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.