Soy protein has been the most widely researched protein-based adhesive; however, soy protein remains an expensive product because of its competitive uses in both food and feed industries. To mitigate such competition, this project was aimed to investigate protein composites by mixing low value sorghum and canola proteins into soy proteins. In addition to cost reduction, a novel composite with optimal composition of three protein were identified showing superior adhesion properties. For example, compared to soy protein alone, the optimum protein mixture (sorghum:canola:soy = 3:2:5) had a 63 % increase in dry adhesion strength, 103 % increase in wet adhesion strength, and 61 % increase in soaked adhesion strength. The physiochemical properties of different protein samples were characterized using rheometry, Fourier transform infrared spectroscopy, size exclusion chromatography, SDS-PAGE and surface hydrophobicity analysis. Protein analysis showed that the improved adhesive performance was likely due to optimizing protein molecular weight distribution and hydrophobicity. The present study demonstrates a simple, straight forward approach to improve soy protein-based adhesion performance and also reduce the overall cost of the plant protein-based composites as adhesives.

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.

A white low polyphenol sorghum, a red-waxy starch sorghum, a red-tannin sorghum with moderate polyphenol levels, and a red non-tannin sorghum were evaluated for susceptibility to Rhyzopertha dominica (Fab.) (Coleopter: Bostrychidae), the lesser grain borer. Density levels of 0 (untreated controls), 10, 20, or 30 mixed-sex adults were exposed on 100 g replicates of each of the varieties and removed after two weeks. Progeny production and physical damage were evaluated on each variety, along with quality characteristics such as moisture content, protein, starch, phenolic content, and kernel vitreousity. Progeny production and physical damage varied with density level and variety, but was generally lowest on the red-waxy sorghum. At the density level of 30 parental adults more progeny were found in the red-tannin sorghum compared to the other varieties. Starch content, kernel vitreousity and hardness was lower in the red-tannin sorghum. Total phenolic content was 2-3x greater in the red-tannin sorghum compared to the other varieties, but the high phenolic content did not seem to affect R. dominica progeny production. Results suggest the insects bypassed the bran layer of the sorghum varieties to feed on the germ and endosperm. Results of this study could be used to further explore the relationships between kernel hardness, chemical composition, and susceptibility to stored product insects, and incorporate results into management programs for maintaining quality of stored sorghum and processed sorghum food by-products. Published by Elsevier Ltd.

A method for fractionating sorghum proteins using extraction solvents and techniques designed to obtain polymeric protein structures (especially disulfide linked) was developed. Extraction and separation conditions were optimized in terms of completeness of protein extraction, sample stability, and analytical resolution. After pre-extraction of albumins and globulins, a 3-step sequential procedure involving no reducing agents was applied to ground whole sorghum flour. The three fractions obtained represented proportionally different protein polymer contents and molecular weight distribution as evidenced by comparative size exclusion chromatography. Protein composition also varied among the extracts with differences in kafirin composition and non-kafirin proteins detected in the fractions by RP-HPLC and SDS-PAGE analysis. The ability to quantify and further characterize sorghum polymeric protein complexes will be useful for additional studies linking protein structures with functionality and digestibility and variations for these properties within diverse sorghum germplasm.