Natamycin-loaded hydroxypropyl CS-lignin/gelatin/ZnO films for photoresponsive antibacterial activity and sweet potato preservation

HPCS-stabilized lignin nanoparticles enhanced natamycin solubility and stability. • Gelatin/ZnO films incorporated with LNPs showed superior mechanical and barrier properties. • Films exhibited synergistic photothermal and ROS-mediated antibacterial activity. • Lignin shielded natamycin from degradation, balancing stability and antibacterial efficacy. • Coating extended sweet potato shelf life and showed favorable biodegradability. To address the poor photostability and low aqueous solubility of natamycin (N), a hydroxypropyl chitosan (HPCS)-stabilized lignin nanoparticle (LNP) delivery system (LNP-N/HPCS) was developed in this study. The results showed that the nanocarriers exhibited a high encapsulation efficiency (89.17 ± 2.8%) and a moderate loading efficiency (11.63 ± 0.1%), while significantly increasing the solubility of natamycin to 13.5 times that of its free form at room temperature. Structural analysis indicated that LNP-N/HPCS formed stable core–shell-like nanostructures through hydrogen bonding, van der Waals forces, and π–π interactions, enabling efficient loading and stable dispersion. Furthermore, the delivery system was incorporated into gelatin/ZnO composite films (Gel/ZnO/LNPs) to construct multifunctional active packaging materials. The resulting composite film exhibited good antioxidant activity, mechanical properties, and gas barrier properties. After 10 min of xenon lamp irradiation, the composite film rapidly heated to 54.6 °C. After 150 min of irradiation, 67.55% of the initial natamycin content remained in the Gel/ZnO/LNPs5 composite film, whereas the retention rate of free natamycin was only 24.72%, indicating that the LNP delivery system improved the photostability of natamycin. In addition, the composite system exhibited good antibacterial activity in both film-forming solutions and solid films. In particular, Gel/ZnO/LNPs5 exhibited nearly complete growth inhibition against Escherichia coli , Staphylococcus aureus , and Dickeya dadantii E36 after 10 min of light irradiation, and achieved an inhibition rate of approximately 85% against Fusarium solani-melongenae 24–3. After 150 min of continuous irradiation, the Gel/ZnO/LNPs5 film still exhibited an inhibition rate of 55.67% against Fusarium solani-melongenae 24–3. Practical application results showed that the composite film could delay quality deterioration of sweet potatoes during storage to some extent and gradually disintegrated within approximately 6 days in soil. In addition, no significant inhibitory effect was observed in the seed germination test. Overall, this study provides an effective strategy for developing multifunctional food packaging materials with photothermal responsiveness, light-enhanced antimicrobial activity, and postharvest preservation functions. Download: Download high-res image (225KB) Download: Download full-size image