11842 upon drying

Crude cellular extracts (CCEs) containing active β-galactosidase from Lactobacillus delbrueckii ssp. bulgaricus 11842 were spray-dried at three different outlet air temperatures (45, 55 or 65°C) or freeze-dried, with or without whey proteins, casein, whey or skim milk as drying adjuncts. The use of whey or skim milk resulted in significantly ( P   <  0.05) higher β-galactosidase activity retention in comparison to all other CCEs. This effect was not related to the initial total solids (TS) content (4–10%) of the feedstock solutions, but was presumably caused by the presence of lactose in the whey or skim milk CCE preparations.     

保加利亚乳杆菌富集锌的条件研究

研究了保加利亚乳杆菌将无机态微量元素锌富集转化为细胞内的有机态微量元素锌的条件。正交实验结果表明,培养基中ZnSO4浓度为主要影响因素,培养温度、培养时间和接种量为次要影响因素,其中又以培养温度的影响较主要。最佳富集条件为,ZnSO4浓度400μg/mL、培养温度37℃、培养时间36 h、接种量5%。在优化条件下,细胞富集的锌含量有明显升高,为249.8μg/g,有机态锌占总量的80%以上。     

保加利亚乳杆菌增菌条件的初步研究

从缓冲体系及增菌物两个角度对保加利亚乳杆菌增菌效果进行了研究。实验结果表明 10 %柠檬酸 (钠 ) ,5 %乙酸(钠 )及 2 %丙酮酸钠按一定比例构成的复合缓冲体系效果显著 ,并且在此体系基础上 5 0 %海带汁添加量为 2 0 %时具有叠加效应     

弱后酸化酸奶发酵剂的筛选

酸奶在贮存、运输、销售、食用前这一过程中发生后酸化现象,酸奶后酸化现象导致的结果是酸奶无法长期贮存,酸奶贮存期短的缺陷困扰着酸奶的消费。控制酸奶后酸化的措施有很多种,最好的控制措施是选育在高温条件下产酸较强、在低温条件下产酸甚微的菌株作为发酵剂。在以前研究的基础上,对几种有潜力的酸奶发酵剂进行了初步研究,发现汉森公司的YF-L812发酵的酸奶后酸化程度很小,在6℃条件下贮存30d时酸度仅上升了14.5°T。     

高清除自由基能力保加利亚乳杆菌ZS-2的诱变选育

分别对保加利亚乳杆菌ZS-2（LZS-2）进行紫外线诱变、硫酸二乙酯诱变及复合诱变，测定了突变株无细胞提取物清除DPPH自由基的能力。从诱变后的菌株中筛选出了3株对DPPH自由基清除率较高的乳酸菌UV2—6，UV5—4和D30—UV3—1。结果表明，保加利亚乳杆菌ZS-2分别经过紫外线诱变、DES、复合诱变后，选育出的突变菌株无细胞提取物对DPPH自由基清除率为56．43％，55．77％和55．60％，比出发菌株的清除率都提高了9％以上。     

The effect of Lactobacillus delbrueckii subsp bulgaricus proteinase on properties of milk gel acidified with glucono-δ-lactone

Lactobacillus delbrueckii subsp. bulgaricus CH9-3 proteinase is an enzyme that plays an important role in yogurt fermentation, by which its use is linked to gel properties of yogurt. In this work, a modified glucono-δ-lactone (GDL) acidification model was used to simulate the fermentation of yogurt and study the effect of CH9-3 proteinase on GDL-acidified milk gel. The results showed that the proteinase significantly improved the quality of milk gel by increasing its firmness, consistency, and viscosity index, while decreasing its syneresis. Furthermore, the proteinase could accelerate the formation of milk gel as indicated by the decrease in surface charge of milk gel. The findings demonstrate that CH9-3 proteinase has a positive effect on the properties of milk gel, and thus may have promising applications in the yogurt making industry.