Influence of encapsulation on the survival of probiotics in food matrix under simulated stress conditions

The main objective of the present study was to evaluate the influence of encapsulation by extrusion technique using two hydrogels, namely; sodium alginate (Na-ALG) and whey protein isolate (WPI) on Bifidobacterium bifidium viability and stability of yoghurt under simulated gastrointestinal conditions. Probiotic bacteria (free or encapsulated) were added to yogurt for four weeks to test their viability and stability. Physicochemical and sensory analysis of yoghurt were conducted. Viability of B. bifidium in the simulated gastrointestinal conditions pH 2 and pH 7.5 was determined. Also, the efficiency of encapsulated final yield of the microcapsules was determined. With storage time, the pH of yoghurt containing encapsulated bacteria increased more than that of yoghurt containing free probiotic bacteria, resulting in a decrease in acidity. When compared to yoghurt containing encapsulated bacteria, the lactose level of yoghurt containing free probiotic bacteria decreased over time. The viscosity of yoghurt containing encapsulated WPI remained stable over the storage period, with syneresis remaining stable. The sensory properties of yoghurt containing free probiotics deteriorated over time. Cell viability was significantly reduced in yoghurt-containing free probiotics compared to other treated yoghurts. Cell viability in free probiotics yoghurt was lower than in encapsulated ones when exposed to simulated gastric and intestinal juice. In conclusion, WPI- encapsulated probiotics showed better stability over 28 days of storage in both yoghurt and gastrointestinal conditions, followed by sodium alginate.     

Complete genome sequencing of exopolysaccharide-producing Lactobacillus plantarum K25 provides genetic evidence for the probiotic functionality and cold endurance capacity of the strain

Lactobacillus plantarum (L. plantarum) K25 is a probiotic strain isolated from Tibetan kefir. Previous studies showed that this exopolysaccharide (EPS)-producing strain was antimicrobial active and cold tolerant. These functional traits were evidenced by complete genome sequencing of strain K25 with a circular 3,175,846-bp chromosome and six circular plasmids, encoding 3365 CDSs, 16 rRNA genes and 70 tRNA genes. Genomic analysis of L. plantarum K25 illustrates that this strain contains the previous reported mechanisms of probiotic functionality and cold tolerance, involving plantaricins, lysozyme, bile salt hydrolase, chaperone proteins, osmoprotectant, oxidoreductase, EPSs and terpenes. Interestingly, strain K25 harbors more genes that function in defense mechanisms, and lipid transport and metabolism, in comparison with other L. plantarum strains reported. The present study demonstrates the comprehensive analysis of genes related to probiotic functionalities of an EPS-producing L. plantarum strain based on whole genome sequencing.     

Monospecies and multispecies probiotic formulations produce different systemic and local immunostimulatory effects in the gilthead seabream (Sparus aurata L.)

The effects of the oral administration of heat-inactivated Lactobacillus delbrüeckii ssp. lactis and Bacillus subtilis, individually or combined, on gilthead seabream immune responses were investigated both systemically and locally in the gut. In a first experiment, seabream (65 g) were fed for 3 weeks different diets supplemented with 1 x 10(7)CFU g(-1)Lactobacillus, 1 x 10(7)CFU g(-1)Bacillus, or 0.5 x 10(7)CFU g(-1)Lactobacillus plus 0.5 x 10(7)CFU g(-1)Bacillus. Controls were fed non-supplemented diet. Six fish per group were sampled at the end of the trial and some humoral and cellular systemic innate immune parameters were evaluated. Feeding the mixture of the two killed bacteria species significantly increased natural complement, serum peroxidase and phagocytic activities compared with controls. In a second experiment, juvenile seabream (13 g) were fed for 3 weeks the same experimental diets and total serum IgM and numbers of gut IgM(+) cells and acidophilic granulocytes were evaluated. All these parameters were significantly higher in the multispecies probiotic group compared to monospecies and control fed groups. The advantages provided by administration of killed probiotic bacteria as well as multispecies versus monospecies formulations are discussed in light of the results obtained and for their possible application in aquacultural practices.     

Molecular characterization of alanine racemase from Bifidobacterium bifidum

Bifidobacterium bifidum is a useful probiotic agent exhibiting health-promoting properties, and its peptidoglycans have the potential for applications in the fields of food science and medicine. We investigated the bifidobacterial alanine racemase, which is essential in the synthesis of -alanine as an essential component of the peptidoglycans. Alanine racemase was purified to homogeneity from a crude extract of B. bifidum NBRC 14252. It consisted of two identical subunits with a molecular mass of 50 kDa. The enzyme required pyridoxal 5′-phosphate (PLP) as a coenzyme. The activity was lost in the presence of a thiol-modifying agent. The enzyme almost exclusively catalyzed the alanine racemization; other amino acids tested, except for serine, were inactive as substrates. The kinetic parameters of the enzyme suggested that the B. bifidum alanine racemase possesses comparatively low affinities for both the coenzyme (9.1 μM for PLP) and substrates (44.3 mM for -alanine; 74.3 mM for -alanine). The alr gene encoding the alanine racemase was cloned and sequenced. The alr gene complemented the -alanine auxotrophy of Escherichia coli MB2795, and an abundant amount of the enzyme was produced in cells of the E. coli MB2795 clone. The enzymologic and kinetic properties of the purified recombinant enzyme were almost the same as those of the alanine racemase from B. bifidum NBRC 14252.     

蒙古国地区酸乳中乳酸菌的鉴定及耐酸菌株筛选

本研究对采集自蒙古国地区牧民家庭中17份发酵乳样品中的乳杆菌进行了分离、鉴定、生物学特性和耐酸性研究。共分离出45株乳杆菌。通过形态观察、生理生化试验、糖发酵试验及16S rDNA序列分析等研究将这些菌株鉴定为Lactobacillum fermentum(L. fermentum)31 株, L. helveticus 12株, L. plantarum 1株 和L. casei 1株, 所以认为L. fermentum是蒙古国地区传统酸乳中的优势菌群。经pH 为3.0 的人工胃液耐受性试验复筛后发现, 存活率在80%以上的仅1株, IMAU20085的存活率高达81.44%。菌株的分离鉴定以及高耐酸性菌株的筛选, 对我国益生菌资源的保藏和开发有重要的意义, 对我国未来益生菌的开发具有重要价值。     

Enhancement of growth rate and β-galactosidase activity, and variation in organic acid profile of Bifidobacterium animalis subsp. lactis Bb 12

The behavior of Bifidobacterium animalis subsp. lactis Bb 12 under batch cultivation, after continuous culturing for up to 12 d, was monitored in skim milk-based media. Previous continuous culture for longer than 6 d affected the physiology of said microorganism. The minimum inhibitory concentrations of lactic and acetic acids increased from 18 to 26 g/l, whereas the molar ratio of acetic to lactic acid increased from 0.8 to 1.55, when the previous continuous culture increased its duration from 1 to 12 d. The specific lactose consumption rate decreased from 0.94 to 0.77 g_lactose/g_{cell dry mass}/h within the batch culture timeframe; this was concomitant with greater amounts of acetic and formic acids, and lower amounts of lactic acid produced. The β-galactosidase activity increased as continuous culturing time increased, and reached 446 units/ml by 12 d; however, the rate of enzyme synthesis decreased concomitantly. Succinic acid was produced during the exponential growth and stationary phases of the batch culture, but the former at exponential growth phase was higher as the continuous culturing time was longer. For comparison purposes, batch cultivation of samples taken from continuous cultures by 1 and 12 d was done using a semi-synthetic medium with glucose as carbon source; a pattern similar to that observed when using skim milk-based media was observed.     

Structural studies of the exopolysaccharide consisting of a nonasaccharide repeating unit isolated from Lactobacillus rhamnosus KL37B

A novel structure of exopolysaccharide from the lactic acid bacteria (LAB) Lactobacillus rhamnosus KL37B, from the human intestinal flora, is described. During the structural investigation of the exopolysaccharide it was found that the repeating unit is a nonasaccharide, which is the largest repeating unit found in LAB exopolysaccharides to date. The polysaccharide material was prepared by TCA extraction of a bacterial cell mass, purified by anion-exchange and gel permeation chromatography and characterized using chemical and enzymatic methods. On the basis of monosaccharide and methylation analysis and also 1D and 2D ¹H and ¹³C NMR spectroscopy the exopolysaccharide was shown to be composed of the following nonasaccharide repeating unit:The physicochemical cell surface study and adhesive properties indicated distinct surface properties of Lactobacillus rhamnosus strain KL37B with high adhesive abilities to Caco-2 cells, hydrophobicity and slime production, in comparison to other Lactobacillus strains used as controls.     

Development and validation of a new in vitro assay for selection of probiotic bacteria that express immune-stimulating properties in chickens in vivo

Oral administration of immunoprobiotic bacteria may support animal health. Species specificity of such microorganisms requires appropriate selection. An in vitro assay for the selection of immunoprobiotic lactic acid bacteria was developed in chicken. The assay allowed testing of large numbers of individual strains. Immune stimulation in vitro correlated well with the in vivo situation in two experiments and no false negative results occurred. Therefore this assay is an appropriate selection tool for immunomodulating properties of lactic acid bacteria in chicken.     

乳酸杆菌S-层蛋白性质及其益生功能研究进展

乳酸杆菌为应用最早、研究最多的益生菌种之一,能够调节肠道微生物区系的平衡,增强机体的免疫力和抵抗力。S-层蛋白在乳酸杆菌黏附过程中起重要作用,因此乳酸杆菌中的S-层蛋白成为研究热点。本文对乳酸杆菌S-层蛋白的结构、分离提纯方法、基因克隆情况和益生功能做了详细阐述。