Janus-architected gelatin-dialdehyde starch/zein bilayer films with strong antioxidant/UV-blocking performance and selective antibacterial activity for active food packaging.

The development of biodegradable packaging materials has gained increasing attention as alternatives to petroleum-based plastics. However, current bio-based packaging materials are based on a homogeneous structural design, which limits their effectiveness in inhibiting food spoilage caused by multiple factors, including microbial metabolism, oxidation reactions, and ultraviolet radiation. This study developed a Janus bilayer edible film utilizing gelatin and zein as substrates through layer-by-layer assembly technology, based on the Schiff base reaction and enzyme-catalyzed cross-linking. This approach achieved the co-loading of hydrophilic polylysine and hydrophobic curcumin, thereby endowing the bilayer film with antibacterial and antioxidant capabilities. Subsequently, the physicochemical properties, ultraviolet resistance, antibacterial activity, antioxidant activity, and fruit preservation ability of the Gelatin-Dialdehyde Starch-Polylysine/Zein-TGase-Curcumin (GDP/ZTC) films were investigated. The experimental results indicate that the GDP/ZTC film exhibits outstanding UV resistance, achieving a 100% UV blocking rate. It also demonstrates significant antioxidant activity, with DPPH and ABTS radical scavenging rate of 94% ± 0.09%, 87.08% ± 0.85%, respectively. The GDP/ZTC film inhibited S. aureus (65.35% ± 0.6%) and moderately inhibited E. coli (21.53% ± 1.22%), showing a Gram-positive-biased antibacterial effect. Moreover, the GDP/ZTC film performed excellently in blueberry preservation experiments, effectively maintaining the appearance, weight (with a weight loss rate of only 4.45% ± 0.51%), hardness (with a decrease of only 0.56 N), and anthocyanin content of blueberries even after 8 days. Overall, the Janus bilayer combines outstanding antioxidant/UV-barrier performance with selective Gram-positive-biased antibacterial function; moderate E. coli inhibition reflects a structure-function trade-off, highlighting sustainable food-packaging potential.