ESTIMATING RUMINAL PROTEIN DEGRADABILITY OF ROASTED SOYBEANS USING NEAR-INFRARED REFLECTANCE SPECTROSCOPY

Heat treatment by roasting is used extensively in the Midwest to incre ase RUP of whole soybeans (Glycine max L. Merr.). Samples of roasted s oybeans (n = 266) were collected from different suppliers in Wisconsin , Minnesota, and Michigan to determine the value of near infrared refl ectance spectroscopy for estimating RUP. Samples were analyzed for DM, total N, protein dispersibility index, and RUP using an inhibitor in vitro procedure. Samples were milled (1 mm), and near infrared reflect ance spectra were collected. Scans from 121 samples (calibration set) were used to develop calibration equations. Standard errors and coeffi cients of multiple determination for calibration of near infrared refl ectance spectroscopy using conventional chemical assays were, respecti vely, 0.26 and 0.97 (DM), 0.05 and 0.99 (total N), 1.60 and 0.71 (prot ein dispersibility index), and 0.98 and 0.90 (RUP). A validation set o f 145 samples then was used to evaluate the accuracy of calibration eq uations for estimating chemical composition. Standard errors and coeff icients of determination for validation were, respectively, 0.63 and 0 .86 (DM), 0.12 and 0.86 (total N), 3.52 and 0.52 (protein dispersibili ty index), and 1.54 and 0.70 (RUP). Protein dispersibility index was p oorly correlated (r(2) = 0.28) to RUP estimated by inhibitor in vitro. Results indicated that near infrared reflectance spectroscopy might b e used to estimate DM, total N, and RUP in roasted soybeans.