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Estimation of Free Glycolipids in Wheat Flour by HPLC¹

¹Cooperative investigations, U. S. Department of Agriculture, Agricultural Research Service, and the Department of Grain Science and Industry, Kansas State University. Contribution No. 98-479-J from the Kansas Agricultural Experiment Station, Manhattan, KS 66506. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. ²Graduate research assistant and professor, respectively, Department of Grain Science and Industry, Kansas State University, Manhattan, KS 66506. ³Postdoctoral research chemist, and supervisory research chemist, respectively, USDA-ARS, Grain Marketing & Production Research Center, Manhattan, KS 66502. ⁴Corresponding author. E-mail: okchung@usgmrl.ksu.edu Phone: 785-776-2703. Fax: 785-776-2792.

The chloroform-acetone mixture (4:1, v/v) was an effective solvent for eluting the nonpolar lipid fraction, including free fatty acids, from the polar lipid (glycolipid and phospholipid) fractions from free lipids of 21 hard winter wheat flours using a solid-phase extraction system. Amounts of monogalactosyldiglycerides (MGDG) and digalactosyldiglycerides (DGDG) in the glycolipid fraction were determined by normal-phase HPLC with a gradient system using an evaporative light-scattering detector (ELSD) and a diode array detectors (DAD). Unsaturated fatty acids showed higher UV absorbances from 200 to 213 nm when compared with saturated palmitic acid. However, significant linear correlation coefficients were obtained between the peak areas measured by a DAD and GL contents determined by an ELSD, suggesting that fatty acid composition of flour GL could be fairly constant. Using an ELSD as a reference, equations for determination of MGDG or DGDG quantities were derived from the peak areas of a DAD by multivariate regression methods. Determination of MGDG and DGDG quantities was also possible using only a DAD.