Antifungal lactic acid bacteria combinations as biopreservation tool in dairy products

Food spoilage is a major issue for the food industry, leading to important food waste and economic losses. In the context of a growing consumers’ demand for clean label foods [1], antifungal cultures are of growing interest as an alternative to chemical preservatives or a complement tool to hurdle technologies. Our aim was to select effective antifungal cultures in fermented dairy products and to identify the compounds most likely involved in their activity. Lactic acid bacteria and propionibacteria strains were screened alone and in combinations in yogurt and cheese models against four major spoilage fungi (Penicillium commune, Mucor racemosus, Galactomyces geotrichum, and Yarrowia lipolytica). Two binary combinations of lactobacilli were then selected to be evaluated in situ as adjunct cultures in sour cream and semi-hard cheeses produced at the pilot scale, to evaluate i) their antifungal activity during both challenge tests and shelf life tests, and ii) their impact on organoleptic properties. Four chromatography methods were combined to analyse antifungal compounds.Two binary combinations, A1 and A3 composed of L. plantarum L244 associated with either L. harbinensis L172 or L. rhamnosus CIRM-BIA1113, respectively, were selected from the screening step. Both combinations showed antifungal activity during in situ assays, with a higher efficacy of the combination A1 and a higher overall activity in sour cream compared to cheese [2]. In sour cream, A1 delayed the growth of P. commune, M. racemosus and R. mucilaginosafor 2-24 days depending of the antifungal culture inoculum, without effect on organoleptic properties at low inoculum (106colony-forming units (CFU)/mL). In semi-hard cheese, A1 delayed the growth of P. commune for 1 to 6 days. Analyses of antifungal compounds revealed that 33 compounds were in significantly higher amount in at least one product inoculated with an antifungal culture compared to the controls [3]. They were present at concentrations below their minimum inhibitory concentration and thus could act in synergy. Our screening approach allowed developing two antifungal combinations that exhibit significant antifungal activity and provide future prospects for use as bioprotective cultures in dairy products. This extensive study also contributes to improve the knowledge about the action mode of antifungal lactobacilli