Covalent Grafting of 5-Aminolevulinic Acid onto Polylactic Acid Films and Their Photodynamic Potency in Preserving Salmon

Abstract

A novel photodynamic inactivation (PDI)-mediated antimicrobial film of polylactic acid/5-aminolevulinic acid (PLA/ALA) was successfully fabricated by a covalent grafting method using low-temperature plasma. The chemical structure, surface morphology, hydrophilic ability, and mechanical and barrier properties of the films were characterized, and their antibacterial, anti-biofilm potency and preservation effects on ready-to-eat salmon were investigated during storage. Results showed that the amino group of ALA was covalently grafted with the carboxyl group on the surface of PLA after the plasma treatment, with the highest grafting rate reaching ∼50%. The fabricated PLA/ALA films displayed an enhanced barrier ability against water vapor and oxygen. Under blue light-emitting diode illumination, the PLA/ALA films generated massive reactive oxygen species from the endogenous porphyrins in cells induced by ALA and then fatally destroyed the cell wall of planktonic cells and the architectural structures of sessile biofilms of the pathogens (Listeria monocytogenes and Vibrio parahaemolyticus) and spoilage bacterium (Shewanella putrefaciens). More importantly, the PDI-mediated PLA/ALA films potently inhibited 99.9% native bacteria on ready-to-eat salmon and significantly suppressed the changes of its drip loss, pH, and lipid oxidation (MDA) during storage, and on this basis, the shelf life of salmon was extended by 4 days compared with that of the commercial polyethylene film. Therefore, the PDI-mediated PLA/ALA films are valid in inactivating harmful bacterial and preserving the quality of seafood.

Nonmigrating Active Antibacterial Packaging: Antimicrobial Mechanism against Staphylococcus Aureus and Its Application in Large Yellow Croaker

“…For the modified grafted film, the antibacterial agent is relatively uniformly fixed on the film surface. The cross sections of the five groups of films were relatively uniform and showed no obvious difference, which indicated that plasma treatment and covalently bonded grafting only occurred on the surface, but not inside the film, which was also consistent with the study of Huang and Chen et al 18,33 CS (by covalent fixation) covered the surface of the PLA base film, and the CS layer was observed at the CS-g-PLA base film cross section. The CS layer had an average thickness of 1 μm.…”

Toxicity of Polymeric Nanodrugs as Drug Carriers

“…As a natural intermediary in carbohydrate biosynthesis, the biodegradable and biocompatible polymer PLA splits into monomeric units of lactic acid in the human body . Solvent evaporation, displacement, and diffusion have often been used to create PLA. − The salting-out process is characterized by the addition of compounds, such as MgCl 2 and CaCl 2 to separate them into water-miscible and immiscible solvent layers. The principal benefit of salting out is that it reduces the burden on protein capsules …”

New trends in the development of photodynamic inactivation against planktonic microorganisms and their biofilms in food system

“…Once the films are exposed to light, the PSs will not be artificially controlled and are easily excited and degraded to lose the antibacterial potency. For this consideration, Chen et al (2023) innovatively fabricated a smart PDI-mediated APF by covalently grafting the PS precursor of ALA onto the polylactic acid (PLA) film surface (Figure 7B). The surface of PLA film was immobilized with massive carboxyl groups (-COOH) using the low-temperature plasma.…”

“…For this consideration, Chen et al. (2023) innovatively fabricated a smart PDI‐mediated APF by covalently grafting the PS precursor of ALA onto the polylactic acid (PLA) film surface (Figure 7B). The surface of PLA film was immobilized with massive carboxyl groups (‐COOH) using the low‐temperature plasma.…”

“…As a result, the PDI‐mediated PLA/ALA film fatally destroyed the cell membrane of planktonic cells and the architectural structures of the sessile biofilms. More importantly, the film effectively reduced 99.9% of native bacteria on ready‐to‐eat salmon and potently extended the shelf life by 4 days (Chen et al., 2023). Therefore, the PDI‐mediated APF is novel and promising packaging in the food industry for ensuring the food safety.…”