From spent coffee residues to sustainable packaging: Zein-based active films produced via supercritical impregnation

The reuse of residues from the agri-food industry for the development of active food packaging represents a sustainable alternative that has gained increasing attention in recent years. In this work, active zein films were produced by impregnating them with a multicomponent extract derived from spent coffee grounds – a rich natural source of antioxidants, polyphenols, and other bioactive components – via a sustainable supercritical carbon dioxide technique. This process offers a novel and eco-friendly approach to loading bioactive multicomponent extracts onto biodegradable films. The extracts were obtained via high-pressure and temperature extraction (HPTE), while the zein films were produced using either solvent casting (ZCAS) or electrospinning (ZELC). Supercritical impregnation was employed to load a multicomponent extract into zein films. Process parameters such as temperature and contact time were optimized to maximize impregnation efficiency. The loading, quantified using caffeine as a reference compound, was 0.64 mg caffeine/g film for ZCAS and 0.93 mg caffeine/g film for ZELC. The impregnated zein films exhibited enhanced light barrier properties and antioxidant activity, as confirmed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) analysis, indicating their potential as sustainable, active, and eco-friendly packaging materials. Moreover, the use of spent coffee grounds as a source of active ingredients, combined with zein as the film matrix, provides a novel upcycling strategy. This dual-function approach aligns with current efforts to enhance food system sustainability through innovations in material science and waste valorisation. • Active zein films prepared using extracts from spent coffee grounds. • Use of supercritical CO₂ to load multicomponent extracts into films. • Comparison of films made by solvent casting (ZCAS) and electrospinning (ZELC). • Loading of 0.64 mg/g ZCAS and 0.93 mg/g ZELC using caffeine as active compound. • Impregnated films showed enhanced antioxidant and light barrier properties.