Correlation between metabolites of lactic acid bacteria isolated from dairy traditional fermented Tunisian products and antifungal and antioxidant activities.

Abstract

The objective of this study is to identify and investigate the antifungal and antioxidant potential of lactic acid bacteria (LAB) isolated from traditional fermented products. In this work, a collection of LAB was isolated from traditional fermented products collected in four Tunisian regions. After first screening using the overlay method, seven bacterial strains were retained due to their high antifungal effect. Four strains of Limosilactobacillus fermentum were identified, one strain of Lacticaseibacillus paracasei, one strain of Lacticaseibacillus rhamnosus and one strain of Enterococcus faecium. The antifungal and the antioxidant potential of these bacteria were then evaluated. Bacterial strains were effective against six fungal strains with minimum inhibitory concentrations ranging from 25 to 100 mg/ml and minimum fungicidal concentrations ranging from 50 to 200 mg/ml. Cell-free supernatants of LAB were analysed by HPLC-DAD and LC-MS-qTOF-MS analysis. Results showed significant production of organic acids as well as several phenolic compounds. Correlation analysis confirmed that PLA and 1,2-dihydroxybenzene were positively correlated with antifungal potential. The results of the antioxidant activity highlighted an ABTS radical cation scavenging activity ranging from 49% to 57% and a DPPH trapping percentage ranging from 80% to 97%. Therefore, due to these characteristics, identified lactic acid bacteria strains have shown their effectiveness to perform as antifungal and antioxidant agents. Since microbial contamination is at the root of extensive losses in the food sector, the identified strains or their metabolites can potentially be used as additives to limit micro-organism spoilage in food products and increase their shelf life.