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In the agri-food context, bioprotective cultures represent an interesting alternative to chemical preservatives. The aim of this study was to evaluate the in vitro and in situ antifungal activity of lactic acid bacteria (LAB) and propionibacteria against bakery product spoilage fungi. Firstly, the biodiversity of fungal contaminant in pound cakes and milk bread rolls, as well as the resistance to chemical preservatives of representative isolates (n = 21), were studied. Aspergillus and Eurotium species were the most dominant spoilage fungi and the most resistant towards the tested chemical preservatives. They were followed by Penicillium , Cladosporium and Wallemia spp. Secondly, an in vitro screening showed that the most active isolates against selected fungal targets belonged to the Leuconostoc spp., Lactobacillus reuteri and Lactobacillus buchneri groups among the 270 tested LAB, as well as to the Propionibacterium freudenreichi and Propionibacterium acidipropionici species for the 50 tested propionibacteria. Finally, in situ tests showed that cultures of isolates belonging to the Leuconostoc citreum , Lactobacillus sakei , Lactobacillus plantarum , Lactobacillus spicheri , L. reuteri and Lactobacillus brevis species could delay one or several target fungal growths after bakery product surface spraying. Moreover, different strain cultures led to delayed fungal growths after incorporation in milk bread rolls preparation. The combination of in vitro and in situ approaches allowed for the identification of bacteria exhibiting antifungal activity, providing future prospects for use as bioprotective cultures in bakery products.

International audience; Antifungal activity of lactic acid bacteria (LAB) has been observed in many food fermentation processes. Organic acids produced during the growth of these microorganisms play a major role in antagonism towards molds. The present study characterizes antifungal compounds produced during growth of Lactobacillus harbinensis K.V9.3.1Np that was previously isolated from raw cow milk and found to possess strong antifungal activities. A pH-controlled batch fermentation in enriched milk protein medium with immobilized cells of this bacterium was carried out in the presence of disrupted cells of Debaryomyces hansenii UBOCC-A-211003 and Kluyveromyces lactis UBOCC-A-212021. After seven days of fermentation, cell-free culture supernatants with robust antifungal activities against D. hansenii, Penicillium expansum and Penicillium roqueforti were obtained. These cell-free supernatants contained high amounts of organic acids such as lactic and acetic acids as well as hexanoic acid (9 mM), which the latter revealed to be the most efficient antifungal compound. The antifungal activity of hexanoic acid was influenced by the environmental conditions including the nature of the matrix and the pH. Under the conditions tested, even if organic acids were key antifungal agents, they were only part of a complex mixture of various molecules that acted in a synergistic manner. (C) 2013 Elsevier Ltd. All rights reserved.

Eleven antifungal Lactobacillus strains previously isolated from cow and goat milk were fully characterized using molecular and phenotypic methods. Their antifungal activities were tested in milk and yogurt, against fungal species (Debaryomyces hansenii, Kluyveromyces lactis, Kluyveromyces marxianus, Penicillium brevicompactum, Rhodotorula mucilaginosa and Yarrowia lipolytica) commonly involved in the spoilage of dairy products. The antifungal strains belonged to Lactobacillus paracasei, Lactobacillus rhamnosus, Lactobacillus zeae and Lactobacillus harbinensis species and showed different acidifying and growth capacities in milk. All tested Lactobacillus strains showed an antifungal activity in milk with strain-dependent activity spectra. Lb. harbinensis showed a very strong antifungal effect in yogurt by completely inhibiting all tested fungi as compared to control. The other tested strains were much less effective. It is the first time that the antifungal activity of Lb. harbinensis is described. This strain is a potential candidate for yogurt biopreservation.

A strain of an unidentified strictly anoxic, gram-postive, non-motile Ruminococcus-like bacterium was isolated from a human faecal sample. The organism used carbohydrates as fermentable substrates, produced acetate, succinate, and hydrogen as the major products of glucose metabolism, and possessed a G + C content of 43.3 mol%. The morphological and biochemical characteristics of the organism were consistent with its assignment to the genus Ruminococcus but it did not correspond to any recognized species of this genus. Comparative 16S rRNA gene sequencing showed the unidentified bacterium represents a previously unrecognised sub-line within the Clostridium coccoides rRNA group of organisms. The nearest relative of the unknown bacterium corresponded to Ruminococcus obeum but a 16S rRNA sequence divergence value of >3% demonstrated it represents a different species. Based on the presented findings a new species, Ruminococcus luti, is described. The type strain of Ruminococcus luti is BInIX(T) (DSM 14534T, CCUG 45635T).