Cydonia oblonga Mill. Whole-Fruit Extract as a Multifunctional Cosmetic Ingredient: Biocompatibility and Concentration-Dependent Effects on the Rheological and Sensory Properties of O/W Emulsions

Background: Cydonia oblonga Mill. is a promising plant-derived ingredient for topical formulations due to its phytochemical composition and potential biological and technological properties. This study aimed to evaluate C. oblonga extract as a multifunctional cosmetic ingredient and investigate its concentration-dependent effects on the physicochemical, rheological, and sensory properties of oil-in-water (O/W) emulsions. Materials and Methods: Aqueous and 70% ethanolic extracts were prepared by maceration and reflux extraction and evaluated for phytochemical composition and antioxidant activity. The selected extract was assessed for in vitro biocompatibility and antibacterial activity and incorporated at increasing concentrations (1%, 3%, and 5%) into O/W emulsion creams prepared by a conventional hot emulsification method, involving separate heating of the oil and aqueous phases, followed by their combination under mechanical stirring and subsequent addition of the extract during cooling. The formulations were evaluated for pH, steady-shear, oscillatory and thixotropic rheological properties, and sensory characteristics. Results: Ethanolic reflux extraction yielded the highest total phenolic and flavonoid contents and the strongest DPPH radical-scavenging activity, with chlorogenic acid identified as the predominant phenolic compound. The extract maintained cell viability above 70% in HaCaT keratinocytes and MRC-5 fibroblasts and showed concentration-dependent antibacterial activity. Increasing extract concentration lowered formulation pH and increased structural strength and resistance to deformation, while all formulations retained shear-thinning behavior. Sensory evaluation revealed significant differences in thickness, stickiness, and spreadability. Conclusions: C. oblonga extract demonstrated favorable biocompatibility and multifunctional technological potential for the development of topical semisolid formulations.