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Biopolymer Paperboard Impregnation Based on Chitosan and Nanocellulose with Addition of Caffeine and Gallic Acid
In this study, the preparation and detailed characterization of a chitosan (CHT) impregnation system modified with cellulose nanofibrils (CNFs) and enriched with bioactive compounds—caffeine (CAF) and gallic acid (GA)—applied to the surface of unbleached paperboard were described. Their mechanical properties (tensile strength, elongation at break, and bursting strength), structural features, and surface barrier parameters (water absorption) were evaluated. The antibacterial activity of the formulations comprising 1% chitosan (1% CHT), 1% chitosan with 1% caffeine (1% CHT/1% CAF), and 1% chitosan with 1% gallic acid (1% CHT/1% GA)—applied to enhance the functionality of the coated paperboard—was additionally assessed. The incorporation of cellulose nanofibrils into the coating matrix markedly improved the mechanical performance of the paperboard, particularly in terms of puncture resistance and elongation at break, while all modified coatings retained high burst strength. Impregnations containing gallic acid or caffeine showed similar mechanical characteristics but improved flexibility without compromising structural integrity. Chitosan solutions containing gallic acid and solutions containing caffeine exhibited activity against the tested Gram-positive (S. aureus, L. monocytogenes) and Gram-negative (E. coli, P. aeruginosa) bacterial strains. Antibacterial analysis showed moderate activity against Gram-positive strains and strong inhibition of Gram-negative bacteria, with the 1% CHT/1% GA impregnation giving the largest zone of growth inhibition around the sample—19 mm in the agar diffusion test—indicating the strongest suppression of E. coli. It was found that incorporation of nanocellulose into the chitosan matrix significantly reduces water uptake by treated paperboard surface, which is critical in the context of food packaging. The best result—Cobb60 value of 32.85 g/m2—was achieved for the 1% CHT/1% CNF formulation, corresponding to an 87% reduction in water absorption compared to the uncoated control. The results obtained in this study indicate a promising potential for the use of these impregnation systems in sustainable packaging applications.
Chitosan-Based Films with Essential Oil Components for Food Packaging
Chitosan-based films show great potential in terms of application in food preservation and are also promising carriers of biologically active ingredients. This paper presents the potential use of chitosan-based films with the addition of essential oil components, e.g., carvacrol, eugenol, and isoeugenol, intended for food packaging. The characteristics of the obtained films were determined, including antibacterial, mechanical, barrier, and structural parameters. In addition, the antibacterial and antioxidant effects of the essential oil components were assessed. Eugenol (44.41%) and isoeugenol (43.56%) showed high antiradical activities, similar to the activity of Trolox (44.33%), which is used as a standard antioxidant. In turn, carvacrol was characterized by the strongest effect against the examined strains of bacteria, both Gram-positive and Gram-negative. The chitosan film with carvacrol showed the most valuable antibacterial and mechanical properties (tensile strength and elongation at break). The antibacterial activities of the chitosan–carvacrol films were higher than that of the carvacrol solution. The inhibition zones of the chitosan–carvacrol films were in the range 29–41 mm (except for Enterococcus faecalis, with an inhibition zone of 15 mm) compared to the inhibition zones of the carvacrol solution (28 mm). The results showed that chitosan is an effective carrier of fragrance compounds, mainly carvacrol. However, all the tested chitosan-based films with the addition of fragrance compounds showed appropriate parameters (biological, mechanical, and barrier), which makes them an ecological alternative to plastics intended for food packaging.