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Natural Fluorescence of Red and White Wheat Kernels

¹Engineering Research Unit, USDA-ARS, Grain Marketing and Production Research Center, 1515 College Ave, Manhattan, KS 66502. Names are necessary to report factually on available data: however, the USDA neither guarantees not warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be available. ²Corresponding author. Phone: 785-776-2761. Fax: 785-537-5534. E-mail: ramms@gmprc.ksu.edu ³Grain Quality and Structure Research Unit, USDA-ARS, Grain Marketing and Production Research Center, 1515 College Ave, Manhattan, KS 66502.

Red and white wheats must be segregated for marketing purposes because they have different end uses. Identification of wheat color is not straightforward, and currently there is interest in characterizing red and white wheats using spectroscopic methods and chemical tests. The kernels of both red and white wheats exhibit natural fluorescence that can be readily viewed under UV light, although it is not possible to differentiate the fluorescence spectra of red and white wheats by visual inspection only. Fluorescence emission spectra in the wavelength range of 370–670 nm for 91 wheat samples consisting of 48 red (from 30 cultivars) and 43 white (from 18 cultivars) were analyzed by partial least squares (PLS) and neural networks analyses (NNA). Samples included cultivars that were difficult to classify visually as well as wheat harvested after rainfall. Classification accuracies were ≈85% for calibration and ≈72% for the validation samples by both analyses. A plot of β-coefficient vs. wavelength in PLS analysis indicated that fluorescence of red wheat cultivars was greater than that for white wheat cultivars at 425 (±20) nm wavelength. Fluorescence of white wheat cultivars was greater than that for red cultivars at 587 (±35) nm. Fluorescence emission at ≈450 nm from wheat samples increased in intensity after treatment with NaOH. The increase was greater for red than for white wheat. Wheat harvested after rainfall also exhibited a slight increase in fluorescence.