2-Hydroxypropyl-β-Cyclodextrin-Based Complexes Improve Polyphenol Solubility and Bioaccessibility: Evaluation by Validated HPLC–DAD Method

Propolis is a rich natural source of biologically active polyphenols; however, their therapeutic potential is often limited by poor oral bioaccessibility and bioavailability. This study reports the development and validation of a high-performance liquid chromatography-diode array detector (HPLC-DAD) method optimized for the quantification of major propolis polyphenols-caffeic acid (CA), pinocembrin (PC), chrysin (CR), caffeic acid phenethyl ester (CAPE), and galangin (GN) in 2-hydroxypropyl-β-cyclodextrin (HP-β-CD)-based complexes. A green complexation approach based on HP-β-CD and lyophilization was applied to continental propolis, yielding a water-soluble formulation suitable for oral administration. The isocratic HPLC-DAD method demonstrated linearity, sensitivity, and precision, suitable for reliable analysis of polyphneols in cyclodextrin-based matrices. Gastrointestinal behavior was evaluated using a simulated oral, gastric, and intestinal digestion model. PC and CAPE remained stable throughout digestion, whereas GN, CR, and CA showed higher sensitivity, with decreases of 43.1-71.6% compared to undigested samples. HP-β-CD complexation enhanced polyphenol solubility and improved gastrointestinal stability. Intestinal bioaccessibility, assessed by a centrifugation model, ranged from 77.2% (CR) to 124.9% (CA). However, the complexes did not permeate the artificial intestinal membrane, resulting in reduced dialyzable polyphenols, with CA being undetectable. These findings provide a validated analytical platform and mechanistic insight into the gastrointestinal behavior of cyclodextrin-complexed propolis polyphenols, supporting their application in oral functional formulations.