Non-destructive Measurement of Potassium Content in Low-Potassium Radish and Turnip Using Visible Near-Infrared Spectroscopy

This study aimed to devise a non-destructive method to measure the potassium content of root vegetables using visible and near-infrared spectroscopy. The test materials included three varieties of radish, i.e., “New Comet”, “Isabell”, and “Ruby Comet”, and “Mifune” turnips. Visible light reflectance (400-700 nm) and near-infrared light reflectance (1,100-1,350 nm) of the embryo axes were measured, and analyzed using second-order derivatives. The actual potassium content was measured using an inductively coupled plasma emission spectrometer. Calibration curves were created using partial least squares regression analysis, and the predicted values were calculated. The correlation coefficients between the predicted and actual values were as follows: 0.801 for “New Comet”, 0.698 for “Isabell”, 0.820 for “Ruby Comet”, and 0.805 for “Mifune”; thus, a high correlation was observed for all tested varieties. The ‘ratio of standard deviation of reference data in prediction sample set to standard error of prediction (RPD)’, which determined the analytical precision of the calibration curve, were 11.0, 4.24, 4.58, and 5.92 for “New Comet”, “Isabell”, “Ruby Comet”, and “Mifune”, respectively. Therefore, non-destructive measurement of potassium content is possible using visible and near-infrared spectroscopy.