Valorization of spent coffee ground through the development of alginate-based composite antioxidant films: Physicochemical properties and release kinetics

The study aimed to valorize the oily extract of spent coffee ground (SCG-O) by developing an antioxidant-active biopolymeric film and investigating how the film structure affected its properties. Two film systems were studied: alginate at 2 % (SA) and polyelectrolyte complex of SA and chitosan (CH) (1.5:0.5), both prepared with and without the inclusion of SCG-O at 0.6 %. The film-forming solutions (FFSs) were evaluated for apparent viscosity, ζ- potential, particle size distribution (PSD), and Turbiscan stability index (TSI). The films were characterized by FT-IR and assessed for solubility, water vapor sorption, water vapor permeability. The release of selected antioxidant compounds (ACs) - caffeine, chlorogenic acid, caffeic acid, 3,4 dihydroxybenzoic acid, and ferulic acid- from the active film into a food simulant (50 % ethanol), was assessed at 4 °C and 20 °C, along with antioxidant activity using the DPPH assay. The inclusion of SCG-O increased the viscosity and ζ-potential (from -70 mV to -56 mV) of SA films. However, both FFS showed similar PSD (60–170 nm) and TSI values (1–3). FT-IR analysis indicated strong interactions between the components, particularly through hydrogen bonding and interactions between carboxylate and amine groups. SCG-O reduced water solubility and water sorption but did not affect water vapor permeability. The release rate of ACs varied based on film composition, with the SA+CH blend showing higher antioxidant capacity, suggesting lower encapsulation efficiency than SA film.