Location: Grain Quality and Structure Research2013 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:
Data analysis was finished for the screening of a sorghum association mapping panel, by incorporating genetic data with biochemical data. Methods for extracting and studying cross-linked sorghum protein fractions were developed. A subset of samples from the association mapping panel that varied in protein digestibility were selected for further research using this method and correlations to protein digestibility were found for the most cross-linked protein fractions. In addition, research with a visiting graduate student from Australia was done on sorghum samples with known allelic variants for the kafirin genes. This sample set was previously used to explore the relationships between sorghum protein composition and ethanol production. More detailed work on this sample set was completed this year with the water and salt soluble protein fractions. This protein based research is related to the objective “determine the molecular basis for protein cross-linking in sorghum and its impact on functional and nutritional quality of sorghum”. Research on the effect of genetics by environment on sorghum starch molecular weight distribution found that environment had an effect on sorghum starch chemistry. Methods were optimized to extract and analyze large numbers of starch samples quickly. Starch based research was conducted to meet the objective to “determine the relationships between starch content, composition and granule size on functionality and digestibility of sorghum”. Research to support the objective “ascertain the interaction between and among sorghum phenolic compounds, protein and starch” was conducted by developing high throughput methods for analyzing phenolic compounds in sorghum. Such methods are needed to measure the content of specific phenolic compounds and to determine how levels of these phenolics may influence protein digestibility. Research with scientists at the University of Nebraska, Lincoln was carried out to investigate the role phenolic compounds may play on the digestion of starch.
1. A sensitive and reproducible high throughput 96-well method for analyzing tannin in sorghum grain was developed. Tannin containing sorghum grain contains high levels of anti-oxidants which are reported to offer human and animal health benefits. The HCl-vanillin assay is a common and time consuming method for determining tannin content in sorghum grain, but is not efficient for screening large sample sets as seen in association trait mapping panels or breeding nurseries. ARS researchers in Manhattan, Kansas developed the 96-well micro-titer assay to assist breeders in screening these large sample sets. The high throughput 96-well method is able to perform 224 measurements compared to the 30 measurements using the common HCl-vanillin assay during the same time period. The 96-well assay may be employed to identify tannin from non-tannin sorghum grain that will assist to mitigate cross contamination of the sorghum grains.
2. Development of high throughput method for analysis of amylose to amylopectin ratios in sorghum. The composition of sorghum starch is an important factor in determining how well a given sorghum sample may work as an ingredient in human foods, as animal feed and for producing ethanol. However, many methods for determining starch composition are tedious and time-consuming. To overcome this, ARS researchers in Manhattan, KS developed a high throughput method for measuring the two major components of starch, amylose and amylopectin. This method can be used to screen large sorghum populations and assist sorghum breeders and geneticists in identifying sorghum lines with desirable starch traits for specific uses.
Blackwell, D.L., Herald, T.J., Bean, S., Gadgil, P. 2012. Alkaline extraction of phenolic compounds from intact sorghum kernels. International Journal of Food Science and Technology. p. 1-5. doi:10.1111/j.1365-2621.2012.03138.x.