Antimicrobial activity of lactic acid bacteria isolated from spontaneous sourdough based on ecological flours

Abstract

This study aimed to isolate and identify lactic acid bacteria (LAB) strains from spontaneously fermented sourdoughs prepared from different ecological flour types: einkorn wheat, corn flour, and rye flour, manufactured according to the traditional type I sourdough protocol. The study also evaluated their antibacterial and antifungal properties, which are key properties for industrial applications. Twenty LAB strains were isolated, and eight strains were identified to the species level using a semi-automated Biolog® Microbial Identification System. Three isolates (Lactobacillus brevis LM6, Lactobacillus fermentum LM3, and Lactobacillus coryniformis subs. coryniformis LM8) demonstrated versatile carbohydrate metabolism by producing gas when grown at 30 °C, thus revealing their heterofermentative characteristics. The strains were tested for antimicrobial properties using the agar well diffusion method against pathogenic bacteria Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, and Bacillus spizizenii. Most LAB strains exhibited antibacterial activity against the test microorganisms, particularly against B. spizizenii. The antifungal effects of LAB strains against Aspergillus brasiliensis, Penicillium crysogenum, and Mucor racemosus were also investigated. Only four LAB strains showed an inhibitory effect on the growth and development of fungi. P. chrysogenum was the most susceptible to the action of LAB strains, especially L. plantarum LM2, P. acidilactici LM5, and L. coryniformis LM8. These results revealed that LAB isolated from the spontaneous sourdough have promising antimicrobial and antifungal properties, making the ecological flour sourdough a good source of LAB with high potential to be used for obtaining single or mixted starter cultures.