Abstract: A method of determining relative polyphenol antioxidant levels in plant matter, particularly whole sorghum seeds, is carried out by combining a selected amount of solid plant matter to be evaluated with a solvent and a polyphenol extraction agent to form a stirrable mixture. The mixture is heated to approximately the boiling point of the solvent with agitation of the mixture for a period of at least 1½ hours. The heated mixture is filtered while the liquid is at a temperature of not more than 5° C. below the boiling point of the solvent to obtain an extractant solution filtrate. From this filtrate, a concentrated extractant solution is formed, cooled, and filtered to form a final filtrate. An analytical sample of this final filtrate is then introduced into a high performance liquid chromatography (HPLC) system to separate and determine the relative amounts of polyphenol antioxidants in the plant matter.