Upcycled White Grape Pomace for Chitosan-Based Active Food Packaging

The present study investigates the valorization of white grape pomace to recover bioactive extracts for incorporation into chitosan-based films obtained through a novel acid-free procedure. Initially, the white grape pomace was subjected to conventional extraction using a 60% ethanol solution at 60 °C for 1 hour, then purified using Amberlite XAD16N resin. The extract presented a total polyphenol content of 111 ± 2 mg GAE/g. Additionally, the DPPH assay revealed an antioxidant capacity of 976 ± 37 μmol TE/g extract, while the ABTS assay showed a value of 570.5 ± 0.2 mg TE/g extract. Additionally, the FRAP assay indicated a notable increase in reducing power, with the purified extract reaching 5642 ± 161 μmol Fe(II)/g extract. Chitosan solutions were prepared by means of an initial dissolution of chitosan in aqueous organic acid, subsequent neutralization, and a resulting gel dissolution in water by introducing carbon dioxide. The carbonation process is reversible, thus facilitating the removal of acidic residues from films and coatings. Acid-free chitosan films were then prepared by incorporating the extract at concentrations from 0 to 10% w/wChitosan. Chitosan solutions’ rheological and films’ properties (water stability, barrier, and optical properties) were characterized. The shear thinning behavior of the chitosan solution showed a suitable viscosity for the coating process (viscosity in the range 104-103 cP for shear rate 10-100 s-1). Acid-free chitosan films presented a Water Vapor Permeability of 0.013 ± 0.001 g mm m-2 d-1 Pa-1 and an Oxygen Permeability of 4.1 ± 0.4 cm3 μm m-2 d-1 Pa-1. The materials were tested on model food matrices to assess their effectiveness as active edible packaging.