Characterization of antifungal metabolites produced by novel lactic acid bacterium and their potential application as food biopreservatives

Fungal growth and mycotoxin production on foods and feeds cause poisoning and serious human diseases that may lead to death. Chemical preservatives and fungicides have negative impacts on both health and environment. In contrast, bio preservatives such as lactic acid bacteria (LAB) are effective, safe, biodegradable and have additional health benefits. Among 23 rod-shaped LAB strains that were isolated from Egyptian traditional fermented milk (Rayeb), strain RM1 showed the highest antifungal potency. Phylogenetic analysis based on complete 16S rRNA gene and unique phenotypic characteristics differentiated strain RM1 from the closely related Lactobacillus species suggesting it represents a novel species, for which the name Lactobacillus sp. RM1 is proposed. The cell-free supernatant (CFS) of Lactobacillus sp. RM1exhibited strong and broad antimicrobial activity against both toxigenic fungi and harmful bacteria. The chemical composition of CFS determined by GC–MS showed a wide variety of antioxidant and antimicrobial compounds. A complete inhibition of both aflatoxins B1 and ochratoxin A production was obtained at a CFS concentration of 15 mg/mL. When the CFS was used to treat wheat grains, the growth mycelia of Aspergillus parasiticus were completely inhibited after 2 weeks of incubation compared with untreated grains, which were covered with a mat of the fungus. The antifungal activity of Lactobacillus sp. RM1 against common toxigenic fungi, and its ability extend the shelf life of wheat grains prove its potential application as a natural preservative for food products.