Research Project: Impact of the Environment on Sorghum Grain Composition and Quality Traits

Location: Grain Quality and Structure Research

2019 Annual Report

Objectives
Objective 1: Integrate commercial grain sorghum quality traits with the timing and duration of heat and/or drought stress during grain fill. • Sub-Objective 1.A. Determine how timing of drought stress during grain fill impacts protein and starch chemistry and digestibility. • Sub-Objective 1.B. Determine the degree to which heat stress impacts sorghum grain quality traits. Objective 2: Enable new rapid/high-throughput commercial methods to measure grain sorghum composition and quality traits. • Sub-Objective 2.A. Develop an in-vitro cellular antioxidant activity assay for measuring the efficacy of sorghum bioactive compounds in response to radical oxidative species. • Sub-Objective 2.B. Determine the effectiveness of a blood glucometer in determining fermentation efficiency using sorghum grain. Objective 3: Integrate the stability/variability of grain sorghum compositional quality and bionutrient components across multiple commercial production environments. • Sub-Objective 3.A. Evaluate the variability in sorghum grain composition related to protein and starch across multiple growing environments. • Sub-Objective 3.B. Characterize phytonutrient composition in tannin and black sorghum germplasm grown at multiple locations. Objective 4: Molecular biological technologies will employ gene flow analysis to identify sorghum compositional and quality traits variants migrating through field/commercial sorghum breeding programs.

Approach
Sorghum [Sorghum bicolor (L.) Moench] is an important drought tolerant crop in regions of the Great Plains where water is limited and rainfall unpredictable. Sorghum has been primarily used for animal feed in the U.S. but recently has seen increasing use in the food and biofuel industries which has provided a new growth area for sorghum utilization. That said, there has not been extensive research conducted on grain quality factors related to sorghum. Recent advances have been made regarding improving sorghum protein and starch digestibility at the genetic level, yet little is known about how environmental factors impact sorghum grain quality attributes and nutritional bioavailability. Sorghum is typically grown under non-irrigated conditions and can face serious drought and heat stress during grain fill. Drought and heat stress may become more prevalent in sorghum growing regions due to climate change and have the potential to severely impact sorghum grain composition and end-use quality traits. Consistency is an important quality attribute of cereal crops and further research is required to quantify the degree to which sorghum grain quality is impacted by the environment. Our research will support on-going efforts to improve sorghum grain quality at the genetic level by providing grain quality information to breeding programs about the stability of various traits. We will provide knowledge of how drought and heat stress impacts sorghum grain quality, ultimately providing information necessary for the sorghum breeding community to improve the end-use quality of sorghum.

Progress Report
The overall goal of this project is to evaluate the impact of environment on sorghum grain quality and composition, particularly the effect of heat and drought stress. The project is completing the fourth year of its current 5-year plan. Progress this year includes finalizing manuscripts related to Objective 1: Integrate commercial grain sorghum quality traits with the timing and duration of heat and/or drought stress during grain fill. A peer reviewed manuscript on research that analyzed sorghum grain composition grown under heat and drought stress has been finished and published, this research identified sorghum lines that maintained their end-use quality under stress better than other lines tested and are therefore valuable for use in sorghum breeding programs. A second manuscript directly comparing performance of corn and sorghum germinated under cold temperatures and how grain traits influenced cold-tolerance was published. Related to Objective 2: Enable new rapid/high-throughput commercial methods to measure grain sorghum composition and quality traits, work on developing NIR curves for predicting basic sorghum grain composition was continued with preliminary research on developing NIR calibration curves for determining sorghum grain amino acid composition conducted. Preliminary findings suggest that NIR will accurately determine the levels of several amino acids important to the feed industry. This will help in screening germplasm for improved nutritional quality. Research on developing an NIR method to determine the composition of corn-sorghum flour mixtures was finished with the final calibration model able to determine the amount of sorghum in corn-sorghum mixtures with an r-square value of 0.977 and a standard error of prediction of about 5 percent. A sorghum bioenergy company is in the process of adopting this methodology for use in an ethanol plant. Research to develop a real-time PCR method to serve as validation for the NIR methodology has continued with preliminary research showing the method to achieve detection limits as low as 1% sorghum flour in experimental mixtures of corn and sorghum flour. Related to Objective 3: Integrate the stability/variability of grain sorghum compositional quality and bionutrient components across multiple production environments, extracts from high polyphenol sorghum lines were evaluated for their ability to prevent cancer development in human colon cancer cells. Experiments supporting the primary project objectives above were also conducted to evaluate grain vitreousity in sorghum in order to expand our understanding of how grain physical structure is related to grain composition. Approximately 200 sorghum lines from a cold tolerant sorghum panel were screened for grain hardness and kernel size as well as for the presence of tannins. This research was done in collaboration with scientists from Kansas State University and supports the development of cold-tolerant germplasm. Collaborative research projects were also started to investigate how damage from stored insect pests impacts phenolic content and composition and how cooking impacts the bioactivity of sorghum phenolic compounds.

Accomplishments
1. Colon cancer preventative effect of high phenolic sorghum bran. Sorghum grain is known to contain high levels of phenolic compounds that may play a role in preventing cancer. However, exactly how sorghum phenolic compounds may help prevent cancer is not known. To further understand the potential anti-cancer properties of sorghum phenolic compounds, ARS scientists in Manhattan, Kansas, treated human colon cancer cells with different doses of extracts from a sorghum line previously found to contain very high levels of phenolic compounds. Cancer growth was reduced in the cell lines treated with the sorghum phenolic extracts. Furthermore, treatment of the cancer cell lines with sorghum phenolic extracts was found to alter regulation of specific genes important in cancer development. This study provides information on how sorghum phenolics may help prevent colon cancer. This research also shows the benefits of developing sorghum germplasm with increased levels of phenolic compounds to increase the value and utilization of grain sorghum.

2. Method to determine the composition of sorghum-corn flour mixtures. In some situations, bioethanol plants may use mixed feed stocks of both sorghum and corn grain. To optimize efficiency of ethanol plants and marketing of the resultant ethanol, it is beneficial to be able to determine the composition of mixed feedstocks being used when it is not possible to physically keep feedstocks separated. To address this issue, ARS scientists in Manhattan, Kansas, collaborated with a commercial ethanol plant, scientists and personnel from Kansas State University and the Center for Sorghum Improvement in Manhattan, Kansas, to develop a near-infrared spectroscopy (NIRS) method to determine the composition of sorghum-corn flour mixtures. The NIRS method was able to accurately determine the percentage of sorghum in such mixtures within plus or minus 5 percent. This methodology will help the ethanol plants using mixed feed stocks optimize plant performance and identify markets for ethanol made from specific feed stock mixtures.

3. Isolation of sorghum proteins for use in food systems. Sorghum proteins have unique properties that have not been widely explored for use as food additives. To support the use of sorghum protein isolates in foods, ARS scientists in Manhattan, Kansas, in collaboration with scientists from Italy (from the Istituto di Bioscienze e BioRisorse, the University of Salento and the CNR-Institute of Biosciences and Bioresources) compared five different extraction procedures for isolating sorghum proteins from flour. Each extraction procedure produced sorghum protein isolates with differences protein composition and purity. Molecular weight distribution did not vary widely among the extraction methods tested, but surface hydrophobicity did. These results showed that proteins could be isolated from sorghum flour that may have different functionality in food systems. This research supports the development of isolated sorghum proteins for use as food additives, providing new markets, utilization and value for sorghum grain.

Review Publications
Peiris, K., Bean, S.R., Chiluwal, A., Perumal, R., Jagadish, K. 2019. Moisture effects on robustness of sorghum grain protein NIR spectroscopy calibration. Cereal Chemistry. 96: 678-688. https://doi.org/10.1002/cche.10164.
Somayanda, I., Perumal, R., Bean, S.R., Sunoi, J., Jagadish, K. 2019. Water deficit and heat stress induced alterations in grain physico-chemical characteristics and micronutrient composition in field grown grain sorghum. Journal of Cereal Science. 86:124-131. https://doi.org/10.1016/j.jcs.2019.01.013.
Tesso, T.T., Gobena, D.D., Perumal, R., Bean, S.R., Wilson, J.D., Little, C. 2019. Registration of seventeen acetolactate synthase-inhibitor herbicide resistant sorghum pollinator lines. Journal of Plant Registrations. 13:212-216. https://doi.org/10.3198/jpr2018.05.0032crg.
Perumal, R., Tesso, T., Kofoid, K.D., Aiken, R.M., Prasad, V., Bean, S.R., Wilson, J.D., Herald, T.J., Little, C.R. 2018. Registration of six grain sorghum pollinator (R) lines. Journal of Plant Registrations. 13:113-117. https://doi.org/10.3198/jpr2017.12.0087crp.
Duressa, D., Weerasooriya, D., Bean, S.R., Tilley, M., Tesso, T. 2018. Review of genetic basis of protein digestibility in Grain sorghum. Crop Science. 58:2183-2199. https://doi.org/10.2135/cropsci2018.01.0038.
Cox, S.R., Noronha, L.E., Herald, T.J., Bean, S.R., Lee, S., Perumal, R., Smolensky, D. 2019. Optimization of ethanol-based extraction conditions of sorghum bran bioactive compounds with downstream anticancer properties. Heliyon. https://doi.org/10.1016/j.heliyon.2019.e01589.
Antony, R., Kirkham, M., Todd, T., Bean, S.R., Wilson, J.D., Armstrong, P.R., Maghirang, E.B., Brabec, D.L. 2019. Low-temperature tolerance of maize and sorghum seedlings grown under the same environmental conditions. Journal of Crop Improvement. 33(3):287-305. https://doi.org/10.1080/15427528.2019.1579139.
Weerasooriya, D.K., Bean, S.R., Nugusu, Y., Ioerger, B.P., Tesso, T.T. 2018. The effect of genotype and traditional food processing methods on in-vitro protein digestibility and micronutrient profile of sorghum cooked products. PLoS One. 13(9):e0203005. https://doi.org/10.1371/journal.pone.0203005.