Antifungal activity of Lactobacillus fermentum CRL 251

Abstract

Spoilage of food is mainly due to fungal growth. In addition to the great economic losses derived from the presence of mould, another concern is the potential mycotoxin production that may cause public health problems. In recent years, bio-preservation [the use of microorganisms and/or their metabolites to prevent spoilage and to extend the shelf life of foods] has gained increasing interest due to consumers? demands. Lactic acid bacteria (LAB) as bio-preservation organisms are of particular interest: they have been used for centuries as starter cultures in the food industry and are able to produce different kind of bioactive molecules, such as organic acids, peptides, fatty acids, hydrogen peroxide and bacteriocins. The present study was undertaken to evaluate the potentiality of Lactobacillus fermentum CRL 251 to inhibit mould and yeasts growth and characterize the metabolite/s involved. L. fermentumCRL 251 was grown in MRS broth (pH 6.5) at 37ºC for 24 h. The cell-free supernatants (CFS) was sterilized by filtration and used in the antifungal assays. The antifungal activity on various species of molds and yeasts was performed using the Microtitre Plate Well Assay. Conidial germination or yeast growth was determined during 48 h at 30ºC by measuring the optical density (OD580nm). The activity of CFS was determined in both neutral (pH 7, CFSn) and acidic (pH 3.8, CFSa) conditions. The activity of CFSn at different conditions of temperature (50, 100, 121ºC), pH range (3.0-8.0), and water activity (aw 0.995-0.901) was also determined. In addition, the effect of agitation on the antifungal compound/s production was evaluated. The resultsdemonstrated thatL.fermentum CRL 251 has inhibitory effect against a broad range of filamentous fungi (molds) and, to a greater extent, against spoilage yeasts in both, neutral and acidic conditions. The production of the antifungal compoundsstarts during the exponential phase and reaches the maximum value in the stationary phase where the activity (70-80 % inhibition)remained constant.The LAB growth under agitation condition not showedsignificant effect (p≤0.05) on the antifungal compounds production.The activity was stable during heat treatment and it remained constant even after autoclaving (121°C for 15 min). Maximum activity was determined at pH values between 3.0 and 5.0; at higher pH values no activity was observed. The inhibitory activity was stable at aw values between 0.995-0.937. No inhibitory activity was detected at awlower than 0.937. The antifungal peptides were partially purified and the molecular mass was estimated (approximately ≤ 10 kDa). This is the first report on a proteinaceous antifungal compound(s) productionby L. fermentum.