Comparison of hydrolysis methods for removal of glycerides in rice bran acid oil

Abstract

The objective of this study is to determine the suitable hydrolysis method for removal of glycerides in rice bran acid oil based on the percentage of glycerides conversion, remaining content of γ-oryzanol and antioxidant activity. The experiment was divided into two parts. Firstly, three hydrolysis methods consisting of subcritical water hydrolysis, acid-catalyzed hydrolysis and base-catalyzed hydrolysis were compared. The suitable methods were selected and were evaluated in the second part to determine the suitable hydrolysis conditions. Subcritical water hydrolysis and base catalyzed hydrolysis was found to give higher percentage of glycerides conversion than acid catalyzed hydrolysis, while the antioxidant activities of the reaction products obtained from various methods did not differ significantly. Therefore in suitable conditions were then determined for these two methods. Base on the percentage of glycerides conversion and remaining content of γ-oryzanol, the most suitable temperature and time for subcritical water hydrolysis was 200°C and 30 minutes, respectively. At this condition, the percentage of glycerides conversion and the remaining content of γ-oryzanol were 86.49±1.18 and 80.34±1.80 % respectively. For base-catalyzed hydrolysis, the most suitable condition is 2.5N sodium hydroxide solution at 90 °C, and the reaction time between 5 to 10 minutes. At these conditions, glycerides were completely removed and the content of γ-oryzanol remained in hydrolyzed product were 56.48±1.54 % and 65.88±0.25 % for the reaction time of 5 and 10 minutes, respectively. Moreover, the antioxidant activity of hydrolyzed products obtained from base-catalyzed hydrolysis was found to be the higher than that obtained from subcritical water hydrolysis.