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United States Department of Agriculture

Agricultural Research Service

Research Project: ENHANCED END USE QUALITY AND UTILIZATION OF SORGHUM GRAIN

Location: Grain Quality and Structure Research Unit

2009 Annual Report


1a.Objectives (from AD-416)
Determine relationships between sorghum grain physical properties including hardness, diameter, and kernel weight, protein and starch composition and processing quality and identify sorghum biochemical components related to food functionality and bio-industrial uses such as ethanol production. Use knowledge of these components to improve the quality and yields of bio-industrial materials and the quality and functionality of sorghum flour which will facilitate development of new, high quality foods, especially for the gluten free food market.


1b.Approach (from AD-416)
New slope and bias curves for measuring hardness, diameter, weight and moisture of sorghum grain by the SKCS will be determined for more accurate characterization of sorghum using the SKCS. Differences in protein content and composition of isolated hard and soft endosperm fractions will be determined. Sample sets to be used for relating processing quality to protein content and composition will be collected. Samples varying in pericarp color, presence of testa layer, plant color, and kernel attributes for analysis of grain color compounds, phenolics, and other small molecules will be collected. Techniques for extracting and analyzing sorghum color compounds by HPLC and HPLC-MS will be developed.

Multi-instrument SKCS comparisons and calibrations with researchers in Kansas, Nebraska, and Texas will be completed. The effect of environment on protein content and composition of isolated hard and soft endosperm fractions will be determined. Wet milling, dry milling, extrusion and fermentation quality of selected sorghum lines will be conducted. Color compounds, phenolics, and other small molecules in sorghum from weathered and sound grain; evaluate grains for markers of insect and fungal damage and infestation will be characterized and cataloged.

Exotic germplasm will be evaluated for desirable processing traits (e.g. ethanol yield). GxE stability of processing quality in sorghum lines showing desirable processing traits will be evaluated. Impact of compounds found in sorghum grains as a result of weathering, mold, insects, or fungal invasion on food and processing quality will be determined. Processing methods to reduce or eliminate impact of environmental damage will be investigated.

Improved techniques for extracting and analyzing sorghum proteins will be developed. Methods for extracting and purifying sorghum proteins for industrial and food applications will be determined. Formulations for the production of wheat free sorghum foods from batter type systems will be optimized.

Optimization of batter type product formulations for production of wheat free sorghum based foods will be continued. Visco-elastic dough formation in artificial sorghum protein-starch dough systems will be investigated and changes to sorghum proteins during mixing will be elucidated and compared to wheat proteins during mixing. Methods for disruption of sorghum protein bodies in sorghum flour to free proteins for interaction during mixing will be developed. Starch and protein content and composition from diverse sorghum lines will be determined and related to ethanol and lactic acid yields. The extent of protein-protein interaction and protein-starch interaction in artificial sorghum dough systems will be determined. Methods for the use of reduction-oxidation systems to form a visco-elastic dough directly from sorghum flour will be developed. Sorghum proteins and starch will be modified to improve functionality in food. Pre-treatment methods for altering protein and starch composition in sorghum for improved ethanol and lactic acid yields will be developed.


3.Progress Report
Processing of sorghum grain and grain quality: Sorghum flour was milled to different particle sizes and with different extraction rates and bread made from these flours. Particle size was found to directly impact bread and noodle quality. Physical grain quality is an important factor in the processing of any grain. For sorghum, an important part of grain quality is mold resistance.

Several fungi, including Fusarium thapsinum (FT) and Curvularia lunata (CL), colonize sorghum grain during development. Several sorghum lines (Sureno, Tx2911, SC170, BTx623, BTx631, and Tx430) were experimentally infected at anthesis with both pathogens. Using the single kernel characterization system (SKCS), grain was measured for hardness, weight, moisture and diameter. Total protein and kafirins (gamma and non-gamma) were also measured. SKCS data indicated that inoculations with FT and CL reduced weight and diameter of harvested grain. Inoculations had a significant effect upon total protein accumulation in grains (P < 0.05); the response varied by genotype and treatment. Levels of gamma-kafirin also varied by genotype and treatment, whereas non-gamma varied by genotype only. Gamma-kafirin content and hardness increased in FT- and CL-inoculated 'Sureno' (GMR). Further studies are needed to elucidate the underlying structural characteristics associated with high quality grain and resistance to GM fungi. One factor related to mold resistance in sorghum is the level of phenolic compounds. Phenolic compounds were measured in a set of sorghum hybrids developed at different time periods during the last 40 years. Phenolics were measured in these samples to determine if major changes in the grain were seen over time.

Sorghum based food production: Visco-elastic dough formation in two different proteins was studied. We had previously shown that visco-elastic dough could be formed from isolated zein (maize proteins). Our research has focused on using zein as they are commercially available and therefore can easily be obtained on a sufficient scale for baking experiments. Since the zein proteins must first be isolated before they are functional, research was conducted to examine the effect of the isolation procedure on zein functionality. Proteins were also extracted from sorghum flour and the effect of isolation on their functionality examined. For the zeins, it was found that removal of lipids during the extraction appears to be a key factor in their functionality. Furthermore, the mechanism of dough formation in zein appears to be substantially different from what occurs in wheat proteins. A second type of protein, carob germ flour, was used to form visco-elastic dough. This protein was capable of forming dough without first isolating it. Bread quality of carob based dough was compared to that of wheat and sorghum breads. Carob proteins were characterized by techniques typically used to characterize wheat proteins to gain a better understanding of how they are able to form dough. It was found that unlike zein, the carob proteins appeared to form dough along similar lines as wheat proteins do.


4.Accomplishments
1. Dough formation from non-wheat proteins as models for dough formation in sorghum. Two non-wheat proteins, zein and carob germ proteins, were characterized for the ability to form visco-elastic dough similar to that of wheat. ARS scientists in Manhattan, KS found that both zein and carob germ proteins were capable of forming dough. With the carob proteins, dough formation may be similar to that of gluten. With zein isolated proteins must be used. The scientists found that the extraction method used to isolate the proteins has a major effect on the functionality of the proteins. This research showed that proteins other than wheat can form dough. This information may be used to improve the quality of non-wheat food products and in the long-term be used to improve the functionality of sorghum flour.

2. Evaluation of selected sorghum hybrids in a gluten-free noodle system. The number of people diagnosed with celiac disease has increased and subsequently the market for gluten-free products is rising. Sorghum has been identified to be a safe grain to use as a wheat alternative for the celiac community. An Asian noodle was selected as a model system because of the growing market in the US and the lack of research and availability for sorghum noodles. A series of chemical and physical analyses were conducted to compare four sorghum hybrids (Orbit, NE #8, F-525, NE #4) in a gluten-free noodle system. The noodles were formulated with 100% sorghum flour and the other functional ingredients including dried whole eggs, egg whites, xanthan gum and corn starch. Sorghum noodles were significantly different in color, texture and cooking quality among hybrids. The starch properties were found to have more affect than protein content on sorghum noodle qualities. Sorghum flour with fine particle size and low ash content was crucial for making acceptable sorghum noodles. The project demonstrated that Asian noodles formulated from sorghum F-525 exhibited physical properties that were similar to the commercial wheat flour noodles.


6.Technology Transfer

None

Review Publications
Park, S., Arthur, F.H., Bean, S., Schober, T.J. 2008. Impact of differing population levels of Rhyzopertha dominica (F.) on milling and physicochemical properties of sorghum kernel and flour. Journal of Stored Products Research 44: 322-327.

Zhao, R., Bean, S., Wang, D. 2008. Sorghum Protein Extraction by Sonication and Its Relationship to Ethanol Fermentation. Cereal Chem. 85:837-842.

Zhao, R., Bean, S., Wu, X., Wang, D. 2008. Assessing fermentation quality of grain sorghum for fuel ethanol production using rapid visco-analyzer. Cereal Chem. 85:830-836.

Schober, T.J., Bean, S. 2008. Sorghum and Maize. In: Arendt, E.K. and Bello, F.D. editors. Gluten-Free Cereal Products and Beverages. Academic Press. Chapter 5. p. 101-118.

Schober, T.J., Bean, S., Boyle, D.L., Park, S. 2008. Improved viscoelastic zein-starch doughs for leavened gluten-free breads: Their rheology and microstructure. Journal of Cereal Science. 48:755-767.

Schober, T.J., Bean, S., Wang, D. 2009. Capillary Electrophoresis as a Tool for Evaluating Lactic Acid Production from Sorghum. Cereal Chemistry. 86(2):117-121.

Sang, Y., Bean, S., Seib, P.A., Pedersen, J.F., Shi, Y. 2008. Structure and Functional Properties of Sorghum Starches Differing in Amylose Content. J of Agric Food Chem. 56:6680-6685.

Last Modified: 8/19/2014
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