The study, published in Frontiers in Industrial Microbiology, was conducted by Constanza Melian, Nora Bertola, Graciela Vignolo, and Patricia Castellano at the Centro de Referencia para Lactobacilos in Tucumán and the Centro de Investigación y Desarrollo en Criotecnología de Alimentos in La Plata. Their goal was to build a biodegradable, active packaging material that could protect chilled meat products without relying on synthetic preservatives or petroleum-based plastics.

The antimicrobial agent at the heart of the film is a bacteriocin, a ribosomally synthesized peptide produced by certain lactic acid bacteria. Lactocin AL705 is generated by Latilactobacillus curvatus CRL705, a strain originally isolated from traditional Argentine fermented sausages. This bacterium carries genes for two bacteriocins: lactocin 705, a two-component class IIb peptide, and lactocin AL705, a class IIa peptide with strong anti-listerial activity. Previous work by the same group showed that these bacteriocins could be adsorbed onto linear low-density polyethylene films and that wheat gluten films enriched with them prevented Listeria growth in wieners stored at 5 degrees Celsius for 45 days.

To build the new film, the researchers dispersed 2.8 percent high-methoxyl pectin in distilled water at 50 degrees Celsius, added glycerol as a plasticizer, and incorporated lactocin AL705 at three concentrations: 0.62, 1.25, and 2.50 milligrams per milliliter. The pH was adjusted to 3.0, and the film-forming solutions were cast onto Petri dishes and dried at 30 degrees Celsius. The minimum inhibitory concentration of lactocin AL705 against Listeria monocytogenes FBUNT was determined by broth microdilution following Clinical and Laboratory Standards Institute guidelines, yielding a MIC of 1.25 milligrams per milliliter, defined as the lowest concentration achieving at least 95 percent growth inhibition.

When the researchers tested the films on semi-solid agar plates inoculated with 10 to the sixth colony-forming units per milliliter of Listeria, films containing 1.25 and 2.50 milligrams per milliliter of the bacteriocin produced clear inhibition zones, while the lowest concentration showed no activity. This confirmed that the MIC concentration was sufficient to activate the film matrix.

Characterization of the films revealed a nuanced picture. The addition of lactocin AL705 did not significantly affect moisture content, color lightness, elongation at break, or tensile strength compared with control films. However, the active films exhibited progressively lower water vapor permeability as bacteriocin concentration increased, with the lowest value of 3.24 times 10 to the minus 10 grams per meter per second per Pascal observed at 2.5 milligrams per milliliter. The researchers attribute this reduction to the dispersion of bacteriocin particles within the pectin-glycerol matrix, which promotes intermolecular interactions that limit water molecule penetration. Opacity increased significantly at the highest bacteriocin concentration, and the films appeared slightly more yellowish, likely due to the intrinsic coloration of lactocin AL705.

Fourier transform infrared spectroscopy showed that the chemical structure of the pectin polymer remained unchanged after bacteriocin incorporation, with no new peaks or significant shifts in peak intensity. Scanning electron microscopy, however, revealed surface modifications: control films displayed a uniform and compact surface, while films containing the bacteriocin showed a rougher morphology without evidence of aggregation. The films also exhibited strong ultraviolet absorption in the UVC range of 200 to 280 nanometers, a desirable property for preventing oxidative deterioration in packaged foods.

The critical challenge test involved inoculating cooked ham slices with Listeria monocytogenes at approximately 10 to the fourth colony-forming units per milliliter, wrapping them in the active film, and storing them at 4 degrees Celsius for 14 days. Viable Listeria counts were undetectable at 0 and 7 days of incubation. Although the pathogen load increased toward day 14, reaching approximately 4.2 log colony-forming units per gram, it remained dramatically controlled compared with ham wrapped in control films or left unwrapped, which reached approximately 9.32 log colony-forming units per gram by the end of storage. A similar trend was observed at 10 degrees Celsius, the abuse temperature chosen to simulate temperature changes during commercial and domestic handling.

The implications of this work extend beyond the laboratory. Only nisin and pediocin PA-1/AcH are currently approved as food additives among bacteriocins, so evaluating new candidates in different matrices is essential for advancing functional antimicrobial packaging. Pectin, valued for its biodegradability, biocompatibility, non-toxicity, and low cost, offers a sustainable alternative to petroleum-based polymers. The researchers conclude that high-methoxyl pectin films incorporated with lactocin AL705 represent a promising alternative for functional food packaging aimed at improving the preservation of ready-to-eat refrigerated meat products, potentially offering the food industry a biodegradable shield against one of its most persistent pathogens.

Subject of Research: Edible pectin films with bacteriocin lactocin AL705 suppress Listeria in cooked ham

Article Title: Anti-listerial activity of active high-methoxyl pectin films incorporated with Latilactobacillus curvatus CRL705 bacteriocins: effectiveness assessment in ham

Article References: Melian, C., Bertola, N., Vignolo, G. M., & Castellano, P. (2026). Anti-listerial activity of active high-methoxyl pectin films incorporated with Latilactobacillus curvatus CRL705 bacteriocins: effectiveness assessment in ham. Frontiers in Industrial Microbiology, 4, Article 1826438. https://doi.org/10.3389/finmi.2026.1826438

Image Credits: AI Generated

DOI: 10.3389/finmi.2026.1826438

Keywords: Listeria monocytogenes, bacteriocin, lactocin AL705, high-methoxyl pectin, edible film, antimicrobial packaging, Latilactobacillus curvatus, food safety, ready-to-eat meat, biopreservation, cooked ham, biodegradable packaging