Effect of process conditions on the stability and physicochemical properties of green coffee oil Pickering emulsions stabilized with ZnO nanoparticles for quercetin-enhanced sunscreen formulations

Solar ultraviolet (UV) radiation is the primary etiological factor in the development of several cutaneous malignancies, including carcinomas. In this context, the use of sunscreen formulations usually helps to prevent and reduce UV skin damage. The aim of this work was to explore the impact of the process conditions on some relevant physicochemical properties in sunscreens with a formulation based on quercetin Pickering emulsions stabilized with ZnO particles. Four formulations were prepared by controlling the speed and homogenization time using green coffee oil as the external phase and a mixture of stabilizers, water, and polyethylene glycol as the dissolution media. The stability of the emulsified systems was analyzed in terms of time after 28 days of storage by optical microscopy and digital image analysis to determine the mean particle size. The Turbiscan Stability Index (TSI), Sun Protection Factor (SPF), rheological behavior, and antioxidant activity were also evaluated. The system with the highest physical stability, minimal changes in rheological properties, and superior stability during storage time with respect to breakage phenomena was obtained at 15,000 rpm/2 min, with a SPF of ~ 40 and exhibiting one of the highest antioxidant capacities compared to other treatments. This stability was constant during the evaluation period. With these results we established the optimal conditions for the potential development of sunscreens with desirable attributes to reduce the harmful effects of UV radiation in addition to establishing the encapsulation conditions of bioactive compounds and facilitating its scale-up.