Valorization of grape pomace through alginate-pectin beads cross-linked with Ca2+ and Fe3+ for the stabilization and delivery of antioxidant polyphenols

Grape pomace (GP), a winemaking by-product, is rich in polyphenols with antioxidant activity, but is prone to degradation. In this study, ethanolic extracts of GP were encapsulated in polysaccharide-based beads to enhance stability and enable controlled release. Alginate, low-methoxyl pectin, and an 80/20 pectin-alginate blend were cross-linked with Ca2+ or Fe2+ at two concentrations (4% and 8% w/v) to systematically adjust the network structure and release behavior. All formulations achieved high loading efficiencies (87-95%), but release and antioxidant performance were strongly matrix-dependent. The Pectin-Ca2+ beads, which contained 75% GP extract (formulation T), showed the highest efficacy, reducing intracellular ROS in HaCaT cells by up to 78%. Thermal analysis suggested that Fe2+ crosslinking enhanced solid-state stability through polymer-ion and metal-polyphenol interactions. These results demonstrate that tuning polysaccharide composition and crosslinking chemistry allows simultaneous control of polyphenol release and stabilization, providing a rational design framework for GP-based functional ingredients.