Location: Grain Quality and Structure Research
2024 Annual Report
Objectives
OBJECTIVE 1: Determine and quantify grain components linked to ‘health-promoting’ benefits and commercial quality of sorghum foods and feed.
• Subobjective 1.A. Determine the mechanism related to the reduced protein quality of cooked sorghum flour.
• Subobjective 1.B. Characterize protease inhibitors in sorghum and their role in modulating digestibility in sorghum flour.
• Subobjective 1.C. Evaluate and identify bioactive compounds in sorghum linked to anti-cancer and other health promoting properties.
OBJECTIVE 2: Develop and improve methodologies for rapid prediction and measurement of sorghum grain attributes linked to valuable end-use quality traits.
• Subobjective 2.A. Utilize UHPLC (ultra-high-performance liquid chromatography) size exclusion for characterizing sorghum polymeric protein complexes related to end-use quality of sorghum.
• Subobjective 2.B. Develop near infrared spectroscopic methods to predict grain composition and quality traits of sorghum.
Approach
Sorghum is an important drought tolerant crop in the central U.S. where water is limited and rainfall unpredictable. Sorghum has been primarily used for animal feed in the U.S. and is consistently used by the biofuel industry and increasingly used in human foods. As for any cereal, grain composition plays an important role in its utilization. To support utilization of sorghum grain, research is needed that identifies grain components linked to functional and nutritional quality of sorghum products. One issue for sorghum utilization is how processing, especially cooking, impacts sorghum flour nutritional and functional properties. It is known that heating increases sorghum protein cross-linking, which in turn affects both protein and starch functionality and digestibility. The exact mechanism of how this occurs is not known; nor is it known how protein and starch changes influence the role of digestive inhibitory compounds in sorghum. Identifying the mechanism behind these changes will provide avenues to improve sorghum flour quality as well as provide new targets to improve sorghum grain composition at the genetic level. Likewise, sorghum is known to have high levels of bioactive compounds that have potential human-health promoting benefits. However, much of the past research on bioactive compounds in sorghum has been based on chemical assays. To further define and identify the health-promoting benefits of sorghum, research using additional methods such as cellular based assays are needed. Such research will help define the value of sorghum in human foods and provide targets for the genetic improvement of sorghum.
Progress Report
The overall goal of this project is to identify grain composition traits related to end-use quality and value of sorghum. The project is completing the fourth year of its current 5-year plan. Progress this year includes several research projects related to the overall goal of Objective 1 - “Determine and quantify grain components linked to health-promoting benefits and commercial quality of sorghum foods and feed.” Collaborative research with scientists at Texas Tech University and the University of Nevada, Reno, investigated protein and starch content and composition of sorghum lines during grain fill to help identify crucial timepoints in the development of sorghum grain and genes associated with protein and starch content. Research was also conducted in collaboration with Texas Tech University to investigate changes to sorghum protein content and composition in a chemically induced mutant population of sorghum. Analysis of grain samples by NIRS (near-infrared spectroscopy) was initiated to support a large, multi-location project in collaboration with Texas A&M University, Kansas State University, and ARS-Lubbock, Texas. Grain samples were also analyzed by NIRS to support collaborative research with the University of Nevada, Reno. In total, approximately 5,500 samples have been analyzed by NIRS to support various collaborative research projects aimed at improving sorghum grain composition and end-use quality. Collaborative research with Kansas State University on characterizing the physical and proximate composition of a large-seeded sorghum population was completed and research is in progress analyzing protein composition in this population. Research on nixtamalization and masa production from sorghum was continued and waxy sorghum lines were evaluated for production of sorghum tortillas. The effect of extraction methods on the compositional and structural characteristics of sorghum oleoresins as a value-added component of sorghum grain were conducted in collaboration with researchers at Kansas State University. Collaborative research with Kansas State University was also completed on comparing methods for measuring amylose content in sorghum flour and collaborative research was started on functionality of waxy sorghum starch and sorghum flour. Research with Kansas State University was also completed on the use of alternative tempering methods to improve milling of sorghum grain and milling procedures to produce high protein sorghum flour. Research on feeding fermented tea to pigs was conducted in collaboration with scientists at Kansas State University to evaluate potential health effects of the fermented tea. Collaborative research with other ARS scientists in Manhattan, Kansas, was continued to understand relationships between sorghum grain physical properties and protein content and resistance to stored product insects. Progress was also made on the development of a novel method to separate polyphenolic compounds based on degree of polymerization. This methodology is an important step in characterizing the bioactivity of sorghum tannins and oligomeric polyphenols, which will lead to better breeding of sorghum lines as a functional food. In addition, the polyphenol expression profile in leaf samples was evaluated on five sorghum genotypes across the growing season. Research was also conducted to make in-depth comparison of polyphenols in three popular gluten free grains, sorghum, corn and rice, using commercially available high phenolic genotypes.
Research related to Objective 2 – “Develop and improve methods for rapid prediction and measurement of sorghum grain attributes linked to valuable end-use quality traits” was continued. To improve and maintain existing near-infrared (NIR) spectroscopy calibration curves, samples were identified for wet chemistry analysis for total protein, total starch, amylose content, and fat. Data from the wet chemistry analysis was then incorporated back into existing calibrations. Research was also begun to develop a calibration curve to predict ash content in whole sorghum grain. To support the development of single kernel NIR calibrations, research was begun to determine optimum solvents to extract starch from single ground sorghum grains. The optimized solvent system should allow for both total starch and amylose content to be measured from one sorghum grain. Research was initiated to optimize a commercial instrument for high-speed imaging of single sorghum kernels. Initial calibration of the instrument was completed for recognizing sorghum kernels with a wide range of color and size. Research to build models to identify broken kernels and kernels with glumes attached was begun. Likewise, collaborative research with ARS-Manhattan scientists was started to build models for the instrument to identify insect damaged kernels. Research was also initiated to use bulk density measurements to determine grain vitreosity and research to automate image analysis of sorghum grain for determining vitreosity and endosperm color was continued in collaboration with other scientists at ARS-Manhattan.
Accomplishments
1. Determined changes to sorghum polyphenols cooked at high moisture and different pH levels. Sorghum is known to contain high levels of compounds called polyphenols that have important human health benefits, including anti-cancer activity and reducing inflammation. However, sorghum is generally cooked prior to human consumption. Limited research has been done to show how sorghum polyphenols change when cooked. This research by ARS researchers in Manhattan, Kansas, used a model system of cooking sorghum at different pH’s to determine how the properties of polyphenols might change when cooked. Cooking time and pH both impacted sorghum polyphenol levels and activity. This study will help guide future research on sorghum polyphenols in foods and provide valuable information related to production of sorghum foods for improving human health.
2. Comparison of methods for measuring amylose content in sorghum. There is increasing interest in the development and use of low amylose (referred to as waxy) sorghum grain. Flour made from waxy sorghum grain may have unique properties making it a valuable food ingredient. Waxy sorghum grain also has higher fermentation efficiency than non-waxy sorghum grain and could have benefits in the ethanol industry. However, there are no standard methods for measuring amylose content in grains, which results in confusion when different methods are used. To improve the measurement of amylose content in sorghum, ARS researchers in Manhattan, Kansas, and collaborators at Kansas State University, conducted thorough research on comparing methods of measuring amylose content in sorghum. Three commonly used methods were found to produce comparable results. These methods could be used in research and in measuring amylose in commercial sorghum grain channels and provide consistent results. This information will benefit sorghum researchers, seed companies, and food companies interested in the use of waxy sorghum.
3. Sorghum starch hydrolysis with granular starch hydrolyzing enzymes and impact on protein digestibility. It is well known that the protein digestibility of sorghum decreases when sorghum is cooked. During the production of ethanol, sorghum is cooked at high temperatures which results in a decrease in the protein digestibility of the residue after ethanol production. The residue left after fermentation is a valuable co-product for the ethanol industry as an animal feed. To improve the quality of this co-product, ARS researchers in Manhattan, Kansas, tested the use of a type of enzyme to digest starch that does not require high temperatures to be used, as is traditionally done during ethanol production. Using the granular starch enzymes resulted in increased protein digestibility of the residues left after starch hydrolysis. This research demonstrates that granular enzymes could be used in the ethanol industry and improve the quality of the residues left after fermentation and thus produce a higher value co-product. Residues left after starch digestion could also be used as protein isolates in food products and plant-based protein applications.
4. Evaluating properties of large-seeded sorghum lines. Sorghum has a small grain which can be difficult to process for some industries such as in cattle feeding operations. Increasing the size of sorghum grain may help improve the use of sorghum in these situations. ARS researchers in Manhattan, Kansas, measured the physical and chemical properties of a large-seeded sorghum population grown by collaborators at Kansas State University. Grain size in the large-seeded population was two times greater than the average of a diverse set of sorghum with normal-sized grains, and some large-seeded varieties were almost three times larger. On average, the large-seeded sorghum population had higher protein than average levels of normal-sized sorghum used for comparison. Future research is still needed to evaluate the large-seeded sorghum over more locations to verify the increased protein levels. These results show that sorghum lines with larger seeds and with potentially higher protein content could be developed and would benefit industries where the small size of sorghum grain limits its potential use.
5. Ultrasound tempering of sorghum grain. Interest in sorghum for food use has been steadily increasing in the U.S. A major use of sorghum in foods is in bakery products, especially for the gluten-free food market. To be used in the baking industry, sorghum grain must first be milled into flour. Before milling, moisture is added to grain to temper the outer layers and facilitate the separation of the inner (endosperm) and outer layers (bran) of the grain. ARS researchers in Manhattan, Kansas, in collaboration with scientists at Kansas State University, investigated the use of ultrasound during the tempering of sorghum before milling. Ultrasound tempering (UST) was found to improve milling yield and impacted flour properties such as particle size and level of bran in the flour. UST offers a new method of improving sorghum milling quality which would benefit companies interested in using sorghum flour in food products.
Review Publications
Ostmeyer, T.J., Somayanda, I.S., Peiris, K.H., Bean, S.R., Ritchie, G., Jagadish, K. 2024. Grain protein and amino acid dynamics in sorghum with in-season split-nitrogen application. Cereal Chemistry. https://doi.org/10.1002/cche.10783
Pulivarthi, M.K., Buenavista, R.M., Bangar, S.P., Pordesimo, L.O., Bean, S.R., Silveru, K. 2023. Dry fractionation process operations in the production of protein concentrates: A review. Trends in Food Science and Technology. 22(6):4670-4697. https://doi.org/10.1111/1541-4337.13237.
Peiris, K.H., Bean, S.R., Wu, X., Sexton-Bowser, S., Tesso, T. 2023. Performance of a handheld Micro NIR instrument in comparison with laboratory benchtop NIR instrument for determining protein levels in harvested sorghum grain samples. Foods. https://doi.org/10.3390/foods12163101.
Kaya, E.C., Yucel, U., Peiris, K.H., Aramouni, F.M. 2023. Sorghum Oleoresins: Effect of extraction on compositional and structural characteristics. Journal of the American Oil Chemists' Society. https://doi.org/10.1002/aocs.12748.
Pruett, A., Aramouni, F.M., Bean, S.R., Haub, M. 2023. Effect of flour particle size on the glycemic index of muffins made from whole sorghum and comparison to muffins made from whole corn, brown rice, whole wheat, or refined wheat flours. Foods. https://doi.org/10.3390/foods12234188
Ostmeyer, T.J., Somayanda, I.S., Bean, S.R., Dhillon, R., Hayes, C.M., Ritchie, G., Asebedo, A.R., Emendack, Y., Jagadish, K.S. 2023. Impact of in-season split application of nitrogen on intra-panicle grain dynamics, grain quality and vegetative indices that govern nitrogen use efficiency in sorghum. Plant and Soil. https://doi.org/10.1002/jpln.202200325.