Influence of amphiphilic structures on the stability of polyphenols with different hydrophobicity

Autooxidation of five polyphenols representing range of different hydrophobicities (catechin gallate (CG), (-) catechin((-)C), epicatechin (EC), epigallocatechin gallate (EGCG) and epigallocatechin (EGC)) in three different aqueous solutions: molecular solution, micellar solution (Tween-20) and liposomal dispersion (soybean lecithin) was monitored by HPLC. The rate of oxidation of the five polyphenols was higher at pH 4.5 than at pH 3.5. Compared with the control, addition of Tween-20 (micellar structure) and lecithin (liposomal structure) significantly decreased the degradation of polyphenols. In the presence of lecithin the autooxidation of all the five polyphenols was slower than in the presence of Tween-20. The effective protection of the colloidal structures was compared with the hydrophobicity of the polyphenols estimated from the partitioning between octanol and water. The protection from oxidation in the presence of the colloidal structures (micellar or liposomal) increased with increasing partitioning of a polyphenol towards the hydrophobic environment. The protecting effect of the colloidal structures was more effective at pH 4.5 than at pH 3.5.