Novel Antimicrobial Peptide Inhibits Foodborne Pathogens, Delays Milk Spoilage
Researchers have identified a novel antimicrobial postbiotic peptide derived from an environmental Lacticaseibacillus strain that demonstrated antibacterial and antibiofilm activity against several foodborne pathogens, as well as the ability to preserve pasteurized milk.
The study, published in Applied Food Research, characterized the peptide, designated Postbiotin-E8, and evaluated its antimicrobial efficacy, physicochemical stability, and ability to preserve refrigerated milk.
The researchers, affiliated with the Pravara Institute of Medical Sciences and Dr. Babasaheb Ambedkar Marathwada University in India, isolated the peptide from Lacticaseibacillus sp. E8, a bacterial strain recovered from fruit and vegetable waste soil.
Antibacterial and Antibiofilm Activity Against Foodborne Pathogens
Laboratory testing demonstrated that Postbiotin-E8 exhibited broad-spectrum antibacterial activity against both Gram-positive and Gram-negative foodborne pathogens, including Escherichia coli, Bacillus cereus, Staphylococcus aureus, and Salmonella Typhi.
In disk diffusion assays, the peptide produced inhibition zones measuring 19 millimeters (mm) against E. coli, 21 mm against B. cereus, and 23 mm against S. aureus.
Additional testing against S. aureus and S. Typhi demonstrated concentration-dependent growth inhibition and bactericidal activity. After 24 hours of exposure, no viable S. aureus colonies were detected at peptide concentrations of 31.25, 62.5, or 125 micrograms per milliliter (µg/mL). For S. Typhi, no viable colonies were detected at concentrations of 62.5 and 125 µg/mL.
Postbiotin-E8 also inhibited biofilm formation by both pathogens. At a concentration of 100 µg/mL, the peptide reduced biofilm formation by 58.7 percent for S. aureus and 67.68 percent for S. Typhi.
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The researchers also evaluated the peptide's stability under different environmental conditions. Postbiotin-E8 retained antimicrobial activity across a pH range of 4–8 and at temperatures up to 50 °C, as well as in the presence of certain detergents and organic solvents.
Postbiotin-E8 Delayed Spoilage in Refrigerated Milk
To evaluate its potential as a natural food preservative, the researchers added Postbiotin-E8 to pasteurized milk at a concentration of 100 µg/mL and monitored its quality during 10 days of refrigerated storage at 4 °C. The peptide's preservative efficacy was compared with untreated milk, a diluent control, and milk treated with nisin.
Compared with untreated milk, Postbiotin-E8-treated samples exhibited reduced microbial growth, greater pH stability, delayed visible spoilage, and improved sensory quality.
By day 10, the total viable microbial count in Postbiotin-E8-treated milk reached 3.83 log₁₀ colony-forming units per milliliter (CFU/mL), compared with approximately 4.1 log₁₀ CFU/mL in untreated controls. The treated milk also maintained a higher pH of 6.38, compared with approximately 6.0 in untreated samples.
Visible spoilage was observed in untreated milk beginning on day 5, whereas Postbiotin-E8-treated milk showed no visible changes through day 7. By day 10, the treated milk exhibited minimal turbidity and mild odor changes, compared with moderate turbidity and a slightly sour odor in untreated samples.
Although Postbiotin-E8 improved milk preservation, nisin demonstrated greater efficacy, producing lower microbial counts, better pH stability, and higher sensory quality scores throughout storage. Still, the researchers emphasized the peptide’s promise as a natural bio-preservative for extending the shelf-life of refrigerated milk.
Potential Applications and Future Research
Based on the findings, the researchers suggested that Postbiotin-E8 could have potential applications in food preservation and food-contact surface decontamination.
The researchers called for additional studies to determine the peptide's mechanism of action, evaluate its safety and cytocompatibility, and validate its efficacy in more complex food systems.
