Effect of colloidal structures on the stability of five flavonoids with different hydrophilicity

Autoxidation of five flavonoids representing range of different hydrophilicities (epicatechin gallate (ECG), (+) 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 oxidaton of the five flavonoids 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 flavonoids. In the presence of lecithin the autoxidation of all the five flavonoids was slower than in the presence of Tween-20. The effective protection of the colloidal structures was compared the hydrophilicity of the flavonoids 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 flavonoid towards the hydrophobic environment. The protecting effect of the colloidal structures was more effective at pH 4.5 than at pH 3.5.