This study was conducted to investigate the feasibility of determining tannin content in sorghum grains with near-infrared reflectance spectroscopy (NIRS). A total of 110 sorghum grain samples were collected. The data matrix of the pretreated NIRS was randomly divided into a calibration set (N_c=77 samples) and a prediction set (N_p=33 samples). The analysis of tannin content was based on the colorimetric method of GBT 15686-2008. Diffuse reflectance spectra of 110 sorghum samples were generated on a Fourier-transform NIRS with a scanning range of 12800-4000 cm~(-1) and resolution of 16 cm~(-1) and 64 scans. Several spectra pretreatment methods were compared to for an optimum spectral pretreatment method. The optimal model was determined according to coefficient of determination for calibration (R~2_(CAL)), root mean standard error of calibration (RMSE_(CAL)), coefficient of determination for cross-validation (R~2_(CV)), root mean standard error of cross-validation (RMSE_(CV)) and the residual predictive deviation (RPD). The results showed that the tannin content of the sorghum grains ranged from 0.01% to 2.12% DM with the average of 0.58%, and first derivative was the optimal spectral pretreatment with the lowest RMSE_(CV) of 0.14. The absorption peaks of the optimal model mainly located at 9402-7492 cm~(-1) and 5452-4244 cm~(-1). The RPD of calibration, cross-validation and external validation were 6.22, 4.22 and 3.0, respectively. The findings suggest that the established model using NIRS is effective to quantify tannin content in sorghum grains rapidly.
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