Thermodynamic and Structural Evaluation of the Icariside II and Whey Protein Concentrate Complexes

Icariside II (ICS), the main active component of the Herba Epimedii, has attracted abundant interest due to its extensive range of potential health-promoting applications such as cancer prevention, treatment of cardiovascular disease, osteoporosis and erectile dysfunction and delaying the effects of Alzheimer’s disease. However, its great potential as a food supplement is diminished by its poor bioavailability. Although in the case of other flavonoids complexation with whey protein concentrate (WPC) resulted in significant bioavailability improvement, so far, no studies investigated the complex formation with icariside II. This study focuses on understanding the interactions between icariside II and WPC, with a specific focus on β-lactoglobulin (β-lg), its main protein component. The comparison of the performed X-ray powder diffraction, differential scanning calorimetry and Fourier transform infrared spectroscopy measurements between the raw mixture of WPC and ICS and the complex provides evidence of the formation of a new supramolecular ICS-WPC complex. The binding constant, binding number and thermodynamic parameters of the reaction were obtained using fluorescence spectroscopy. Additionally, a molecular docking study was performed to further investigate the interaction between ICS and β-lg. The complex formation of ICS-WPC opens up a new possibility to improve the bioavailability of the icariside II, thus contributing to the prevention and curing of many diseases.