Preparation, optimization using a mixture design, and characterization of a novel astaxanthin-loaded rice bran oil self-microemulsifying delivery system formulation

This research aimed to develop a self-microemulsifying delivery system (SMEDS) to increase dissolution rate of astaxanthin (AST) using a design of experiment (DoE) approach for investigating the effect of components on the physicochemical properties of AST SMEDS formulation. By applying the mixture design, the optimal compositions of rice bran (RB) oil (oil; X1), Kolliphor® RH40 (surfactant; X2), and Span® 20 (cosurfactant; X3) were determined based on the preliminary screening studies. The optimization models were validated by comparing the regression coefficient (R2) of the predicted values to the experimentally measured ones. Based on the desirability function, the optimized AST SMEDS was composed of 33.67% rice bran oil, 34.70% Kolliphor® RH40, and 31.63% Span® 20 which contained AST concentration (Y1) of 0.04% in the formulation and yielded microemulsion droplet size (Y2) of 40.79 ± 3.11 nm. The experimentally measured values obtained from the optimized AST SMEDS were in accordance with its predicted values with relatively low prediction errors (< 2%). The validated models were investigated by the contour plots, three-dimensional surface plots, and main effect plots. It was found that surfactant and cosurfactant inversely affected on droplet size changes whereas all three components (oil, surfactant and cosurfactant) did not relatively impact AST solubilizing capacity. In vitro release of AST SMEDS was significantly increased more than 90% compared to the raw AST powder. The optimized AST SMEDS was successfully developed by the mixture design and could be economically effective to enhance dissolution of poorly water-soluble AST.