Chitosan films tailored with deep eutectic solvent extracts from Hibiscus sabdariffa: Fabrication and characterization

Natural polymers are the most promising alternatives to petroleum-based plastics for developing biodegradable food packaging films. However, the brittleness and lack of active protection of films from most natural polymers pose a challenge to their practical application. The addition of plasticizers and natural extracts to these films is considered an effective solution to address these issues. In this study, the potential for the use of deep eutectic solvents (DESs) and DES extracts derived from Hibiscus sabdariffa in the production of chitosan films and their effects on their mechanical and antioxidant properties were examined. Initially, the extraction efficacy of DESs composed of choline chloride (ChCl) and various carboxylic acids (citric, lactic, tartaric, and oxalic acids) was evaluated in terms of phenolic and anthocyanin contents along with antioxidant activities. Optimal results were achieved with the utilization of ChCl-oxalic acid as the extraction medium. Subsequently, chitosan films were fabricated by introducing DESs and DES extracts as plasticizers and compared with glycerol-plasticized chitosan films. The incorporation of DESs and DES extracts into the film matrix led to a notable reduction (11.78–14.82%) in moisture content compared with glycerol (25.34%). Notably, using ChCl-tartaric acid improved the tensile strength, while ChCl-citric acid enhanced the film flexibility. Films containing ChCl-tartaric acid demonstrated exceptional light barrier properties. SEM analysis revealed an interaction between chitosan and DESs, which was further corroborated by FTIR and XRD. Additionally, DES extracts provided superior antioxidant activity to the films than their pure DESs. These findings suggest a significant potential for DES extracts from Hibiscus sabdariffa as bioactive agents and plasticizers in chitosan films.