Bio-Based materials for active food packaging Upcycling White Grape Pomace Extract into Chitosan-Based Films

In the last decade, the development of bio-based active films for food packaging has gained significant attention, driven by their potential to improve product shelf-life, reduce environmental impact, and promote sustainability. In this context, chitosan, a natural polysaccharide extracted from several natural sources, has been widely studied and applied as material in active packaging systems. Its main limitation is represented by the residuals of organic acids commonly used for wet processing. The present study investigates the valorization of white grape pomace, by-product of the winemaking process, 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 solid-liquid extraction using a 60% ethanol solution with a ratio of 1:8. The extraction was performed at 60 °C for 1 hour, and the resulting extract was subsequently purified using Amberlite XAD16N resin. The extract purification was performed to concentrate polyphenols while removing undesirable compounds such as sugars, amino acids, and waxes. The purified extract was then characterized before its incorporation into chitosan-based film. The extract presented a total polyphenol content of 111.8 ± 2.4 mg GAE/g determined by the Folin-Ciocalteu assay. Additionally, the bioactive characteristics of the extract were evaluated by focusing on antioxidant properties, performing DPPH, ABTS, and FRAP assays. The DPPH assay revealed an antioxidant capacity of 976 ± 37.22 μmol TE/g extract, while the ABTS assay showed a value of 570.54 ± 0.18 mg TE/g extract. Additionally, the FRAP assay indicated a notable increase in reducing power, with the purified extract reaching 5642.11 ± 161.62 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 (CO2). The carbonation process is reversible, thus facilitating the removal of acidic residues from films and coatings [1]. Acid-free chitosan films were then prepared by successfully adding the extract with a concentration in the range between 0-10% 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 had superior water stability, and barrier properties (Water Vapor Permeability = 0.013 ± 0.001 g mm m-2 d-1 Pa-1, Oxygen Permeability = 4.1 ± 0.4 cm3 μm m-2 d-1 Pa-1), compared to commonly acetic acid ones. The coatings were tested on model food matrices to assess their effectiveness as active edible packaging. ACKNOWLEDGMENT Project “ON Foods –Research and innovation network on food and nutrition Sustainability, Safety and Security – Working ON Foods”, funded under the National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 1.3 - Call for proposals No. 341 of 15 March 2022 of Italian Ministry of University and Research funded by the European Union – NextGenerationEU; Project code PE00000003, Concession Decree No. 1550 of 11 October 2022. REFERENCES [1] Casalini R., Ghisoni F., Bonetti L., Fiorati A., De Nardo L., 2024. “Development of acid-free chitosan films in food coating applications: Provolone cheese as a case study”, Carbohydrate Polymers, 331, 121842, 10.1016/j.carbpol.2024.121842.