Sustainable food packaging films by methylcellulose enriched with spent coffee grounds extract

In this study, a sustainable strategy was developed to valorise spent coffee grounds through water-based extraction of functional molecules, which were incorporated into methylcellulose (MC) to fabricate biodegradable composite films for food packaging applications. The effects of the spent coffee grounds extract (SCGe, 2.5-10 wt%) on the thermal, optical, wettability, and mechanical properties, as well as functional performances, were systematically investigated. SCGe addition conferred strong UV-shielding capability, dramatically increasing the UV protection factor (UPF) from 1.4 for neat MC to 360 for films with 10 wt% SCGe. Importantly, the composite films retained their UV-blocking efficiency after 30 days of UV irradiation. Prolonged UV exposure also increased tensile strength and elastic modulus, suggesting that UV-induced cross-linking is mediated by coffee-derived bioactive compounds. Antioxidant performance increased with SCGe content, reaching almost complete (∼100%) DPPH radical scavenging at SCGe loadings ≥5 wt%. The applicability of the films was assessed through strawberry preservation tests. Fruits coated with MC/SCGe formulations showed significantly reduced mass loss (from 12.1 wt% up to 24.1 wt%), limited colour variation, and mechanical resistance comparable to fresh strawberries, as confirmed by gravimetric, colorimetric, and compression analyses. Overall, the results highlight that spent coffee grounds extract is a highly effective, multifunctional additive for producing bio-based films with enhanced UV stability, antioxidant activity, and food-preservation performance.