Effective Quantification of Tannin Content in Sorghum Grains Using Near-infrared Spectroscopy

Abstract

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 (Nc=77 samples) and a prediction set (Np=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 (R2CAL), root mean standard error of calibration (RMSECAL), coefficient of determination for cross-validation (R2CV), root mean standard error of cross-validation (RMSECV) 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 RMSECV 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.