Multifunctional chitosan/tannic acid composite films with improved anti-UV, antioxidant, and antimicrobial properties for active food packaging

Chitosan (CS) has been extensively studied because of its biocompatibility, biodegradability, low toxicity, and good film-forming properties. However, pristine CS has relatively low UV resistance, antioxidant, and antibac-terial properties, and is thus not suitable for food packaging. In this study, multifunctional tannic acid (TA) was incorporated into pristine CS to overcome its limitations. Two neutralization conditions with different pH (pH 7.4 using phosphate-buffered saline (PBS) and pH 8.5 using Tris buffer) were employed to prepare CS-TA composite films. The chemical and structural characteristics of the composite films were analyzed through Fourier-transform infrared, UV-visible, and X-ray photoelectron spectroscopies. At the higher neutralization pH of 8.5, the covalent crosslinking between CS and TA increased because more TA was transformed into quinone form. In addition, the Schiff base reaction was predominant when neutralized with PBS (pH 7.4), whereas the Michael addition reaction was predominant when neutralized with Tris buffer (pH 8.5). The CS-TA composite films exhibited better mechanical, thermal, antioxidant, and antibacterial properties than those of pristine CS. Furthermore, the packaging film of the composite effectively reduced enzymatic browning and water loss from bananas. The findings suggest that the CS-TA composite films can be used as active packaging materials for long-term food storage owing to their excellent mechanical, antioxidant, and antibacterial properties.