Date of Award

1998

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

School of Nutrition and Food Sciences

First Advisor

J. Samuel Godber

Abstract

A high purity $\gamma$-oryzanol was obtained from crude rice bran oil using a normal phase preparative scale HPLC. It was used in implementing a reverse phase HPLC method for separating each individual component of $\gamma$-oryzanol present in rice bran oil. Ten fractions were isolated in the reverse phase HPLC method. The ten components of $\gamma$-oryzanol were identified. Three of these, cycloartenyl ferulate, 24-methylene cycloartanyl ferulate, and campesteryl ferulate, were major components of $\gamma$-oryzanol. The yield of $\gamma$-oryzanol without saponification was significantly higher than that with saponification in solvent extraction. The solvent mixture with 50% hexane and 50% isopropanol (v/v.) at an temperature of 60$\sp\circ$C for 60 min produced the highest yield of $\gamma$-oryzanol among test solvents and conditions. However, the yield of $\gamma$-oryzanol in supercritical fluid extraction under temperature 50$\sp\circ$C, pressure 680 atm, and time 25 min was approximately four times higher than the highest yield of solvent extraction. Also, high concentration of $\gamma$-oryzanol in extract (50-80%) was obtained by collecting the extract between 15-20 min of extraction under this optimized condition. A quantitative method for determining four hydroperoxide isomers of linoleic acid, 9HPODE(t,c), 9HPODE(t,t), 13HPODE(c,t), and 13HPODE(t,t), using a normal phase HPLC with a UV detector was developed. The sensitivity and specificity of the HPLC method were sufficient to measure the production of the four hydroperoxide isomers when linoleic acid was incubated at 37$\sp\circ$C with constant air flow. $\alpha$-Tocopherol and ferulic acid showed significant antioxidant activity via low productions of hydroperoxides, compared to control. Based on the relative production of each hydroperoxide, the mechanisms of antioxidants, scavenging singlet oxygen or scavenging peroxyl free radicals, were also determined. Different profiles of production of each hydroperoxide in the linoleic acid model with $\alpha$-tocopherol and ferulic acid indicated that they possess different mechanisms of antioxidation. The three components of $\gamma$-oryzanol evidenced significant antioxidant activity when they were mixed with linoleic acid in a molar ratio of 1:100 and 1:250 but not in a molar ratio of 1:500. The antioxidant mechanisms of the three major components of $\gamma$-oryzanol were similar to that of ferulic acid.

ISBN

9780591766790

Pages

98

Share

COinS