Comparative study on physicochemical hydrolysis methods for glycerides removal from rice bran acid oil for subsequent γ-oryzanol recovery

A comparative study on physicochemical hydrolysis methods, including acid-catalyzed, base-catalyzed, and subcritical water hydrolysis, for glycerides removal prior to subsequent γ-oryzanol purification from rice bran acid oil (RBAO), is presented. The effects of hydrolysis conditions on the residual levels of glycerides and γ-oryzanol in RBAO were first investigated for each method. It can be concluded that the acid-catalyzed hydrolysis was not a suitable hydrolysis method for this application as it provided a low glycerides conversion level of ca. 30% using 2 N H2SO4 at 80–100 °C, despite the long reaction time (> 60 min). For the base-catalyzed hydrolysis, 100% glycerides removal was achieved at the most suitable condition, which was suggested to be at 2.5 N NaOH, 90 °C and 5–10 min. At this condition, a relatively high residual level of γ-oryzanol of ca. 57–66% was obtained. For the subcritical water hydrolysis, the results suggested that γ-oryzanol was hydrolyzed more rapidly than glycerides, and the most suitable condition for subcritical water hydrolysis was at 220 °C for 10 min. At this condition, high glycerides removal of > 95% was achieved while the remaining amount of γ-oryzanol was still acceptable (50%).