Discrimination of the Geographical Origin of Soybeans Using NMR-Based Metabolomics

Abstract

With the increase in soybean trade between countries, the intentional mislabeling of the origin of soybeans has become a serious problem worldwide. In this study, metabolic profiling of soybeans from the Republic of Korea and China was performed by nuclear magnetic resonance (NMR) spectroscopy coupled with multivariate statistical analysis to predict the geographical origin of soybeans. The optimal orthogonal partial least squares-discriminant analysis (OPLS-DA) model was obtained using total area normalization and unit variance (UV) scaling, without applying the variable influences on projection (VIP) cut-off value, resulting in 96.9% sensitivity, 94.4% specificity, and 95.6% accuracy in the leave-one-out cross validation (LOO-CV) test for discriminating between Korean and Chinese soybeans. Soybeans from the northeastern, middle, and southern regions of China were successfully differentiated by standardized area normalization and UV scaling with a VIP cut-off value of 1.0, resulting in 100% sensitivity, 91.7%-100% specificity, and 94.4%-100% accuracy in a LOO-CV test. The methods employed in this study can be used to obtain essential information for the authentication of soybean samples from diverse geographical locations in future studies.

Keywords: Glycine max; NMR; geographical location; metabolic profiling; prediction.

Figure 1

OPLS-DA score plots (A) derived from the ¹H-NMR spectra of soybean samples for discriminating geographical origin, Korea and China. Leave-one-out cross-validated score plots (B) showing Korean soybeans (above dashed line) and Chinese soybeans (below dashed line) with threshold value of 0.5 (dashed line) for all samples. In case of misclassified samples, the Ypredcv values were marked with red circles.

Figure 2

PLS-DA score plots (A) derived from the ¹H-NMR spectra of soybean samples for discriminating the geographical origin of three regions of China. Leave-one-out cross-validated score plots for NR vs. MR/SR comparative group (B), MR vs. NR/SR comparative group (C), and SR vs. NR/MR comparative group (D) showing control sample (one region, above dashed line) and case sample (two regions, below dashed line) with threshold value of 0.5 (dashed line) for all samples. In case of misclassified samples, the Ypredcv values were marked with red circles. NR: northeastern region, MR: middle region (Huang-Huai-Hai and Yangtze River region), SR: southern region.