Statistical Optimization and Partial Characterization of Bacteriocin Produced by Lactobacillus Fermentum Mt186600 Isolated from Fermenting African Oil Bean Seed

Abstract

Bacteriocins are antimicrobial peptides produced by bacteria and used as natural food biopreservatives. This study isolated lactic acid bacteria from fermenting African oil bean seed (Ugba), with antibacterial activity, identified the most promising producer, and optimized bacteriocin production using a one-parameter-at-a-time (OPAT) approach followed by response surface methodology (RSM). Out of 10 isolates recovered on de Man, Rogosa, and Sharpe (MRS) agar, only 1 (AOBS-10) exhibited antibacterial activity against both indicator organisms (Staphylococcus aureus ATCC 19095 and Escherichia coli ATCC 35218). AOBS-10 was identified by 16S rRNA gene sequencing as Lactobacillus fermentum (GenBank accession MT186600). OPAT screening identified sucrose as the most favorable carbon source (2959.25 AU/mL) and pH 7 as favorable, raising activity above the baseline of 2041.00 AU/mL. A four-factor central composite design (CCD) was used to model the combined effects of sucrose concentration, pH, NaCl concentration, and incubation period. The second-order model was highly significant (F = 26.13, p < 0.0001) with a coefficient of determination (R²) of 0.9606. The optimum conditions: 1.51% sucrose, 1.59% NaCl, pH 6.35, and 28.66 h incubation gave a predicted activity of 4051.55 AU/mL and an experimental activity of 4403.85 AU/mL, confirming model adequacy. The partially purified bacteriocin had an apparent molecular mass in the 13-35 kDa range, was stable between pH 5 and 8 and between 24 and 50 °C, with reduced activity at pH 9 and at 4 °C and 100 °C. These findings indicate that L. fermentum MT186600 is a promising source of a robust bacteriocin with potential application as a biopreservative.