Biopreservative and Antioxidant Potential of Novel Lactic Acid Bacteria Strains from Low-Sodium Vegetable Fermentations

The growing consumer demand for functional foods containing natural preservatives has sparked renewed interest in spontaneous lactic acid fermentation. However, the effectiveness of this process, particularly under low-sodium conditions, needs to be better understood to ensure microbiological safety and functional benefits. This study aimed to evaluate microbial changes during the fermentation of five vegetables (green pepper, tomato, aubergine, carrot, and cabbage) and characterise isolated lactic acid bacteria (LAB) for their biopreservative and functional properties. The vegetables were fermented in brines with NaCl concentrations of 0%, 0.5%, 1%, and 3% for 45 days. Microbial growth was monitored and LAB isolates were screened for antimicrobial activity against Listeria monocytogenes and Staphylococcus aureus. Promising isolates were characterised further using physiological, biochemical, and antioxidant (DPPH) assays, and taxonomic identification was performed via API 20 STREP and 16S rDNA sequencing. The results showed that fermentation effectively suppressed Escherichia coli and S. aureus populations within 15 days in most samples. Eight selected LAB isolates, which were all catalase-negative Gram-positive cocci, showed strong inhibitory activity against both pathogens. These strains displayed significant tolerance to salinity (6.5% NaCl), alkaline conditions (pH 9.6), and thermal stress (60 °C for 30 min). Antioxidant assays revealed DPPH radical scavenging activity ranging from 27% to 65% at a concentration of 10⁹ CFU/mL. The dominant isolates were identified as Leuconostoc spp., and Lactococcus lactis. Notably, 16S rDNA sequencing confirmed that strain L11, isolated from tomato fermented for 11 months, belongs to Enterococcus faecium. This study confirms that low-sodium spontaneous vegetable fermentation can serve as a reliable source of multifunctional LAB, with promising applications as a biopreservative and probiotic starter culture in functional food production.