Location: Grain Quality and Structure Research2012 Annual Report
1a. Objectives (from AD-416):
The long term objective is to increase sorghum grain utilization by identifying the physical and biochemical components important for food, feed, and bio-industrial quality. Over the next 5 years, the following specific objectives will be addressed: Objective 1: Identify optimum kernel characteristics for processing of sorghum. Objective 2: Determine role of starch, proteins, phenolic compounds and their interactions in digestibility and functional quality of sorghum. • Sub-objective 2.A. Determine the molecular basis for protein cross-linking in sorghum and its impact on functionality and digestibility of sorghum. • Sub-objective 2.B. Determine the relationships between starch content, composition and granule size on functionality and digestibility of sorghum. • Sub-objective 2.C. Ascertain the interactions between and among sorghum phenolic compounds, protein and starch. • Sub-objective 2.D. Determine how physical and biochemical properties of the kernel influence mold resistance and are related to processing quality. Objective 3: Determine the impact of the environment on sorghum kernel structure and composition as well as their relationship to end use quality. Objective 4: Develop biochemical and physical markers to predict end-use quality of sorghum grain for food and feed uses.
1b. Approach (from AD-416):
Objective 1 addresses the relationships among physical grain structure, roller milling, and flour quality for the manufacture of wheat-free sorghum food products. Objectives 2a and 2b further investigate sorghum flour quality by addressing the functional and nutritional role of protein and starch in end-use quality of sorghum. Objective 2c is intertwined with Objectives 1, 2a, and 2b by studying the interaction among phenolic acids, proteins and starch. Objective 2d combines key factors from Objectives 1, 2a, 2b, and 2c through the impact of grain hardness, proteins, and phenolic compounds on mold resistance. Not only do these components play a role in mold resistance, but damage to sorghum grain by mold alters hardness (thus milling and flour quality, Objective 1), biochemical properties of sorghum (thus functionality, Objective 2a, b, and c). Objective 3 aims to better understand the process of grain development in sorghum which provides supporting information for the primary Objectives 1 and 2. Objective 4 is also a supportive objective geared towards providing “tools” to assist in achieving Objectives 1-3. This project addresses processing of sorghum into flour, describes how the biochemical components of the flour affect the functional and nutritional quality of the flour and how mold resistance also influences grain and flour quality.
3. Progress Report:
Screening of a large (over 300 samples) genetically diverse sorghum germplasm collection for protein content, in vitro protein digestibility, starch granule size distribution, total phenolic content, and anti-oxidant levels was completed. Starch gelatinization properties of a subset of this collection were measured. Additional subsets of sorghum samples from the collection that varied in protein digestibility, physical grain traits, and phenolic content were selected and are currently being grown by collaborators at Kansas State University for future research. Additionally, physical grain traits, protein digestibility, and phenolic content were measured on a collection of sorghum samples with known genetic differences controlling the development of the outer layers of the sorghum grain. Sorghum samples from this population were analyzed in both normal grain and in grain that had been infected with mold species known to naturally occur in sorghum to better understand grain weathering and its effects on grain quality in sorghum. Physical grain traits, protein digestibility, and phenolic content were also measured for a collection of sorghum lines being evaluated for cold tolerance in order to determine what grain traits may be correlated with cold tolerance. Research was also completed that demonstrated that sorghum flour with a wide range of particle sizes could be produced using laboratory mills without significantly changing starch damage levels. A wheat-free sorghum bread formula using whole grain sorghum flour and high levels of tannin containing sorghum bran was developed which significantly increased the fiber content and anti-oxidant levels of the bread without impacting bread quality or sensory attributes of the bread. Research using various proteases to digest isolated sorghum proteins was conducted and some digested sorghum proteins were found to have properties similar to egg whites, which could provide a new avenue for improving the functionality of sorghum proteins in food systems.
1. Screening of a genetically diverse sorghum associating mapping panel. Compared to grains such as wheat and corn, sorghum has had little research conducted on relationships between genetics, grain traits and end-use quality. Sorghum has also not been traditionally bred for specific end-use quality traits. To begin to address these issues ARS researchers at Manhattan, Kansas completed screening of a large (over 300 samples) genetically diverse sorghum population for grain composition and important end-use quality traits such as protein digestibility, starch granule size distribution and anti-oxidant levels. This information will provide sorghum breeders and geneticists the ability to select sorghum germplasm with improved quality and identify key genes related to end-use quality in sorghum.
2. High anti-oxidant high fiber wheat-free sorghum bread formula. Wheat-free foods often contain high levels of purified starches and refined flour which limits their nutritional properties. To improve the nutritional profile of wheat-free sorghum bread, ARS researchers at Manhattan, Kansas developed a sorghum bread formula containing whole sorghum flour plus added sorghum bran that contained high levels of tannin. Bran is high in fiber and tannins are known to be potent anti-oxidants, thus this formula resulted in bread with high levels of dietary fiber and anti-oxidants. This work is important because individuals with different forms of gluten intolerances often comprise nutritional benefits (i.e. foods that lack fiber and other health promoting compounds) for pure calories. This research shows that nutritionally dense sorghum bread that is safe for individuals with gluten intolerance can be formulated and processed.
3. Production of sorghum flour with a range of particle sizes with constant starch damage. Changing the particle size of flour has a direct impact on the functional properties of that flour. Flour particle size influences factors such as water uptake, product texture, and mouth feel. Typically, producing flours that vary in particle size also results in changing the starch damage of the flours. Starch damage also changes the functionality of flour, making it difficult to determine what effect flour particle size has on flour quality independent of starch damage levels. ARS researchers in Manhattan, Kansas used a laboratory ball mill to create sorghum flour that varied in particle size but had little change in starch damage levels. This will allow the researchers to independently research the effect of particle size and starch damage on sorghum flour quality and identify the optimum levels of each for producing high quality sorghum bread.
Bean, S., Ioerger, B.P., Smith, B.M., Blackwell, D.L. 2012. Sorghum protein structure and chemistry. In: Awika, J., Piironen, V. and Bean, S. R. editors. Advances in Cereal Science: Implications to Food Processing and Health Promotion (ACS Symposium). 2nd edition. Washington, D.C.: American Chemical Society. p. 131-148.