Effects of pH and palmitic acid on the organization and stability of lutein in the phosphatidylcholine membranes – Spectroscopic studies

Abstract

This paper presents the effect of pH and the presence of palmitic acid (PA) on the organisation and stability of lutein (LUT) in the egg yolk phosphatidylcholine (EYPC) membranes. This is the first known thorough study on the EYPC liposomes formed in different buffers such as acetic at pH 5.0, phosphate at pH 7.4 and borate at pH 9.0. UV–Vis absorption and infra-red (FTIR) spectroscopy were used for molecular studies. Based on analysis of UV–Vis spectra it can be argued that the pH and temperature conditions are crucial for the stability of LUT molecules. After analysing the spectra of samples containing LUT + PA, it can be concluded that the presence of PA in all the applied buffers provides better stability for LUT and perhaps its better solubility. The changes in the absorbance spectrum observed after incubation at 37 °C for 1 h also indicated the beneficial effect of PA presence. Our studies indicate that PA presence in the lipid membranes may have protective effect on LUT, especially at pH 5.0 and that it slows down the degradation process of LUT. Localized pH heterogeneities can induce local dynamical membrane deformations which combined with a certain molecular organization of LUT (such as dimers) can result in lower or higher membrane penetration by LUT molecules.