High-resolution nuclear magnetic resonance and near-infrared determination of soybean oil, protein, and amino acid residues in soybean seeds.

We present a detailed account of our high-resolution nuclear magnetic resonance (HR-NMR) and near-infrared (NIR) calibration models, methodologies, and validation procedures, together with a large number of compositional analyses for soybean seeds. NIR calibrations were developed based on both HR-NMR and analytical chemistry reference data for oil and 12 amino acid residues in mature soybeans and soybean embryos. This is the first report of HR-NMR determinations of amino acid profiles of proteins from whole soybean seeds, without protein extraction from the seed. The best results for both oil and protein calibrations were obtained with a partial least squares regression (PLS-1) analysis of our extensive NIR spectral data, acquired with either a DA7000 Dual Diode Array (Si and InGaAs detectors) instrument or with several Fourier transform NIR (FT-NIR) spectrometers equipped with an integrating sphere/InGaAs detector accessory. To extend the bulk soybean samples calibration models to the analysis of single soybean seeds, we analyzed in detail the component NIR spectra of all major soybean constituents through spectral deconvolutions for bulk, single, and powdered soybean seeds. Baseline variations and light-scattering effects in the NIR spectra were corrected by calculating the first-order derivatives of the spectra and the multiplicative scattering correction (MSC), respectively. The single soybean seed NIR spectra are broadly similar to those of bulk whole soybeans, with the exception of minor peaks in single soybean NIR spectra in the region from 950 to 1000 nm. On the basis of previous experience with bulk soybean NIR calibrations, the PLS-1 calibration model that we developed for single soybean seed analysis was selected for protein, oil, and moisture calibrations. To improve the reliability and robustness of our calibrations with the PLS-1 model, we employed standard samples with a wide range of soybean constituent compositions: from 34 to 55% for protein, from 11 to 22% for oil, and from 2 to 16% for moisture. Such calibrations are characterized Copyright © 2004 AOCS Press by low standard errors and high degrees of correlation for all major soybean constituents. Moreover, we obtained highly resolved NIR chemical images for selected regions of mature soybean embryos that allow for the quantitation of oil and protein components. Recent developments in high-resolution FT-NIR microspectroscopy extend the NIR sensitivity range to the picogram level, with submicron spatial resolution in the component distribution throughout intact soybean seeds and embryos. Such developments are potentially important for biotechnology applications that require rapid and ultrasensitive analyses, such as those concerned with high-content microarrays in genomics and proteomics research. Other important applications of FT-NIR microspectroscopy are envisaged in biomedical research aimed at cancer prevention, the early detection of tumors by NIR-fluorescence, and identification of single cancer cells or single virus particles in vivo by superresolution microscopy/microspectroscopy.