Human exposure and stability of a novel Citrus flavanone-based nutraceutical: a multi-matrix analytical approach

Introduction: Citrus flavanone glycosides are widely investigated for their potential health benefits, including antioxidant, anti-inflammatory, and cardiometabolic effects; however, human exposure and metabolic fate are often inferred from plasma measurements alone, despite limited systemic absorption and extensive intestinal processing. Methods: In this study, we performed an integrated, translational assessment of human exposure to a novel Citrus flavanone-based nutraceutical formulation (FlavonAid™), combining plasma, urinary, and fecal analyses with comprehensive analytical characterization and stability evaluation. Six healthy volunteers received a single oral dose (174 mg total flavanones), and flavanone-related compounds were quantified in plasma, urine, and feces using validated chromatographic methods. Results: Accelerated stability testing demonstrated minimal degradation (<3.5% over 6 months) and high reliability of the formulation. Plasma analysis revealed low and intermittent systemic exposure, with concentrations frequently close to analytical limits and no reproducible pharmacokinetic profiles. In contrast, urinary and fecal analyses showed substantial recovery of flavanone-related compounds within 24 h. Mass balance analysis indicated that approximately 39% of the administered dose was recovered in urine and feces during the first 24 h, mainly as hydrolyzed parent flavanone glycoside equivalents, while shared low-molecular-weight phenolic metabolites accounted for a major fraction of the excreted material. Discussion: Overall, these findings demonstrate that human exposure to Citrus flavanones is best described through a multi-matrix approach that captures coordinated intestinal metabolism, partial systemic handling, and prolonged elimination rather than relying solely on plasma data. This study establishes a robust methodological framework for evaluating flavanone-based nutraceuticals in humans and supports further investigation of formulations designed to achieve sustained intestinal exposure with limited systemic availability.