Estimating the amino acid composition in milled rice

This study was conducted to develop near-infrared reflectance spectroscopy (NIRS) equations to predict the amino acids and nitrogen content of milled rice powder. The samples were scanned by NIRS, and analyzed for amino acid composition and total nitrogen by HCl hydrolysis-HPLC methodology and Kjeldahl method, respectively. The NIRS equations of fifteen different amino acids, except for cystine, methionine and histidine, showed high coefficient of determination (RSQ = 84.8%97.5%) and low standard errors in calibration with 3g samples for NIRS scanning, while the calibration models of cystine and histidine could explain less variation (RSQ with 77.7% and 65.0%). Calibration for methionine was not suitable to estimate methionine because of its very low RSQ (10.2%). The equations for total amino acids and nitrogen also showed high RSQ and lower standard error in calibration, respectively. Furthermore, calibration equations developed with only about 500mg-sample showed similar accuracy and reliability to those with the full-cup by using the same calibration set. The equations developed for relative contents of total amino acids did not show good, effective calibration and cross validation. Only eight different amino acids can be predicted because their RSQs of calibration were acceptable being higher than 50.6% (50.673.9%) while the others cannot be estimated with confidence by their relative contents due to lower RSQ in calibration. Anyway, their relative contents can be calculated from their absolute contents estimated by NIRS calibration. Key words: Rice; Amino acid; Near-infrared reflectance spectroscopy (NIRS); Nutrition quality 福斯近红外快速品质分析仪