Lactic acid bacteria (LAB) are industrially important bacteria that are widely used in the fermented food industry, especially in the manufacture of yogurt. Characteristic flavors are produced by LAB during fermentation and storage that affect the quality and acceptability of fermented milk products. In this study, the volatile compounds in milk fermented by Streptococcus thermophilus IMAU80842 alone, Lactobacillus delbrueckii ssp. bulgaricus IMAU20401 alone, or both species together were identified using solid-phase microextraction methods coupled with gas chromatography-mass spectrometry. A total of 53, 43, and 32 volatile compounds were identified in milk fermented by S. thermophilus alone, L. delbrueckii ssp. bulgaricus alone, or both species together, respectively. The presence of some important flavor compounds was confirmed: acetic acid, acetaldehyde, acetoin, 2,3-butanedione, ethanol, and 1-heptanol. Our results demonstrate that the composition of the volatile compounds in fermented milk depends on the species of LAB used and whether they are used alone or in combination. This is important for the selection of appropriate starter cultures for the production of different types of fermented milk product with particular flavors.

Background: There is increasing evidence to suggest an immunomodulation function both within the intestines and systemically upon consuming probiotic species. We recently isolated a novel LAB, Lactobacillus caseiZhang (LcZhang) from koumiss. LcZhang exhibited favorable probiotic properties, such as acid resistance, bile resistance, gastrointestinal (GI) colonization ability, etc. In order to examine the immunomodulatory qualities of LcZhang, we administered LcZhang to healthy mice with varying doses of either live or heat-killed LcZhang and measured various parameters of the host immune response.

This is the first study on the bacterial and fungal community diversity in 17 tarag samples (naturally fermented dairy products) through a metagenomic approach involving high-throughput pyrosequencing. Our results revealed the presence of a total of 47 bacterial and 43 fungal genera in all tarag samples, in which Lactobacillus and Galactomyces were the predominant genera of bacteria and fungi, respectively. The number of some microbial genera, such as Lactococcus, Acetobacter, Saccharomyces, Trichosporon, and Kluyveromyces, among others, was found to vary between different samples. Altogether, our results showed that the microbial flora in different samples may be stratified by geographic region.

Tarag is a characteristic fermented dairy product with rich microflora (especially lactic acid bacteria), developed by the people of Mongolian nationality in Inner Mongolia of China and Mongolia throughout history. One hundred and ninety-eight samples of Tarag were collected from scattered households in Eastern Inner Mongolia, and total of 790 isolates of lactic acid bacteria (LAB) were isolated by traditional pure culture method. To identify these isolates and analyze their biodiversity, 16S rRNA gene sequences analysis and PCR-DGGE were performed respectively. The results showed that 790 isolates could be classified as 31 species and subspecies. Among these isolates, Lactobacillus helveticus (153 strains, about 19.4%), Lactococcus lactis subsp. lactis (132 strains, about 16.7%) and Lactobacillus casei (106 strains, about 11.0%) were considered as the predominated species in the traditional fermented dairy products (Tarag) in Eastern Inner Mongolia. It was shown that the biodiversity of LAB in Tarag in Inner Mongolia was very abundant, and this traditional fermented dairy product could be considered as valuable resources for LAB isolation and probiotic selection.

Streptococcus thermophilus strain ND03 is a Chinese commercial dairy starter used for the manufacture of yogurt. It was isolated from naturally fermented yak milk in Qinghai, China. We present here the complete genome sequence of ND03 and compare it to three other published genomes of Streptococcus thermophilus strains.Streptococcus thermophilus strain ND03 was isolated from naturally fermented yak milk in Qinghai, China (10). It has many excellent processing properties, such as flavor, acidity, viscosity, and water holding. This strain has been implemented in the industrial production of dairy starter cultures by Inner Mongolia Yili Industrial Group Company, Ltd., the largest dairy corporation in China.Whole-genome sequencing of S. thermophilus strain ND03 was performed with a combined strategy of 454 sequencing (9) and Solexa paired-end sequencing technology (1). Genomic libraries containing 3-kb inserts were constructed, and 124,126 paired-end reads and 28,120 singleend reads were generated using the GS FLX system, giving 20.5-fold coverage of the genome. The majority (93.5%) of reads were assembled into seven large scaffolds, including 86 nonredundant contigs, using the 454 Newbler assembler (454 Life Sciences, Branford, CT). A total of 5,647,930 reads (2.5-kb library) were generated to reach a depth of 163-fold coverage with an Illumina Solexa GA IIx (Illumina, San Diego, CA) and mapped to the scaffolds using BurrowsWheeler alignment (BWA) (7). The gaps between scaffolds were filled by sequencing PCR products using an ABI 3730 capillary sequencer. The genome analysis was performed as described previously (4, 5).The complete genome sequence of ND03 contains a circular 1,831,957-bp chromosome with a GC content of 39.1%. There are 2,038 genes in total, including 1,919 coding genes, five rRNA operons, and 56 tRNAs in the ND03 genome.Comparison of the LMG18311 (2), CNRZ1066 (2), LMD-9 (8), and ND03 genomes revealed that they were highly similar, with the exception of 73 encoding genes that are uniquely present in ND03 but not in the other three strains. Some of the unique genes formed six large insertion islands that were comprised by transposase, glutamate decarboxylase, acetyltransferase, glycosyltransferase, polysaccharide biosynthesis protein, and the exopolysaccharide (EPS) biosynthesis gene cluster.Similar to other dairy bacteria, S. thermophilus is able to synthesize EPSs that lead to an improvement in the viscosity and texture of yogurt (3). The ND03 genome carries a unique 23.4-kb EPS gene cluster (STND_1010 to STND_1035), which contains 10 EPS-related genes and six intact or truncated insertions (IS). Four of the EPS-related genes in the cluster, epsA, epsB, epsC, and epsD, were conserved between all four genomes in comparisons. These genes are involved in the regulation, polymerization, and chain length determination and export of the EPS. The remaining six genes (epsE, epsF, epsG, epsI, epsJ, and epsP) in the EPS gene cluster were uniquely present in ND03 and regarded as the key enzymes to determin...

Previously, we demonstrated that the flavor of milk fermented with Lactobacillus delbrueckii subsp. bulgaricus (IMAU20401) and Streptococcus thermophilus (IMAU40133) at a 1:1000 ratio was superior to that of other ratios of the two strains. In this study, Lactobacillus plantarum P-8 was used as the probiotic bacterium. Six ratios (1:1, 1:5, 1:10, 1:50, 1:100, and 1:1000) of L. plantarum P-8 to yogurt starter were evaluated. A total of 66 volatile compounds including aldehydes, ketones, acids, alcohols, esters, alcohols, and aromatic compounds were identified in milk fermented with the six different L. plantarum P-8 to yogurt starter ratios at 0 d of storage. In particular, key flavor compounds, such as 3-methylbutanal, hexanal, (E)-2-octenal, nonanal, 2-heptanone, 2-nonanone, and acetoin, were identified in the 1:100 ratio treatment. Furthermore, the viable cell count, pH, titratable acidity, viscosity, and syneresis of the milk samples were analyzed during fermentation over 14 d of storage at 4°C. The results indicated that milk can be fermented with L. plantarum P-8 in combination with S. thermophilus and L. delbrueckii subsp. bulgaricus, and the physicochemical characteristics of the milk were not affected by the probiotic bacteria.

No abstract

No abstract