Injury Mechanisms of Lactic Acid Bacteria Starter Cultures During Spray Drying: A Review

Lactic acid bacteria (LAB) starter cultures can be processed by many drying techniques, among which spray drying has great potential. However, injuries of LAB during spray drying lead to a low survival rate. The microbial injuries of LAB during spray drying are specifically induced by dehydration inactivation, thermal inactivation, and balance between the two. To reduce the drying temperature, new drying techniques based on spray drying were tried; that is, low-temperature vacuum–spray drying and spray–freeze drying.     

Use of Dacid-, Dbile-, zacid-, and zbile-Values in Evaluating Bifidobacteria with Regard to Stomach pH and Bile Salt Sensitivity

ABSTRACT: The survival of bifidobacteria in simulated conditions of the gastrointestinal (GI) tract was studied based on the D- and z-value concept. Some Bifidobacterium spp. are probiotics that improve microbial balance in the human GI tract. Because they are sensitive to low pH and bile salt concentrations, their viability in the GI tract is limited. The D- and z-value approach was therefore adopted as a result of observing constant log-cell reduction (90%) when Bifidobacterium spp. were exposed to these 2 different stressing factors. Survivals of one strain each or 4 species of Bifidobacterium was studied at pH between 3.0 and 4.5 and in ox-bile between 0.15% and 0.60% for times up to 41 h. From the D_acid- and D_bile-values, the order of resistance to acid and bile was B. bifidum > B. infantis > B. longum > B. adolescentis. While the former 3 strains retained high cell viability at pH 3.5 (>5.5 log CFU/mL after 5 h) and at elevated bile salt concentration of 0.6% (>4.5 log CFU/mL after 3 h), B. adolescentis was less resistant (<3.4 log CFU/mL). The z_acid- and z_bile-values calculated from the D_acid- and D_bile-values ranged from 1.11 to 1.55 pH units and 0.40% to 0.49%, respectively. The results suggest that the D_acid-, D_bile-, z_acid-, and z_bile-value approach could be more appropriate than the screening and selection method in evaluating survival of probiotic bacteria, and in measuring their tolerance or resistance to gastric acidity and the associated bile salt concentration in the small intestine. Practical Application: The evaluation of the tolerance of bifidobacteria to bile salts and low pH has been made possible by use of D- and z-value concept. The calculated z_acid- and z_bile-values were all fairly similar for the strains used and suggest the effect of increasing the bile salt concentration or decreasing the pH on the D_acid- and D_bile-values. This approach would be useful for predicting the suitability of bifidobacteria and other lactic acid bacteria (LAB) as probiotics for use in real-life situations.     

Microbial diversity and stability during primary cultivation and subcultivation processes of Tibetan kefir

In this study, we have investigated the microbial diversity and stability in the Tibetan kefir during the primary cultivation and subcultivation processes via a combination of culture‐independent and culture‐dependent methods. According to the culture‐independent methods, the profiles of PCR‐DGGE (polymerase chain reaction–denaturing gradient gel electrophoresis) indicated that nine microbial species were predominant at different cultivation stages; seventy four isolates of seven predominant species were obtained and identified via the culture‐dependent methods. PCR‐DGGE further confirmed that Lactobacillus kefiranofaciens, Lactobacillus kefiri, Lactobacillus paracasei, Streptococcus thermophilus, Kazachstania unispora and Saccharomyces cerevisiae were the most dominant species in the Tibetan kefir during the process of primary cultivation, among which Lb. kefiri, Lb. paracasei and K. unispora showed relative strong stability during both the processes of primary cultivation and subcultivation. These findings suggested that some isolates of the three species possessed the potentiality of being used in the development of direct vat set (DVS) starters for the production of Tibetan kefir and the related products.     

酸与胆汁盐耐性双歧杆菌菌种的筛选

从婴儿粪便和药品中筛选到耐酸和胆汁盐的2株双歧杆菌菌种,分别命名为Bi.bifidumWN 04与Bi.longumGB 03.在pH值2.0条件下培养2h后再于胆汁盐质量浓度1.0g/dL的条件下培养2h.2株菌在pH值分别为2.0和3.0的50mmol/L的磷酸盐缓冲液中存活率较高;在胆汁盐质量浓度分别为0.25,0.5,1.0g/dL和2.0g/dL,pH值为6.8的50mmol/L磷酸盐缓冲液中存活率也较高,胆汁盐耐受性没有明显区别.在4℃保存于新鲜牛乳中,Bi.bifidumWN 04能够在8周内保持最高活菌数[lg(CFU/mL)>9],其它菌种活菌数[lg(CFU/mL)]<8.