Protease Sensitivity and Stress Adaptation of Bioactive Peptide-Producing Lactic Acid Bacteria: Functional Implications for Food Biopreservation

Background The search for safe, natural food preservatives has turned attention to antimicrobial peptide (AMP)-producing lactic acid bacteria (LAB). These AMPs, which are bioactive peptides of proteinaceous nature, inhibit a broad spectrum of foodborne pathogens. Their proteinaceous composition ensures safety and digestibility; however, their effectiveness depends on the physiological resilience of the producing LAB under food-relevant stresses and the susceptibility of the AMPs to proteolytic degradation. Results The 13 AMP-producing LAB strains tolerated a wide pH range (4.5–8.5), multiple temperatures (20–45°C), and moderate to high salt concentrations (5.5–10% NaCl), demonstrating robustness under diverse food processing and storage conditions. Even after exposure to these physiological stresses, the strains retained antimicrobial activity, producing zones of inhibition ranging from 5 mm under extreme stress conditions to 20 mm under optimum growth conditions against Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922. The antimicrobial peptides were completely inactivated by protease treatments with pepsin, trypsin, proteinase K, and papain, confirming their proteinaceous nature while highlighting protease susceptibility. Six of the 13 LAB strains had been previously 16S rRNA-sequenced (GenBank accession numbers PV983358–PV983363), including one novel strain showing 93.54% sequence identity to the closest known species; this strain is currently undergoing whole-genome sequencing, underscoring the rigor of prior molecular characterization and the potential for discovering novel antimicrobial producers. Conclusions AMP-producing LAB from Nigerian non-dairy fermentations exhibit broad physiological adaptability and produce proteinaceous antimicrobial peptides with notable inhibitory activity against foodborne pathogens, even under stress conditions. Although complete protease susceptibility limits in vivo stability, their safety, traceable identification, and environmental robustness underscore their promise as natural, clean-label food preservatives, supporting the development of safe, minimally processed food strategies.