Effects of capsaicin loads on the properties of capsicum leaf protein-based nanocellulose composite films

This study aims to enhance the functionality of conventional protein-based nanocellulose composite films (PNCF) to meet the high demand for natural antimicrobial packaging films. Capsicum leaf protein (CLP) and cellulose nanocrystals (CNCs) extracted from capsicum leaves were used as raw materials. Capsaicin, an essential antibacterial active ingredient in the capsicum plant, was used as an additive. The influence of different capsaicin loads on PNCF physicochemical and material properties was investigated under alkaline conditions. The results show that all film-forming liquids (FFLs) are non-Newtonian fluids with shear thinning behavior. When the capsaicin loading exceeds 20 %, the surface microstructure of PNCF changes from dense lamellar to rod-like. Capsaicin did not alter the PNCF crystal structure, thermal stability or chemical bonding. Capsaicin can be loaded onto the PNCF surface by intermolecular hydrogen bonding reactions with CLP and CNC, preserving capsaicin's biological activity. With increasing capsaicin loads from 0 % to 50 %, the mechanical and hydrophobic properties of PNCF decreased, whereas the diameter of the inhibition zone increased. All PNCFs have UV-blocking properties with potential applications in developing biodegradable food packaging materials. The results of this study provide a theoretical basis for the high-value utilization of capsicum cultivation waste and the preparation of novel PNCF.