Sustainable chitosan films containing a betaine-based deep eutectic solvent and lignin: Physicochemical, antioxidant, and antimicrobial properties

Biodegradable chitosan films are highly desirable for use as food packaging, but the poor mechanical properties, water sensitivity, and functional limitations of these films must be addressed. In this study, a new chitosan film was prepared from chitosan–citric acid/chitosan–adipic acid (CA) and chitosan–malic acid/chitosan–adipic acid (MA) solutions and plasticized by the incorporation of a natural betaine-based deep eutectic solvent (DES; 0–30 wt%) and lignin (1 wt%). The resultant films were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy, and X-ray diffractometry to evaluate the changes in the structural, physical, antioxidant, and antimicrobial properties. Analysis revealed that the films contain numerous particles in cross-section and have rough surfaces. Furthermore, the addition of 30 wt% DES with lignin resulted in a significant increase in the elasticity, water contact angle, and radical scavenging rate. Moreover, the presence of lignin in the films reduced the water vapor permeability because of its hydrophobicity. Additionally, the CA film containing lignin displayed good antibacterial activity against Staphylococcus aureus and Escherichia coli. Overall, the CA-based composite films demonstrated excellent potential for use as bioactive food packaging application.