Secondary Metabolites of Novel Indigenous Lactic Acid Bacterial Strains as Biocontrol Agents of Tomato-Spoiling Bacteria

Tomato (Solanum lycopersicum) is highly susceptible to microbial spoilage, resulting in significant postharvest losses. The use of lactic acid bacteria (LAB) and their cell-free supernatants present a natural alternative to chemical preservatives in controlling spoilage bacteria. This study investigated the potential of indigenous LAB secondary metabolites as biocontrol agents against tomato-spoiling bacteria. LAB were isolated from Nigerian fermented foods (Iru, Ogi, and Nono), while spoilage bacteria were obtained from spoilt tomatoes using spread plate techniques. Secondary metabolites of LAB were obtained as cell-free supernatants through submerged fermentation and centrifugation, and their inhibitory activities were determined by the agar well diffusion method. Isolates showing activity were identified by 16S rRNA sequencing, and accession numbers were assigned. Several isolates belonging to Bacillus spp., Leuconostoc sp., and Lactobacillus spp. were recovered from fermented foods, while Bacillus spp., Escherichia coli, Salmonella sp., Pseudomonas aeruginosa, and Staphylococcus sp. were obtained from spoilt tomatoes. Five isolates exhibited inhibitory zones ranging from 3.10 ± 0.14 to 23.80 ± 0.07 mm and were confirmed as Bacillus subtilis (RNABASUIL01), Bacillus velezensis (RNABASUIL02), Lactobacillus acidophilus (RNABASUIL03), Lactiplantibacillus plantarum (RNABASUIL04), and Secundilactobacillus pentosiphilus (RNABASUIL05). Notably, this study is reporting for the first time the isolation of S. pentosiphilus from Nigerian fermented food, as well as the first evidence of antibacterial activity of secondary metabolites of Secundilactobacillus pentosiphilus. Among the tested isolates, the secondary metabolites of L. acidophilus RNABASUIL03 showed the strongest inhibitory activity and are therefore recommended as a promising natural preservative against tomato-spoiling bacteria.