Curcumin-loaded O/W Pickering emulsion stabilized by (Ligno)cellulose nanofibers: impact of surface charge, morphology, and chemical composition on emulsion efficacy, storage stability and bioaccessibility

Abstract

The bioaccessibility of lipophilic bioactive compounds, such as curcumin, is commonly limited by their lipophilic nature, which decreases their solubility in the gastrointestinal system. This study presents the formulation of hydrocolloid-based Pickering emulsions (PEs) stabilized by plant-derived cellulose and lignocellulose nanofibers (CNFs and LCNFs) to protect curcumin throughout its shelf life in the food chain, from storage to dietary intake. An in-depth characterization of these delivery systems correlated nanofiber physicochemical characteristics with the emulsifying capacity, droplet size distribution, physical stability, rheology, microstructure, encapsulation efficiency, photoprotection and bioaccessibility. Chemically pretreated nanofibers (CNF-TO and LCNF-TO) showed superior emulsifying capacity compared to mechanically pretreated ones, achieving long-term emulsion stability (creaming index < 1%) at concentrations as low as 0.25% w/w, attributed to their higher surface charge (up to −35.8 mV) and specific surface area. CNF-TO or LCNF-TO-stabilized curcumin PEs maintained a creaming index < 10% for two months. CNF-TO-stabilized curcumin PEs showed the smallest droplet sizes (< 5 µm). Curcumin addition reduced droplet size, improving emulsion stability, with CNF-TO demonstrating superior structuring ability due to its smaller fiber diameter and higher specific surface area. Rheological analysis showed that CNF-TO-stabilized PEs exhibited the highest viscosity (k = 11.69 Pa·sn), attributed to a more robust network structure. Curcumin encapsulation efficiencies were ≥ 95%, with minimal degradation under visible light. Microencapsulation of curcumin significantly improved its bioaccessibility, from < 10% to 22.3% (LCNF-TO) and 45.5% (CNF-TO), identifying CNF-TO as the most effective stabilizer.