Cellulose-based pickering emulsion films incorporating oregano essential Oil: Valorization of spent coffee grounds for active food packaging

This study aimed to develop biodegradable films from cellulose-based Pickering emulsions using milled and pulped spent coffee grounds (SCG) as a sustainable source of stabilizing particles. Cellulosic materials were extracted from SCG through ethanol pretreatment and peracetic acid (PAA) pulping, followed by particle size reduction using planetary ball milling. Emulsions were formulated with oregano essential oil (OEO), oleic acid (OA), and glycerol (GLY) in six different OEO/OA/GLY ratios and cast into films. The control emulsion (without OEO) exhibited the highest creaming index (CI) throughout 28 days of storage, while CI decreased as OEO concentration increased, indicating enhanced emulsion stability. No significant differences (p > 0.05) were found in film thickness (0.076–0.116 mm), tensile strength (1.60–2.58 MPa), elongation at break (3.43–5.41 %), or water vapor permeability (24.47–37.58 g mm/m²·d·kPa) across all formulations. The control film showed significantly higher transparency (11.93 %) and lower opacity (7.01 %) than OEO-containing films, with the 0.75OEO/0.25OA/0.25 GLY formulation exhibiting the lowest transparency (0.10 %) and highest opacity (26.63 %). Antioxidant activity increased with OEO concentration; the 0.75OEO/0.25OA/0.35 GLY film exhibited 73.81 % DPPH scavenging after 6 h, compared to only 11.72 % in the control. OEO-containing films inhibited Listeria innocua after 48 h but showed no effect against Escherichia coli. The thermal analysis revealed that OEO improved film flexibility and thermal stability. These findings demonstrate the potential of upcycled SCG-derived cellulose and OEO emulsions to produce functional, biodegradable films suitable for active food packaging applications.