Development of transparent curcumin loaded microemulsions by phase inversion temperature (PIT) method: effect of lipid type and physical state on curcumin stability

In this study, curcumin loaded transparent microemulsions obtained using the phase inversion temperature (PIT) method were developed. Different lipids (sunflower, peanut, castor, and extra virgin olive oil, tristearin, and tripalmitin) were tested as curcumin carrier in microemulsions. The obtained systems were analyzed for transparency, particle size, lipid crystal polymorphism, and curcumin stability at 20 A degrees C up to 120 days. It was found that the maximum lipid content allowing transparent microemulsions (mean particle diameter of around 25 nm) to be obtained was greatly affected by the lipid characteristics. By using oils rich in long chain fatty acids, such as sunflower, peanut, and extra virgin olive oil, transparent microemulsions can be obtained with oil fractions up to 7.5 % (w/w). On the contrary, when fat containing crystals (e.g. tripalmitin or tristearin) was used, the maximum lipid loading capacity was reduced to 5 % (w/w). Castor oil, rich in polar groups, did not permit the formation of transparent microemulsions at any tested concentration (from 1 to 9 % w/w). The oil type also affected curcumin stability: curcumin degradation rate was lower in tristearin containing microemulsions than in those containing extra virgin olive oil. This result was attributed to the protective effect of solid lipid particles into lipid droplets.