Aims: This study aimed to characterize new isolates of human bifidobacteria, evaluate some of their probiotic potential and to screen these isolates for their effectiveness at inhibiting Listeria monocytogenes in vitro. Methods and Results: Thirty-four Bifidobacterium isolates from infant faeces were identified by fructose-6-phosphate phosphoketolase and PCR. Six isolates, coded RBL67, RBL68, RBL69, RBL70, RBL85 and RBL86, showed higher antagonistic activity against L. monocytogenes. Neutralized culture supernatants of these strains did not inhibit L. monocytogenes when tested by agar diffusion method. However, the concentration of supernatant by speed-vac resulted in the formation of an inhibitory effect with supernatants from strains RBL67, RBL68 and RBL70. This effect was shown to be related to heat-stable proteinaceous compound(s) which were resistant to heating at 100°C for 5 min but not to pronase-E, proteinase-K or trypsin. The extraction of the inhibitory compounds by methanol-acetone extraction procedure indicated that four strains (RBL67, RBL68, RBL69 and RBL70) were mostly soluble in acetone. However, strain RBL85 produced inhibitory substances that were soluble in methanol. Conclusion: Infant bifidobacterial isolates produce heat-stable proteinaceous compounds active against L. monocytogenes. Significance and Impact of the Study: Production of antibacterial substances by bifidobacteria would improve intestinal bacterial ecology and inhibit intestinal pathogens.

The effect on yogurt properties of in situ production of exopolysaccharides (EPS) and addition of 2 EPS powders (crude and purified EPS from Lactobacillus rhamnosus RW-9595M fermentation in whey-based medium) at different concentrations was studied. No effect of purified powder addition for EPS concentrations up to 500 mg/L was observed on acidification rate to the difference of milks supplemented with crude EPS, which exhibited longer acidification times. The addition of EPS from 125 to 500 mg/L or the use of EPS-producing cultures resulted in yogurts with lower yield stress and viscoelastic moduli compared with control yogurts without EPS, with no apparent effect of EPS concentration. However, the consistency index was higher for yogurts produced with the commercial EPS-producing culture, and to a lesser extent with the mixed culture containing Lb. rhamnosus RW-9595M, compared with yogurts supplemented with EPS powders, which were not different from that for control yogurts. Our study showed that the mode of EPS incorporation in yogurts has a major effect on the rheological properties of the final product.

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The definitive version is available at ww3.interscience.wiley.comInternational audienceAims: To evaluate the sensitivity of 21 common intestinal bacteria to six antibiotics and three broad-spectrum bacteriocins (nisins Z and A and pediocin PA-1). Methods and Results: Neutralized cell-free culture supernatants containing active bacteriocins, and antibiotics were tested with the agar diffusion test and the disc-diffusion method, respectively. The tested intestinal strains showed high sensitivity to most antibiotics except for streptomycin and oxacillin. Nisins A and Z (8 lg per well) had similar activity spectra and inhibited all Gram-positive intestinal bacteria at different levels (except Streptococcus salivarius), with bifidobacteria (except Bifidobacterium breve and Bif. catenulatum), Collinsella aerofaciens and Eubacterium biforme being the most sensitive strains, but they were not active against Gram-negative bacteria. Surprisingly, none of the tested strains were inhibited by pediocin PA-1 (16 lg per well). Conclusion: Pediocin PA-1 which is very active against Listeria spp. and other food pathogens did not inhibit major intestinal species in the human intestine in contrast to both nisins A and Z. Significance and Impact of the Study: Our data suggest that pediocin PA-1 has potential to inhibit Listeria within the intestinal microbiota without altering commensal bacteria

This study aimed to evaluate the effects of incorporating liposome-encapsulated nisin Z, nisin Z producing Lactococcus lactis ssp. lactis biovar. diacetylactis UL719, or Lactobacillus casei-casei L2A adjunct culture into cheese milk on textural, physicochemical and sensory attributes during ripening of Cheddar cheese. For this purpose, cheeses were made using a selected nisin tolerant cheese starter culture. Proteolysis, free fatty acid production, rheological parameters and hydrophilic/hydrophobic peptides evolution were monitored over 6 mo ripening. Sensory quality of cheeses was evaluated after 6 mo. Incorporating the nisin-producing strain into cheese starter culture increased proteolysis and lipolysis but did not significantly affect cheese rheology. Liposome-encapsulated nisin did not appear to affect cheese proteolysis, rheology and sensory characteristics. The nisinogenic strain increased the formation of both hydrophilic and hydrophobic peptides present in the cheese water extract. Sensory assessment indicated that acidic and bitter tastes were enhanced in the nisinogenic strain-containing cheese compared to control cheese. Incorporating Lb. casei and the nisinogenic culture into cheese produced a debittering effect and improved cheese flavor quality. Cheeses with added Lb. casei and liposome-encapsulated nisin Z exhibited the highest flavor intensity and were ranked first for sensory characteristics.