Analysis of alkylresorcinols in wheat germ oil and barley germ oil via HPLC and flourescence detection: Cochromatography with tocols

Authors: Moreau, Robert; FANG, XUEZHI - Chinese Academy Of Forestry

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2015
Publication Date: 5/10/2016
Publication URL: http://handle.nal.usda.gov/10113/62498
Citation: Moreau, R.A., Fang, X. 2016. Analysis of alkylresorcinols in wheat germ oil and barley germ oil via HPLC and flourescence detection: Cochromatography with tocols. Cereal Chemistry. 93(3):293-298.

Interpretive Summary: Wheat germ oil is considered to be healthy oil mainly because it contains high levels of antioxidants, especially vitamin E. This manuscript reports for the first time that commercial wheat germ oil also contains a second type of antioxidants called alkylresorcinols, which previously have been reported to occur in high levels in wheat bran and in foods that contain whole grains such as wheat, rye, or barley. This manuscript also reports that a new sensitive method that was recently reported to be useful for the analysis of alkylresorcinols also contains peaks of other unknown compounds. The authors showed that three of these unknown peaks in wheat germ oil were tocopherols (vitamin E derivatives) and that two of alkylresorcinol peaks also may contain other fluorescent phytonutrients called tocotrienols. This manuscript confirms the value of the previously reported HPLC method but it advises analysts that the use of the method with some experimental materials may require careful interpretation of the experimental data.

Technical Abstract: Alkylresorcinols are long chain phenolic compounds that have been reported to be localized in the outer layers of the kernels of wheat, rye, barley and other grains. A sensitive HPLC method with fluorescence detection was recently reported for the quantitative analysis of alkylresorcinols in cereal grains and products. Using this new HPLC method we report for the first time that wheat germ oil contains moderate levels of alkylresorcinols, approximately 800-1500 µg per gram of oil. We also found that commercial wheat germ oil and some experimental samples of wheat germ oil and barley germ oil also contain three unknown peaks. Upon further evaluation of these peaks it was found that the peaks are tocopherols (one peak of a tocopherol, one peak of d-tocopherol and a peak with the combination of ß and '-tocopherol), even though the excitation and emission wavelengths for alkylresorcinols (ex 274 nm/em 300 nm) are different than those for tocols (ex 294 nm/em 326 nm). We also found that with this HPLC system one alkylresorcinol, AR17, has the same retention time (7.6 min) as d-tocotrienol and another alkylresorcinol, AR19, has the same retention time (10.8 min) as a tocotrienol. Using this new HPLC system to analyze alkylresorcinols in five corn genotypes, we detected three fluorescent peaks but we concluded that only one of these peaks contained both AR19 and a tocotrienol. Similarly, we attempted to use this new HPLC system to analyze alkylresorcinols in four sorghum genotypes and one of the fluorescent peaks had the correct retention time for an alkylresorcinol and one had the correct retention time for '-tocopherol, but several other fluorescent peaks did not correspond to any standards.