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Volatile organic compound profile of whole grain soft winter wheat
T. JI (1), M. Kang (2), B. Baik (3) (1) USDA ARS, , U.S.A.; (2) USDA-ARS-CSWQRU/RDA-NICS Korea, , U.S.A.; (3) USDA-ARS-CSWQRU, , U.S.A..

Grain aroma, which is produced by volatile organic compounds (VOCs), is an indicator of grain soundness and a crucial quality attribute, especially for whole grain foods. The VOC profile of wheat grain is, however, either incomplete or has been determined from grain subjected to climatic and disease factors before harvest. To identify the intrinsic VOC profile of wheat grain, grain of nine soft winter wheat varieties was collected at 20, 25, 30, 35, and 40 days post-anthesis (DPA) and analyzed for VOCs using headspace solid-phase microextraction and gas chromatography. Ten compounds, including ethanol, 2-propanone, 2-butanol, 2-methyl-1-propanol, 3-methyl-1-butanol, 2-methyl-1-butanol, 1-pentanol, hexanal, 1-hexanol, and 2-ethyl-1-hexanol, were detected in all nine varieties at all of the DPAs. Five predominant compounds, including 3-methyl-1-butanol, 2-methyl-1-butanol, 1-pentanol, hexanal, and 1-hexanol were determined to be the major VOCs of soft winter wheat grain and quantified as the benchmark VOCs. The concentrations of VOCs were highest at 20 or 25 DPA and decreased with further maturation, except 1-hexanol. Hexanal was the most abundant VOC in five varieties, and 1-Hexanol in four varieties at 40 DPA. Both hexanal and 1-hexanol exhibited significant variation in concentration among wheat varieties, ranging from 1.30 to 2.99 and 1.21 to 5.46 µg/kg of wheat grain at 40 DPA, respectively. Wheat grain stored for a month, pre-harvest sprouted or infected with powdery mildew, scab, or sooty mold exhibited a prominent VOC peak of 2-ethyl-1-hexanol, 1-hexanol, 1-octen-3-ol, hexanal or 3-methylbutanal, respectively. The intrinsic VOC profile of wheat grain could be used as a reference in the determination of soundness for grain with undesirable odor, or that exposed to fungal infection, pre-harvest sprout damage or grain spoilage during storage.