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<sup>-1</sup> and resolution of 16 cm<sup>-1</sup> 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<sup>2</sup><SUB>CAL</sub>), root mean standard error of calibration (RMSE<SUB>CAL</sub>), coefficient of determination for cross-validation (R<sup>2</sup><SUB>CV</sub>), root mean standard error of cross-validation (RMSE<SUB>CV</sub>) 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<SUB>CV</sub> of 0.14. The absorption peaks of the optimal model mainly located at 9402-7492 cm<sup>-1</sup> and 5452-4244 cm<sup>-1</sup>. 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.
Highlights
Sorghum is one of the leading cereal crops worldwide and ranks the fifth highest production of the cereal crops, following maize, wheat, rice, and barley, with 57.6 million tons of annual production globally in 2017 [1]
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), which was calculated by the standard deviation (SD) of the measured composition divided by RMSECV, i.e., RPD=SD/RMSECV
The distribution of tannin contents of the samples exhibited a normal pattern with the most frequent zone of 0.28%-0.35% DM accounting for 40.17% of the sample population, followed by the zones of 0.35%-0.43% DM and 0.21%-0.28% DM
Summary
Sorghum is one of the leading cereal crops worldwide and ranks the fifth highest production of the cereal crops, following maize, wheat, rice, and barley, with 57.6 million tons of annual production globally in 2017 [1]. Because of the superior agronomic attributes, nutrient value and health potential, sorghum has attracted increasing attention from academia and industries in the past decades. As well, it has been used as feedstuff in livestock production with the advantages of high energy value and relatively low price [4,5,6]. The intrinsic tannin in sorghum grains acts as a double-edged sword in animal nutrition, i.e., a proper dose of dietary tannin would exert a positive effect on animal health and production, whereas exceeding dose may cause certain deleterious effects such as reduced feed intake, nutrient digestibility, growth performance and poor gastrointestinal health, acting as an antinutritional factor [7]. To optimize the utilization of sorghum in animal production, there is a need for a precise
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