Photostability studies of retinyl palmitate entrapped in policosanol oleogel matrices

Abstract

Photostability of all-trans retinyl palmitate (RP) (100% bioactivity) was studied in policosanol oleogels (PCOs) matrices (7%, 10%, and 12%, w/w, policosanol in soybean oil) after UVA irradiation. RP was incorporated into PCOs at levels of 0.04%, 0.1% and 1% (w/w). PCOs efficiently protected RP from UVA-mediated degradation. Over 75% RPactivity remained in PCOs after 4 days of UVA irradiation, while only 12% RP-activity remained in soybean oil. HPLC analysis showed that cis-RP was formed in liquid soybean oil after 2 days of UVA irradiation while it was absent in PCOs matrices. PCOs blocked the energy absorption from UVA and further dampened the UVA-mediated ionic photodissociation and free radical reaction due to matrix immobilization. For all samples, RP photodegradation followed a 2 nd order reaction. From the reaction kinetics, it would be possible to predict the RP photodegradation rate in PCO matrices. PCOs were shown to be a promising matrix to efficiently protect RP from photodegradation.