Graduate Thesis Or Dissertation
 

Some flavor components of wheat

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  • The volatile flavor fraction of lightly milled wheat grown in eastern Oregon was isolated for study by two methods: steam distillation under vacuum and steam distillation at atmospheric pressure. The sample obtained under vacuum was extracted with ether which was then evaporated to yield the desired wheat essence. Steam distillation at atmospheric pressure provided the headspace vapors that were used for a portion of the gas chromatographic analysis. Identification of the organic substances contained in the volatile flavor fraction was made on the basis of chemical tests, paper chromatography, gas-liquid chromatography, and mass spectrometry. Preliminary testing for amines and carbonyls indicated the presence of both of these functional groups, although in subsequent research amines were not detected. Additional information as to the functional groups present was obtained by subjecting headspace vapor samples to gas chromatography and directing the column effluent into vials containing reagents selected to indicate the presence of alcohols, amines, esters, carbonyls, and mercaptans. A separate set of reagents was used for each eluting peak. Formation of 2, 4-dinitrophenylhydrazone derivatives and determination of their melting points provided one means of tentative identification of carbonyl compounds. Ascending paper chromatography was used to separate the 2, 4-dinitrophenylhydrazone derivatives of the carbonyls into classes and to ultimately assist in the identification of these compounds. A Barber-Colman gas-liquid chromatograph equipped with a flame ionization detector was used as a means of separating the components in the samples. Identification of some of the compounds was possible through comparisons of retention times of the peaks on these columns with retention times of known compounds. Column packings used for gas-liquid chromatography were six percent Apiezon M, six percent Diethylene Glycol Succinate, and three percent Free Fatty Acid Phase, all on a solid support of Anakrom ABS, 90 to 100 mesh. The column was heated isothermally at 75°C with nitrogen as the carrier gas flowing at a pressure of five pounds per square inch. Mass spectra of the wheat essence compounds were obtained by use of an Atlas-MAT Ch-4 mass spectrometer using a two second scan, coupled with a gas-liquid chromatograph. Twelve compounds were identified and six were tentatively identified in the headspace aroma or in the wheat flavor essence. Those identified were acetaldehyde, isobutyraldehyde, butyraldehyde, valeraldehyde, hexanal, heptanal, octanal, crotonaldehyde, 3-methyl-2-butanone, 2, 2-dimethyl-3-pentanone, diacetyl, and ethyl acetate. The compounds tentatively identified included isoamyl alcohol, amyl alcohol, butanone, isovaleraldehyde, cyclopentanone, and phenylacetaldehyde.
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