Location: Grain Quality and Structure Research
2023 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 third 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” were conducted. Collaborative research with scientists at Texas Tech University investigated the effect of nitrogen fertilization on grain protein content, protein digestibility and amino acid content of sorghum grown in three environments. Research related specifically to Sub-objective 1.A. was continued through fermentation of sorghum to produce beverages and evaluating how fermentation impacted digestibility of fermentation residues. Research also investigated protein content and digestibility after hydrolysis and ethanol fermentation of sorghum using granular starch hydrolyzing enzymes. Hydrolysis of starch resulting in fermentation residues with increased protein content and increased protein digestibility of non-tannin samples were tested. Decortication of sorghum grain effectively increased protein content and a combination of decortication and starch hydrolysis via granular enzymes could be used to produce sorghum protein isolates with improved digestibility. Research on nixtamalization and masa production from sorghum was initiated for production of sorghum tortillas. Since sorghum is increasingly used as human food, collaborative research with ARS scientists in Manhattan, Kansas, was begun to understand relationships between sorghum grain structure/composition and resistance to stored product insects. Related to Sub-objective 1.C., research was conducted to develop a new high throughput polyphenol extraction method to maximize the yield of 3-deoxyanthocyanidins and other flavonoids. Historically, acidified solvents have been used to extract 3-deoxyanthocyanidins, but certain high throughput systems do not allow the use of acids. Collaborative research with researchers at Kansas State University found that using small amounts of acid post high-throughput extraction maximized the identification and quantification of 3-deoxyanthocyanidins. This will lead to environmentally friendly extraction methods because significantly smaller amounts of corrosive acids need to be used to extract target molecules from large samples. Additionally, the effects of varying pH on sorghum polyphenols were evaluated during wet cooking. It was demonstrated that shorter cooking times and lower pH were associated with higher extractable polyphenols and higher bioactivity in the extracts. This finding will form the basis for more robust research looking into sorghum processing methods with a focus on polyphenols and bioactivity.
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. Near-infrared spectroscopy calibration curves were maintained and improved for protein content, starch content, amylose content, lysine content, crude fat, as well as improvement in discrimination models for presence or absence of tannin in sorghum. Additionally, calibration curves were developed for total phenolic content and a preliminary calibration curve for in-vitro pepsin digestibility has been developed. Collaborative research with other ARS scientists at Manhattan, Kansas, resulted in development of a single kernel near-infrared sorting instrument capable of analyzing sorghum grain. Related to development of single kernel sorting instruments, methods were modified to analyze protein content in single sorghum grains. Additionally, a collaborative project with ARS scientists in Lubbock, Texas, was initiated to develop near-infrared calibrations for analyzing dhurrin levels in sorghum plant tissues using a handheld near-infrared spectrometer. Additional collaborative research with other ARS at Manhattan, Kansas, developed automated methods for analyzing images of sorghum grain to measure grain structure.
Accomplishments
1. Protocol for accurately analyzing protein in single grains using nitrogen combustion. The ability to screen sorghum grain samples and sort those individual grains based on protein content would speed up the process of developing new sorghum lines. To support the development of instruments that can accomplish single grain sorting, a reference method for analyzing protein in single grains was needed. ARS scientists in Manhattan, Kansas, developed a calibration curve to measure protein using commercial nitrogen analyzers. This procedure has enabled research to develop single grain sorting instruments. Sorghum breeders are interested in the ability to sort single sorghum grains, and this would reduce the time and cost of breeding new sorghum lines with improved protein content.
2. Method for producing nanoparticles from sorghum bran. ARS researchers in Manhattan, Kansas, successfully made nanoparticles from sorghum bran (the outer layers of the grain). Nanoparticles made from sorghum bran were high in phenolic content. Phenolic compounds are increasingly recognized as important for human health. Because of the high phenolic content, sorghum bran nanoparticles could have application in the biomedical field for uses such as nanomedicine for disease treatment. Sorghum bran is a byproduct of sorghum milling and its use in nanoparticle production would benefit the sorghum industry by providing high value use for a byproduct. The use of bran also is an environmentally friendly source of material for production of nanoparticles, thus benefiting companies interested in nanoparticle production.
3. Effect of nitrogen fertilizer on nutritional quality of sorghum grain. There is increasing interest in the development and marketing of sorghum grain with increased protein content. To support this interest, ARS researchers in Manhattan, Kansas, collaboration with scientists from Texas Tech University in Lubbock, Texas, determined the effect of nitrogen fertilization levels and application time on sorghum grain protein content, protein digestibility, and amino acid content. All fertilizer levels increased grain protein content but had no effect on protein digestibility. As a percentage of total protein, some amino acids were found to increase as protein increased, but others decreased. Since total protein increased under fertilization but protein digestibility remained the same, fertilization of sorghum could be one avenue to increase bioavailability of protein in the grain. This research provides information to sorghum producers and food companies interested in the use of sorghum grain with increased protein content. Development of high protein sorghum grain also provides new market opportunities for the U.S. sorghum industry.
Review Publications
Cao, X., Li, N., Qi, G., Sun, X., Bean, S.R., Tilley, M., Aramouni, F.M., Wang, D. 2022. Optimization of gum isolation and protein extraction from Camelina (Camelina sativa L. Crantz) seeds using decortication. Journal of Agriculture and Food Research. 6. Article 100223. https://doi.org/10.1016/j.jafr.2021.100223.
Kessler-Mathieu, M.S., Tilley, M., Prakash, S.R., Bean, S.R., Peiris, K.H., Aramouni, F.M. 2023. TaqMan-based duplex real-time PCR approach for analysis of grain composition (Zea mays - Sorghum bicolor) in feedstock flour mixes for bioethanol production. ACS Agricultural Science and Technology. 3(2):232–240. https://doi.org/10.1021/acsagscitech.2c00314.
Somayanda, I.S., Bean, S.R., Ioerger, B.P., Hayes, C.M., Emendack, Y., Jagadish, K.S. 2023. Comparative assessment of grain quality in tannin versus non-tannin sorghums in the sorghum association panel. Cereal Chemistry. 100(3):663-674. https://doi.org/10.1002/cche.10643.
Yoganandan, M., Buenavista, R.M., Bean, S.R., Aramouni, F.M., Dogan, H., Siliveru, K. 2022. Influence of tempering methods on waxy white sorghum kernel, milling, and flour properties. Biosystems Engineering. https://doi.org/10.13031/ja.15221.
Akin, P.A., Demirkesen, I., Bean, S.R., Aramouni, F.M., Boyaci, I.K. 2022. Traditional and novel sorghum-based bread products – A literature review. Foods. 11. Article 2466. https://doi.org/10.3390/foods11162466.
Ayalew, H., Peiris, K.H., Chiluwal, A., Kumar, R., Tiwari, M., Ostmeyer, T., Bean, S.R. 2022. Genetic control of sorghum [Sorghum bicolor (L.) Moench] grain quality under variable environments. The Plant Genome. 15. Article e20227. https://doi.org/10.1002/tpg2.20227.
Santana, A.L., Peterson, J.M., Perumal, R., Hu, C., Sang, S., Siliveru, K., Smolensky, D. 2023. Post acid treatment on pressurized liquid extracts of sorghum bicolor grain and plant material improves quantification and identification of 3-deoxyanthocyanidins. Processes. https://doi.org/10.3390/pr11072079.
