Measurement of Single-kernel Wheat Hardness Using Near-infrared Transmittance

Abstract

Near-infrared transmittance spectra (740 to 1140 nm) were gathered on single kernels of intact wheat (Triticum aestivum) for the purpose of establishing the feasibility of measuring wheat hardness (i.e., texture) by spectroscopy. Spectra of kernels from a 10-variety hardness standardization set were modeled using multiple linear regression (MLR) on log(1/T) and d2log(1/T)/dl2 (up to five terms for each) and partial least squares (PLS) analysis (up to nine factors). Near-infrared diffuse reflectance hardnesses, determined by an official method of the American Association of Cereal Chemists, were the reference values. Single-kernel hardness models were then applied to five varieties of wheat excluded in calibration. Results indicated that single-kernel hardness by optical measurement of intact kernels is possible, largely to the extent of the correlation between hardness and vitreousness. Five-term log(1/T) MLR and eight-factor PLS models provided the best modeling performances. Models were then used to examine kernel-to-kernel variation in hardness. By way of example, when the eight-factor PLS model was applied to the standardization set, the variety, Bennett, had the least variation (standard deviation of 5.1 NIR-hardness units), and the variety, Nugaines, had the most (s.d. = 14.9 NIRh.u.). Soft wheats tended to have more variation than hard wheats. Intact-kernel transmittance measurements may lack the sensitivity needed to directly measure the biochemical component (presumably, a low-molecular weight protein) that determines hardness.