Qualitative and Quantitative Analysis of Sorghum Grain Composition Including Protein and Tannins Using ATR-FTIR Spectros
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Qualitative and Quantitative Analysis of Sorghum Grain Composition Including Protein and Tannins Using ATR-FTIR Spectroscopy H. Lin 1 & S. R. Bean 1
&
M. Tilley 1 & K. H. S. Peiris 2 & D. Brabec 1
Received: 8 April 2020 / Accepted: 5 October 2020 # This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2020
Abstract Chemical composition and grain quality traits are important factors related to the end-use quality of sorghum. Thus, rapid and non-destructive analytical methods for screening sorghum for desirable grain quality traits benefit the industries using sorghum for food, feed, and biofuels as well as sorghum breeders and seed companies working to improve the grain quality of sorghum. In the present study, a method based on Fourier-transform infrared spectroscopy (FTIR) was developed to characterize the major chemical components in sorghum flour. Sorghum flour had three major FTIR active regions from 1800 to 800 cm−1. As expected, FTIR spectra revealed that starch was the primary compound in sorghum flour, followed by protein with only minor amounts of lipids and phenolic acids. Phenolic acids were characterized by a peak at 1709 cm−1, which varied in intensity across sorghum varieties. Tannin sorghum could be discriminated from non-tannin sorghum by a shift in O–H stretch band around 3300 cm−1 and their C=C absorption peaks at 1608 and 1522 cm−1. Flour from the outer part of the kernel (corneous endosperm) had greater protein and lipid absorbance while the inner kernel (floury endosperm) had stronger starch absorbance. Pearson’s correlation analyses between FTIR peak intensities and protein/starch content showed that starch content did not have a significant correlation with infrared peaks, whereas the amide I peak at 1652 cm−1 (C=O stretching group), highly correlated with protein content (P ≤ 0.05). A calibration curve (Y = 127.79X-14.345, R2 = 0.9454) was built using peak height at 1652 cm−1 to predict protein content and this was applied to determining protein digestibility. Keywords Sorghum . Chemical compositions . FTIR spectroscopy . Protein
Abbreviations FTIR Fourier-transform infrared spectroscopy ATR Attenuated total reflection DA Discrimination analysis SEM Scan electron microscopy IVPD In vitro protein digestibility
Introduction Sorghum grain (Sorghum bicolor) is cultivated in tropical and subtropical regions around the world and is the fifth largest crop based on production. Sorghum is widely grown in the * S. R. Bean [email protected] 1
USDA, Agricultural Research Service, Center for Grain and Animal Health Research, 1515 College Ave, Manhattan, KS 66502, USA
2
Department of Agronomy, Kansas State University, Manhattan, KS 66506, USA
Great Plains area of the USA and is used in food, animal feed, and biofuel industries. Worldwide, sorghum plays an important role in food security especially in Africa and Asia because of greater drought resistance than maize or wheat (Klopfenstein and Hoseney 1995). Sorghum flour is safe as an
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