SINGLE WHEAT KERNEL ANALYSIS BY NEAR-INFRARED TRANSMITTANCE - PROTEIN-CONTENT

Regulatory agencies within the USDA have expressed an interest in single kernel analysis of grain for determination of basic intrinsic properties such as protein content. A study was undertaken to determine the feasibility of measuring protein content of intact wheat kernels using near-infrared transmittance spectrophotometry. Six wheat classes were examined: hard red winter, hard red spring, hard white, soft red winter, soft white, and durum. Five samples per class were used, with each sample represented by 96 randomly drawn kernels. Within each class, single kernel spectra (850-1,050 nm) were calibrated to single kernel protein content using four samples; the remaining sample was set aside for model validation. The chemometric method of partial least squares (PLS) analysis was used. For reference values, the protein content (N X 5.7) of each kernel was measured by combustion. Typical model accuracies of r(2) in the range of 0.85-0.93 and standard errors of prediction of 0.4-0.9% protein were determined on the validation sets. The number of PLS factors required for optimal model performance ranged from 6 to 14, dependent on wheat class and the type of mathematical transformation on the spectra before modeling. Repeatability measurements on kernels that were reloaded into the kernel clamp indicated that the variance of model-determined protein content caused by kernel positioning was largest for the smaller wheat kernels. Improvement in model performance could probably be attained by the averaging of transmittances taken from several positions on each kernel.