Nanostructured Lipid Carriers for the Delivery of Curcumin and Quercetin from Nigerian Turmeric and Onion in Functional Foods

Curcumin from turmeric (Curcuma longa) and quercetin from onion (Allium cepa) are potent bioactive phytochemicals with documented anti-inflammatory, antioxidant, and chemopreventive properties, yet their poor water solubility and low oral bioavailability severely limit their functional food applications. This study develops nanostructured lipid carriers for the co-encapsulation and delivery of curcumin and quercetin extracted from turmeric cultivated in Edo State and onion from Kebbi State, Nigeria, and evaluates their application in functional yoghurt. The theoretical contribution is a bioaccessibility prediction model that relates nanocarrier physicochemical properties including particle size, polydispersity, and lipid composition to in vitro oral bioaccessibility using an in vitro digestion model calibrated to Nigerian dietary patterns. Nanostructured lipid carriers were prepared by hot homogenisation-ultrasonication using combinations of shea butter (solid lipid) and red palm oil (liquid lipid) as the lipid matrix. Particle characterisation was conducted by dynamic light scattering, transmission electron microscopy, and differential scanning calorimetry. Encapsulation efficiency, controlled release profiles under simulated gastrointestinal conditions, and bioaccessibility were determined. The nanocarriers were incorporated into yoghurt at a fortification level providing 15 mg curcumin and 10 mg quercetin per serving. Stability over 28 days of refrigerated storage and sensory acceptability were evaluated. Results showed encapsulation efficiency above 90 percent for both bioactives, with significant improvement in bioaccessibility to 42 percent for curcumin compared to 8 percent for free curcumin. The study contributes an original bioaccessibility model and nanocarrier design framework for African functional food applications. Keywords: nanostructured lipid carriers, curcumin, quercetin, bioaccessibility, functional food