Fabrication of a Chitosan–Gelatin/Polylactic Acid Bilayer Active Film Loaded with Tannic Acid for Enhancing Shelf-Life of Refrigerated Baby Clams

Active bilayer (BL) packaging films were developed by depositing chitosan/fish gelatin blend containing tannic acid (TA) at varying levels (1, 3, and 5%; w/w) onto a polylactic acid layer. Augmenting TA levels enhanced strength (17.27 MPa to 27.57 MPa) but reduced flexibility (85.03% to ~38%) due to enhanced polymer cross-linking induced by TA, as confirmed by FTIR. The films exhibited exceptional UV-blocking capabilities, in which UVB protection reached 98.34% and 100% for films with 1% and 3% TA, respectively. SEM micrographs revealed uniform dispersion of TA with defect-free matrices. The antioxidant activity of the films upsurged with rising TA levels. When baby clam edible portions (BC-EP) were packed in pouches made with BL films, the pouches containing 5% TA most effectively slowed lipid oxidation and inhibited spoilage during 12 days of refrigerated storage. Total viable count, psychrotrophic bacteria count, and counts of specific spoilage organisms were decreased. Reductions in spoilage bacteria including Shewanella and Pseudomonas and dominance of lactic acid bacteria were confirmed using next-generation sequencing analysis. The release kinetics of TA followed Fickian diffusion, enabling sustained antioxidant and antimicrobial action. TA-containing pouches therefore effectively extended the shelf life of BC-EP through synergistic barrier, antioxidant, and antimicrobial mechanisms, offering a sustainable alternative to conventional plastic packaging.