Hydrotropic and solvent strategies to enhance the solubilization of polyphenols in relation to their chemical structure

Abstract

Numerous natural polyphenols have a positive and beneficial effect on human’s health. However, they often have a poor solubility in water which limits their concentration of use and can reduce their bioavailability. Increasing their solubility could be thus of interest not only to boost their health properties but also for the preparation of concentrates that could be stored and diluted upon application. The solubility of the six natural polyphenols, quercetin, morin, naringenin, phloretin, trans-resveratrol and xanthohumol was studied. On one hand, the solubility of xanthohumol, quercetin, morin and naringenin was considered in water, when adding meglumine (for xanthohumol) or pyrogallol and phloroglucinol (for quercetin, morin, and naringenin, as potential hydrotropic solubilizers. It turned out that these additives considerably increased the polyphenols’ solubility in water. On the other hand, to understand the interactions between the different components in the aqueous solutions, the solubility of the polyphenols was also investigated in two ethanol-based binary mixtures with triacetin and cinnamaldehyde. These systems were modelled with COSMO-RS and experimentally investigated with UV–vis spectroscopy. The findings led to a better understanding of the relative importance of chemical structure, hydrogen bonds and π-stacking for solubilization. The different behaviors of the studied polyphenols regarding the methods and solvents used highlight the distinct factors hindering their water-solubility and thereby enable us to gain insight into potential strategies to better solubilize a given polyphenol in relation to its structure.