Abstract
Consumer's demand for naturally preserved food products is growing and the use of bioprotective cultures is an alternative to chemical preservatives or a complementary tool to hurdle technologies to avoid or delay fungal spoilage of dairy products. To develop antifungal cultures for the dairy product biopreservation, experiments were conducted both in vitro and in situ. Firstly, the antifungal activity of 32 strains of lactic acid bacteria (LAB) and propionibacteria was screened alone, and then on combinations based on 5 selected lactobacilli strains. This screening was performed in yogurt and cheese models against four major spoilage fungi previously isolated from contaminated dairy products (Penicillium commune, Mucor racemosus, Galactomyces geotrichum, and Yarrowia lipolytica). Selected combinations were then tested as adjunct cultures in sour cream and semi-hard cheeses produced at a pilot scale to evaluate their antifungal activity during challenge tests against selected fungal targets (P. commune, M. racemosus, and Rhodotorula mucilaginosa) and shelf life tests; and their impact on product organoleptic properties. The screening step allowed selecting two binary combinations, A1 and A3 composed of Lactobacillus plantarum L244 and either Lactobacillus harbinensis L172 or Lactobacillus rhamnosus CIRM-BIA1113, respectively. In situ assays showed that the A1 combination delayed the growth of P. commune, M. racemosus and R. mucilaginosa for 2–24 days on sour cream depending of the antifungal culture inoculum, without effect on organoleptic properties at low inoculum (106 colony-forming units (CFU)/mL). Moreover, the A1 and A3 combinations also delayed the growth of P. commune in semi-hard cheese for 1–6 days and 1 day, respectively. Antifungal cultures neither impacted the growth of starter cultures in both sour cream and cheese nor the products' pH, although post acidification was observed in sour cream supplemented with these combinations at the highest concentrations (2.107 CFU/mL). The combination of both in vitro and in situ screening assays allowed developing 2 antifungal combinations exhibiting significant antifungal activity and providing future prospects for use as bioprotective cultures in dairy products.
Highlights
Food spoilage by fungi is responsible for considerable food waste and economical losses
They corresponded to Lactobacillus rhamnosus CIRM-BIA1759 and Lactobacillus paracasei CIRM-BIA1761 isolated from the commercial culture CC1, while Lactobacillus plantarum CIRM-BIA1758 was isolated from the commercial culture CC2
Culture X1 corresponded to a 1:1 combination of the L. paracasei CIRM-BIA1759 and L. rhamnosus CIRMBIA1761 strains, while X2 corresponded to L. plantarum CIRMBIA1758 alone
Summary
Food spoilage by fungi (molds or yeasts) is responsible for considerable food waste and economical losses. Agri-food industries rely mainly on chemical preservatives to control microbial contaminant growth and extend the product shelf life, but a strong societal demand for less processed and preservative-free food has emerged, and additive regulations are constantly evolving to limit their use (Fuselli et al, 2012). The latter aspects, combined with the necessity to produce food products complying with high safety and quality standards, have led to the search for alternatives to the use of chemical preservatives. Among the explored natural alternatives, biopreservation, corresponding to use of microorganisms and/or their antimicrobial metabolites (Stiles, 1996), has recently attract much interest
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