Improving solubility and stability of fat-soluble vitamins (A, D, E, and K) using large-ring cycloamylose

Fat-soluble vitamins (FSV) have beneficial biological activities, but their application is limited due to low solubility and stability. We investigated the capability of cycloamylose (CA) to improve the solubility and stability of FSV by forming a complex. The PXRD, FTIR, fluorescence spectrometry, 1D NMR, and 2D NMR analyses supported the complex formation between CA and FSV in both solution and solid states. Especially, interaction between FSV hydrophobic moiety and CA interior was elucidated by NMR. The solubility of FSV continuously increased without aggregation in 5% ethanol solution at 30 °C with CA concentration of up to 60 mM, while it either reached to plateau or showed a maximum value with the concentration of cyclodextrin (CD) and maltodextrin (MD), commercial agents. As CA concentration increased, a photo-degradation rate of FSV significantly reduced in 5% ethanol solution at room temperature (RT). Highly soluble and stable characteristics of CA, especially at high concentration, were responsible for the enhanced solubility and stability of FSV upon complexation with CA, suggesting the potential usage of CA as a promising host molecule.