Enzymatic pretreatment of rice bran acid oil before γ-oryzanol recovery

Abstract

This study aims to apply enzymatic reactions for pretreating the major byproduct of rice bran oil (RBO) industry, rice bran acid oil (RBAO) before γ-oryzanol recovery. RBAO contains free fatty acids (FFAs), glycerides, and is rich in the super-antioxidant, γ-oryzanol. As a primary step to recover γ-oryzanol from RBAO, glycerides must be removed because of having similar polarity with γ-oryzanol. This study is conducted in two parts, hydrolysis and esterification/transesterification. In the first part, enzymatic hydrolysis. The study evaluates the performance of operating conditions using one factor at a time (OFAT) on the reaction time, temperature, lipase loading, water:RBAO ratio, and speed where glycerides removal and γ-oryzanol loss are measured as responses. From these, Face-centered central composite rotatable design (FCCD) was used to investigate the effects of three independent variables: time, temperature, and water:RBAO ratio, and their interactions on the responses: glyceride removal, γ-oryzanol loss, and FFAs production, and to determine the statistical models describing their relationships. In addition, by applying the desirability function approach, the optimal location was identified, corresponding to maximal glyceride removal with an imposed upper limit of 35% γ-oryzanol loss. Lastly, the last section is the confirmation of the validity of the model and at an established optimal condition of 22 h, 48.5 °C and 1:1 water:RBAO ratio, confirmed the validity of the models: glyceride removal approached completion (99%), γ-oryzanol loss was as low as 32%, and the FFAs production was 73–75%. Then the second part is enzymatic esterification/transesterification. First is to evaluate the performance of operating conditions using OFAT of ethanol to RBAO molar ratio, temperature, time of reaction, lipase loading, and speed on the glycerides removal, Fatty acid ethyl ester (FAEE/biodiesel), γ-oryzanol loss, and FFAs remaining. Two optimal conditions at 40°C, 3:1 and 5:1 mol ratio of ethanol to RBAO,10% of lipase loading,200 rpm, and 18 and 24 h reaction time, respectively with >98% glyceride removal. Then, the extraction of γ-oryzanol from FAEE using aqueous ethanolic NaOH is conducted and resultant that around 90% of γ-oryzanol can be extracted at 2M. As a primary step to recover γ-oryzanol from RBAO, glycerides must be removed by conversion into more easily separable components such as FFAs or FAEE. The results of this study demonstrated that enzymatic hydrolysis and esterification/transesterification are promising methods for glyceride removal prior to recovery of γ-oryzanol from RBAO and that the statistical models gave accurate predictions of responses and would be useful for further industrial design of the process also is environmentally friendly biocatalysts. Further modifications in the process may be needed to reduce the content of glycerides. Moreover, the losses of γ-oryzanol from these two methods are much better than the conventional method and are interesting to explore further.