Development, Stability and Bioactive Properties of a Novel Natural Nanoemulsion containing Cashew Residue Extract

: The growing interest in natural and sustainable products has driven research into phenolic bioactive compounds, which are known for their antioxidant properties. Cashew residue extract emerges as a promising source of these compounds, with the potential to add value to agro-industrial by-products. This study aimed to develop and evaluate a nanoemulsion containing cashew residue extract, emphasizing its antioxidant activity and applications in pharmaceutical, cosmetic, and food products. The methodology included enzyme-assisted extraction, characterization of the extract for total phenolic content (Folin-Ciocalteu method) and HPLC, evaluation of antioxidant activities (DPPH, ABTS, hydroxyl radical, reducing power, and TAC), anti-inflammatory activity (nitric oxide reduction), cytotoxicity, cell migration, and proliferation. Subsequently, the nanoemulsion was prepared, with formulation optimization and 90-day stability monitoring under different conditions, analyzing droplet size, PDI, zeta potential, pH, conductivity, and in vitro antioxidant activity. Results showed high phenolic content in cashew residue extract (327 ± 2.99 μg/L GAE, higher than reported in the literature), identification of eight compounds by HPLC (with quantification of gallic acid, p-coumaric acid, ferulic acid, and quercetin), strong antioxidant activity (ABTS 93.16% ± 0.53%, DPPH 68.78% ± 2.55%, hydroxyl 95% ± 0.09%, reducing power 96.47% ± 0.09%, and TAC 5.20 ± 0.01 mg/g), low cytotoxicity (>80% cell viability), significant NO reduction at 50 and 100 μg/mL concentrations, and stimulation of cell migration/proliferation. The nanoemulsion exhibited excellent physicochemical stability for 90 days (especially under refrigeration), 95.9% ± 0.34% encapsulation efficiency, and superior performance compared to the pure extract in vitro antioxidant and anti-inflammatory activities. It is concluded that the cashew residue extract nanoemulsion shows promising potential as a candidate for innovative and sustainable cosmeceutical applications. Although ex vivo safety screening (HET-CAM) has been performed, future clinical trials in human volunteers are required to confirm its dermatological efficacy and safety in finished cosmetic products.