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

Regulatory agencies within the USDA have expressed an interest in sing le kernel analysis of grain for determination of basic intrinsic prope rties such as protein content. A study was undertaken to determine the feasibility of measuring protein content of intact wheat kernels usin g near-infrared transmittance spectrophotometry. Six wheat classes wer e examined: hard red winter, hard red spring, hard white, soft red win ter, soft white, and durum. Five samples per class were used, with eac h 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 accur acies of r(2) in the range of 0.85-0.93 and standard errors of predict ion of 0.4-0.9% protein were determined on the validation sets. The nu mber of PLS factors required for optimal model performance ranged from 6 to 14, dependent on wheat class and the type of mathematical transf ormation on the spectra before modeling. Repeatability measurements on kernels that were reloaded into the kernel clamp indicated that the v ariance of model-determined protein content caused by kernel positioni ng was largest for the smaller wheat kernels. Improvement in model per formance could probably be attained by the averaging of transmittances taken from several positions on each kernel.