Investigation of process parameters to enhance the recovery of -oryzanol from rice bran acid oil using full factorial design with the steepest ascent method

g-Oryzanol (OZ) is an antioxidant that has been widely used in the food, cosmetic and pharmaceutical industries. Rice bran acid oil (RBAO), an inexpensive byproduct of rice bran oil (RBO) refining is a rich source of OZ. The recovery of OZ from fatty acid ethyl ester (FAEE) prepared from (RBAO) is presented using an acid-base extraction method. Full factorial design (FFD) was used to determine the factors and their interactions that significantly affected the yield of OZ and FAEE. Three factors, including NaOH concentration (A), % ethanol (B), and % hexane (C) in the total volume of hexane and aqueous ethanol, were investigated and analyzed statistically. The results showed that the main factors and their interactions (except the AC) affected the yield of g-oryzanol, while the yield of FAEE was only affected by the A and AC. Thus, to enhance OZ yield and minimize the loss of FAEE caused by alkali hydrolysis, the significant factors were further optimized using the steepest ascent method. The optimum condition was achieved as follows: 1.8 M of NaOH, 76% of ethanol, and 20.5% of hexane, resulting in the maximum yields of OZ and FAEE of 76.51% and 59.04%, respectively. The results indicated that the presented method is simple, rapid, and effective for recovery of OZ from RBAO. In addition, the FFD and steepest ascent method were useful tools for investigating the process parameters for enhancing the added value of RBAO.