A meta-analysis on the effectiveness of homofermentative and heterofermentative lactic acid bacteria for corn silage.

AIMS: This meta-analysis aims to assess the effect of lactic acid bacteria (LAB) inoculation on fermentation parameters, microbiological composition and aerobic stability of corn silage. METHODS AND RESULTS: Databases (PubMed, ScienceDirect and Scopus) were searched from 1980 to 2017. The criteria for inclusion were: randomized and controlled experiments using corn silage and published in peer-reviewed journals. The meta-analysis showed that LAB supplementation increased pH, acetate and propionate concentrations, and decreased acid detergent fibre, water-soluble carbohydrates and ammoniacal nitrogen (NH3 -N) compared to controls in the pooled raw mean difference random effect model. In addition, inoculation reduced counts of yeasts and moulds, increased LAB counts and markedly improved aerobic stability in corn silage. However, results indicated that the effect of inoculants may differ depending on the administration of homofermentative or heterofermentative LAB. CONCLUSIONS: For the development of functional bacterial inoculants, both types of LAB should be used. SIGNIFICANCE AND IMPACT OF THE STUDY: To our knowledge, this is the first meta-analysis to compare the application of homofermentative and heterofermentative LAB for corn silage.

Viability and resistance of lactobacilli isolated from cocoa fermentation to simulated gastrointestinal digestive steps in soy yogurt.

To study the potential probiotic characteristics such as decrease of pH, microbial viability, and tolerance to simulated digestive steps of fermented soy beverage ("soy yogurt") produced with lactobacilli isolated from cocoa fermentation (Lactobacillus fermentum TcUESC01 and Lactobacillus plantarum TcUESC02) during fermentation and refrigerated storage. The sensory acceptance of the yogurts was also tested. Samples of soy yogurt produced with L. fermentum TcUESC01 or L. plantarum TcUESC02 were collected during fermentation (0, 4, 8, and 12 h) and refrigerated storage (1, 9, 18, and 27 d), and submitted to pH and bacterial viability determinations. Tolerance to simulated digestion steps was done with refrigerated storage samples at 9 °C. Simulated digestion was performed in 3 successive steps: exposure to pepsin-HCl solution, bile shock, and simulated small intestinal juice. During storage, a decrease in pH and lactobacillus viability was observed. L. fermentum TcUESC01 showed to be more resistant than L. plantarum TcUESC02 to simulated gastrointestinal digestion. All soy yogurts showed acceptable hedonic scores (greater than 5 in a 9-point hedonic scale ranging from "like extremely" to "dislike extremely") in sensory evaluation for flavor, aroma, color, consistency, and overall impression. L. plantarum TcUESC02 and, especially, L. fermentum TcUESC01 showed potential probiotic characteristics when considering pH, cell viability, and tolerance to simulated digestive steps and did not affect the sensory characteristics when supplemented to soy yogurt during storage.

In vitro evaluation of Bifidobacterium strains of human origin for potential use in probiotic functional foods.

The present study investigated some in vitro properties for probiotic use of four strains of bifidobacteria isolated from faeces of healthy children (Bifidobacterium longum 51A, Bifidobacterium breve 1101A, Bifidobacterium pseudolongum 1191A and Bifidobacterium bifidum 1622A). In vitro tests were carried out to compare growth rate, aerotolerance, antagonistic activity against pathogens, antimicrobial susceptibility profile and cell wall hydrophobicity. Mean doubling time of B. longum 51A was shorter compared to the other strains. All strains were aerotolerant up to 72 h of exposure to oxygen. In vitro antagonism showed that B. longum 51A and B. pseudolongum 1191A were able to produce inhibitory diffusible compounds against all pathogenic bacteria tested, but not against Candida albicans. B. longum 51A was sensitive to all the antimicrobials tested, except neomycin. The hydrophobic property of the cell wall was highest for B. bifidum 1622A. Based on these parameters, B. longum 51A showed the best potential for probiotic use among the tested strains, presenting the greatest sensitivity to antimicrobials, the best growth rate and the highest capacity to produce antagonistic substances against various pathogenic microorganisms.

Relationship between interaction sites in the gut, hydrophobicity, mucosal immunomodulating capacities and cell wall protein profiles in indigenous and exogenous bacteria.

AIMS: To investigate whether there is a relationship between interaction sites in the gut, hydrophobicity, mucosal immunomodulating capacities and cell wall protein profiles in lactobacilli, bifidobacteria and enterococci. METHODS AND RESULTS: Hydrophobicity, cell wall protein profiles and sites of interaction in the gut (by using fluorescein isothiocyanate-labelled bacteria) were determined for Lactobacillus casei, L. acidophilus, L. fermentum, Bifidobacterium bifidum, B. animalis and Enterococcus faecalis. We also determined the number of immunoglobulin (Ig)A+, tumour necrosis factor (TNF)alpha+, interleukin (IL)-6+ and IL-10+ cells after oral administration of the above bacteria to BALB/c mice. All strains assessed were found to interact with the sites of induction of the immune response in the gut. No correlation with hydrophobicity was observed. When some strains at certain doses were administered to mice, bacterial translocation to liver was observed. The oral administration of indigenous (104 cells day(-1)) and exogenous (107 cells day(-1)) bifidobacteria and lactobacilli for 5 consecutive days activated the systemic and intestinal mucosal immune response in a strain-specific way, independently whether the strain was indigenous or exogenous in relation to the host. The differences in the immunopotentiating capacity of the various strains might be related to the differences in their cell wall protein profiles. CONCLUSIONS: Indigenous bacteria activated the mucosal immune response at a dose significantly smaller than the one required for probiotic exogenous bacteria. However, probiotic exogenous bacteria can be used at high concentrations in fermented dairy products with a great impact on the immune system, favouring its immunomodulation. SIGNIFICANCE AND IMPACT OF THE STUDY: The immunomodulation capacity of probiotic bacteria is strain specific and independent of the specificity of the host. The ability of certain strains to down-regulate the production and release of IL-6 by IL-10 may have potential implications in their use in cases in which cytokine deregulation or excessive production at the mucosal level can be the cause of tissue damage.

Interactions among lactic acid starter and probiotic bacteria used for fermented dairy products.

Interactions among lactic acid starter and probiotic bacteria were investigated to establish adequate combinations of strains to manufacture probiotic dairy products. For this aim, a total of 48 strains of Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lactococcus lactis, Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium spp. (eight of each) were used. The detection of bacterial interactions was carried out using the well-diffusion agar assay, and the interactions found were further characterized by growth kinetics. A variety of interactions was demonstrated. Lb. delbrueckii subsp. bulgaricus was found to be able to inhibit S. thermophilus strains. Among probiotic cultures, Lb. acidophilus was the sole species that was inhibited by the others (Lb. casei and Bifidobacterium). In general, probiotic bacteria proved to be more inhibitory towards lactic acid bacteria than vice versa since the latter did not exert any effect on the growth of the former, with some exceptions. The study of interactions by growth kinetics allowed the setting of four different kinds of behaviors between species of lactic acid starter and probiotic bacteria (stimulation, delay, complete inhibition of growth, and no effects among them). The possible interactions among the strains selected to manufacture a probiotic fermented dairy product should be taken into account when choosing the best combination/s to optimize their performance in the process and their survival in the products during cold storage.

Characterization and control of thread mould in cheese.

AIMS: The origin of a mould responsible for the contamination of an Argentinian cheese factory was identified and several antifungal treatments were assessed. METHODS AND RESULTS: Moulds were isolated and identified from vacuum-packed hard cheeses, from the environment and from the surfaces of the factory. A suspension conidia test containing different fungicides was performed; another assay involved the fumigation with p-OH fenilsalicidamide. Only Phoma glomerata was found in all of the mouldy cheeses, and was also obtained from different environments and machine surfaces. The most effective treatments against P. glomerata isolates were 0.5% (w/v) natamycin and 2% (v/v) parabens. Fumigation with p-OH fenilsalicidamide showed no satisfactory results. CONCLUSION: P. glomerata is an important thread mould-contaminating agent in vacuum-packed hard cheeses. SIGNIFICANCE AND IMPACT OF THE STUDY: Taking into account the survival of the conidia of the P. glomerata isolates to different antifungal treatments, the sources of contamination need to be controlled by designing a good factory layout.

Viability of probiotic (Bifidobacterium, Lactobacillus acidophilus and Lactobacillus casei) and nonprobiotic microflora in Argentinian Fresco cheese.

We evaluated the suitability of Argentinian Fresco cheese as a food carrier of probiotic cultures. We used cultures of Bifidobacterium bifidum (two strains), Bifidobacterium longum (two strains), Bifidobacterium sp. (one strain), Lactobacillus acidophilus (two strains), and Lactobacillus casei (two strains) in different combinations, as probiotic adjuncts. Probiotic, lactic starter (Lactococcus lactis and Streptococcus thermophilus), and contaminant (coliforms, yeasts, and molds) organisms were counted at 0, 30, and 60 d of refrigerated storage. Furthermore, the acid resistance of probiotic and starter bacteria was determined from hydrochloric solutions (pH 2 and 3) of Fresco cheese. The results showed that nine different combinations of bifidobacteria and L. acidophilus had a satisfactory viability (count decreases in 60 d <1 log order) in the cheese. Both combinations of bifidobacteria and L. casei cultures assayed also showed a satisfactory survival (counts decreased <1 log order for bifidobacteria but no decrease was detected for L. casei). On the other hand, the three combinations of bifidobacteria, L. acidophilus, and L. casei tested adapted well to the Fresco cheese environment. When a cheese homogenate at pH 3 was used to partially simulate the acidic conditions in the stomach, the probiotic cultures had an excellent ability to remain viable up to 3 h. At pH 2, the cell viability was more affected; B. bifidum was the most resistant organism. This study showed that the Argentinian Fresco cheese could be used as an adequate carrier of probiotic bacteria.