The adenine-modified edible chitosan films containing choline chloride and citric acid mixture

A series of biopolymeric chitosan-based (Ch) films were prepared with choline chloride and citric acid plasticizer (deep eutectic solvent, DES). An effect of adenine (A, vitamin B4) addition on the functional properties of these films was evaluated. Several physicochemical and mechanical properties were tested: Fourier-transformed infrared spectra proved DES's plasticizing and crosslinking effect, while scanning electron microscopy and atomic force microscopy techniques confirmed the possible phase separation after adenine addition. These changes affected the mechanical characteristics and the water vapor and oxygen permeability. The prepared materials are not water soluble because the CA acts as a crosslinker. The adenine addition on antioxidative and antimicrobial properties was also checked. It was found that Ch-DES materials with A exhibit improved antioxidative properties (55.8-66.1% of H₂O₂ scavenging activity) in contrast to the pristine chitosan-DES material (51.1% of H₂O₂ scavenging activity), while the material is still non-mutagenic (lack of growth of Salmonella typhimurium) and possesses antimicrobial features (no E. coli observed for all the tested films and inhibition zones noted for S. aureus). The mentioned properties, reduced oxygen transmission (1.6-2.1 g m^-2 h^-1), and mechanical characteristics within the range of typical food packaging plastics proved the potential of Ch-DES-A films in the packaging sector. Moreover, the antioxidative properties, usage of substrates being allowed as food additives, and the presence of adenine create the advantage of the Ch-DES-A materials as edible coatings, being also a source of Vitamin B4.