Chitosan-Deep Eutectic Solvent-Polyphenol Films

The deep eutectic solvent (DES) was prepared by mixing the ChCl powder (hydrogen bond acceptor) with Gly (hydrogen bond donor) at the molar ratio of 1:2 (w/w) [70 (link)], under constant magnetic stirring at 80 °C to obtain a homogenous mixture. The DES mixture was left to cool down and stored at room temperature until further analysis.
To film preparation, CS powder at 2.5% (w/v) was dissolved in a 1% (v/v) acetic acid solution under constant magnetic stirring overnight at room temperature. Later, the DES solution was added at 0 and 5% (v/v), as listed in Table 1, and then stirred overnight at 25 °C until full homogenization. The optimized açaí PECs (8:2 chitosan: sodium alginate PECs incorporated with 0.5% of açaí oil and cross-linked with 0.5% of CaCl₂) were prepared according to our previous work [39 (link)] and incorporated at different concentrations from 0 to 10% (v/v) into the CS-DES solution to obtain the film-forming mixture.
The film-forming solutions were cast in Petri dishes and dried in an oven at 60 °C for 24 h, followed by drying at room temperature in a desiccator under vacuum containing a modified atmosphere of anhydrous calcium chloride, ~25% of relative humidity (RH), until constant weight (~5 days), which resulted in the formation of thin CS-DES-PECs films (Scheme 1). The thickness of the films was controlled by casting the same weight (~15 g) of film-forming solutions in each plate. Finally, the films were stripped off from the glass plates, stored at room temperature and modified atmosphere (~25% of RH) until further analysis.