Objective: To evaluate the effect of different cyclodextrins (β-cyclodextrin [β-CD], methyl-β-cyclodextrin [Mβ-CD], or hydroxypropyl-β-cyclodextrin [HPβ-CD]) and/or hydrophilic polymers (carboxymethylcellulose, hydroxypropylmethylcellulose [HPMC], polyethyleneglycol, or polyvinylpyrrolidone [PVP]) on daidzein solubility in water.
Materials and methods: The corresponding associations were characterized in aqueous media using phase-solubility studies. The morphology of daidzein/cyclodextrin freeze-dried complexes was characterized using scanning electron microscopy, and their spatial configuration was proposed by means of nuclear magnetic resonance spectroscopy.
Results and discussion: In the presence of 6 mM of cyclodextrins, the solubility of daidzein in water was significantly enhanced: 5.7-fold (β-CD), 7.2-fold (Mβ-CD), and 9.4-fold (HPβ-CD). The analysis of the three solid complexes proved that the formation of inclusion complexes occurred through the insertion of the B and C rings of daidzein molecule into the cyclodextrins cavity. The association of daidzein/cyclodextrin complexes to the hydrophilic polymers HPMC or PVP (1%, w/w) was able to improve the solubility of daidzein even further.
Conclusion: The highest solubilizing effect was obtained for daidzein/HPβ-CD/PVP ternary system (12.7-fold).