Sustainable chitosan packaging films: Green tea polyphenolic extraction strategies using deep eutectic solvents

In this work, an alternative approach towards the use of a ternary natural deep eutectic solvent (ChCl/glycerol/ lactic acid: NADES-3) as an environmentally friendly medium for the extraction of polyphenolic compounds from green tea (GT) was investigated. The ternary NADES have a higher capacity of polyphenolic extraction in comparison with the other two binary NADES (NADES-1 and NADES-2, ChCl/glycerol and ChCl/Lactic acid, respectively). The extraction GT solutions were used to improve chitosan (Chit) film properties, using the casting method, to produce films with and without different GT/NADES (ternary and binary) plasticizers. Transparent, uniform, and homogeny films (without cracks or pores) were obtained and evaluated in terms of mechanical, water resistance, optical and microstructural properties. The results were compared with those obtained for chitosan films containing binary deep eutectic solvents (ChCl/glycerol and ChCl/lactic acid, with and without GT)) as plasticizers in their formulations. In this sense, the presence of GT polyphenolic compounds led to different surface structures, and the surface of the biofilms become rougher with the increase of GT content. FTIR spectra confirmed physical entanglements film components and suggested the existence of the interaction between the extract's polyphenols and the Chit matrix. Films with 10% of NADES (binary and ternary) showed good high water barrier properties. Regarding mechanical properties, they also showed higher resistance, being the NADES-2 (10%) the film with better resistance.

Automated summary

This study investigates the use of a ternary natural deep eutectic solvent for the extraction of polyphenolic compounds from green tea. The extracted solutions are then used to improve the properties of chitosan films, and the resulting films are evaluated for mechanical, water resistance, optical, and microstructural properties. The presence of GT polyphenolic compounds leads to different surface structures, and films with 10% of NADES show good high water barrier properties and higher resistance.