Evaluation of operating conditions for surface lipid extraction from rice using a Soxtec system

The degree of milling (DOM) of rice is a measure of how well the germ and bran layers are removed from the surface of rice kernels during milling. Because the majority of rice kernel lipids are found on the surface, measuring the surface lipid content (SLC) of rice after milling may be one way to quantify the DOM of rice. While there are several methods to measure the lipid content (LC) of rice, there is not an established standard method for determining the SLC of milled rice. The objective of this study was to evaluate the primary operating variables of a Soxtec apparatus in measuring the SLC of milled rice. This was accomplished by varying the preextraction drying, boiling, rinsing, and postextraction drying durations, as well as the solvent used for extraction, to achieve the maximum extraction of lipids from rice. Experiments were performed on stored Oryza sativa L. 'Cypress' and 'Bengal' rice milled for 10, 30, and 60 sec. Results showed that durations of 1 hr of preextraction, 20 min of boiling, 30 min of rinsing, and 30 min of postextraction drying provided the maximum lipid extraction from milled head rice with petroleum ether. Of the three solvents tested, petroleum ether, and ethyl ether yielded similar extraction results.