Biomimetic asymmetric films for simultaneous active preservation and colorimetric freshness monitoring of protein-rich foods.

Inspired by lotus-leaf asymmetric wettability, we developed a dual-functional asymmetric film for intelligent food packaging. The hydrophilic inner layer (polyvinyl alcohol/lignocellulose nanofibrils/quercetin) provides active preservation and sensing, while a hydrophobic outer layer with lotus-leaf micro/nano-topography and carnauba wax coating acts as a moisture barrier. Lignin in the nanofibrils forms hydrogen bonds and π-π interactions, enhancing mechanical strength, UV-blocking (>95% at 400 nm), and antioxidant capacity (>80% 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging). The film also inhibits E. coli and S. aureus. Quercetin undergoes reversible deprotonation at alkaline pH (8-12), producing a distinct yellow-to-orange color change that aligns with protein-rich food spoilage. During shrimp monitoring, chromatic values correlated linearly with spoilage (R2 = 0.989). For pork, the packaging extended refrigerated shelf life by 2 days, delaying pH rise and reducing drip loss. This biomimetic design offers a scalable, green strategy for active intelligent food packaging.