Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 1, 2003
Publication Date: February 1, 2003
Citation: RAM, M.S., DOWELL, F.E., SEITZ, L.M. FT-RAMAN SPECTRA OF UNSOAKED AND NAOH-SOAKED WHEAT KERNELS, BRAN AND FERULIC ACID. CEREAL CHEMISTRY. 2003. 80(2):188-192. Interpretive Summary: Red and white wheats must be kept separate to avoid discounts that usually apply when wheats with mixed colors are marketed. A sodium hydroxide (NaOH) test for determining wheat color class depends on the observation that upon soaking in NaOH, red wheat turns a darker red and white wheat turns straw yellow. To investigate the mechanism of this test, spectra of molecules in wheat bran and whole kernels of wheat (before and after NaOH treatment) were obtained by the Raman technique. When kernels were soaked in NaOH, shifts in color were consistent with chemical changes in a compound called ferulic acid. Further investigations are needed to elucidate the mechanism of the NaOH test. Understanding the mechanism will aid development of improved methods for wheat color classification.
Technical Abstract: The sodium hydroxide (NaOH) test for determining wheat color class depends on the observation that upon soaking in NaOH, red wheat turns a darker red and white wheat turns straw yellow. To understand the mechanism of this test, Raman spectra of wheat bran, wheat starch, ferulic acid, and whole kernels of wheat, before and after NaOH soak, were studied. The major observable components in the whole kernel were that of starch, protein, and ferulic acid, perhaps esterified to arabinoxyland and sterols. When kernels are soaked in NaOH, spectral bands due to ferulic acid shift to lower energy and show a slight-reduced intensity which is consistent with deprotonation of the phenolic group and extraction of a potion of the ferulic acid into solution. Other phenolic acids, alkyl resorcinols, and flavonoids found in the NaOH extracts of what by high performance liquid-chromatography were not observed in the Raman spectra. Wheat bran accounts for most of the ferulic acid in the whole kernel, as indicated by the increased intensity of the doublet at 1631 and 1600 1/cm in the bran. The intense starch band at 480 1/cm found in the whole kernel of wheat was nearly absent in the wheat bran.