Analysis of sorghum content in corn–sorghum flour bioethanol feedstock by near infrared spectroscopy

Abstract

In the sorghum-growing regions of the U.S., some bioethanol plants use mixtures of corn and sorghum grains as feedstocks depending on price and availability. For regulatory purposes and for optimizing the ethanol manufacturing process, knowledge of the grain composition of the milled feedstock is important. Thus, a near infrared spectroscopy method was developed to determine the content of sorghum in corn–sorghum flour mixtures. Commercial corn and sorghum grain samples were obtained from a bioethanol plant over an 18-month period and across two crop seasons. An array of corn–sorghum flour mixtures having 0–100% sorghum was prepared and scanned using a near infrared spectrometer in the 950–1650 nm wavelength range. A partial least squares regression model was developed to estimate sorghum content in flour mixtures. A calibration model with R2 of 0.99 and a root mean square error of cross validation of 3.91% predicted the sorghum content of an independent set of flour mixtures with r2 = 0.97, root mean square error of prediction = 5.25% and bias = −0.49%. Fourier-transform infrared spectroscopy was utilized to examine spectral differences in corn and sorghum flours. Differences in absorptions were observed at 2930, 2860, 1710, 1150, 1078, and 988 cm−1 suggesting that C–H antisymmetric and symmetric, C=O and C–O stretch vibrations of corn and sorghum flours differ. The regression coefficients of the near infrared model had major peaks around overtone and combination bands of C–H stretch and bending vibrations at 1165, 1220, and 1350 nm. Therefore, the above results confirmed that sorghum content in corn sorghum flour mixtures can be determined using near infrared spectroscopy.

TaqMan-Based Duplex Real-Time PCR Approach for Analysis of Grain Composition (Zea mays - Sorghum bicolor) in Feedstock Flour Mixes for Bioethanol Production

“…Samples of corn and sorghum grains were cleaned, visually inspected for purity, and then ground using a coffee grinder (Krups Fast Touch F203, Parispanny, NJ, USA) for 30 s and sifted using a 5/64 in. round (∼1.98 mm) commercial sieve (Seedburo, Des Plaines, IL, USA) as described previously . For validating of quantitative analyses using our duplex real-time PCR assay, binary mixtures of maize-sorghum flour ranging from 0% to 100% sorghum flour by weight in 10% increments were prepared.…”

“…round (∼1.98 mm) commercial sieve (Seedburo, Des Plaines, IL, USA) as described previously. 6 For validating of quantitative analyses using our duplex real-time PCR assay, binary mixtures of maize-sorghum flour ranging from 0% to 100% sorghum flour by weight in 10% increments were prepared. Also, ten binary mixtures with randomly assigned sorghum levels that ranged from 0% to 100% by weight were prepared.…”

“…A comparison of particle size distributions on flour blend collected from bioethanol plant and of binary mixtures prepared "in-house" for our study was previously performed using a Beckman-Coulter LS13-320 laser diffraction particle size analyzer (Beckman-Coulter Life Sciences, Indianapolis, IN, USA) to validate that the particle size was comparable. 6 Moisture content was measured in both sorghum (MC = 12.38%) and maize flours (MC = 12.68%) to ensure it was comparable.…”

“…TaqMan probe chemistry in real-time PCR produces specific fluorescent signals for the target species, which is crucial for the multiplex reactions required for the analysis of numerous species in a mixture in a single step. , Numerous TaqMan chemistries and instruments are now available for detection and multiplexing. Alternative methods using near-infrared spectroscopy, laser-induced breakdown spectroscopy, and front-face synchronous fluorescence spectroscopy have been reported for determining mixtures of cereal flours including sorghum and maize blends. The real-time PCR method reported here would make a good complement to these spectroscopic methods to validate results and be used as a reference method.…”

“…Knowing the grain composition of the milled feedstock stream would be helpful before beginning the liquefaction stage of the ground feedstock to optimize enzyme doses, and consequently the starch conversion efficiency to bioethanol. 6 In recent years, sorghum's use in the ethanol market has seen very strong growth, with around 40 percent of domestic sorghum going to bioethanol production. Sorghum has several advantages over maize and sugar cane including pricing (sorghum is typically 20 to 30 cents cheaper per bushel than maize); the use of sorghum grain in addition to maize grain allows a diversification of feedstocks for bioethanol plants which provide them more flexibility around markets/trade and price fluctuation of commodities and minimizes vulnerability in case of drought or harsh conditions of their main feedstock.…”