Submitted to: Cereal Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/14/2006
Publication Date: 10/15/2006
Citation: Park, S., Bean, S., Wilson, J.D., Schober, T.J. 2006. Rapid isolation of sorghum and other cereal starches using sonication. Cereal Chemistry. 83(6):611-616. Interpretive Summary: Sorghum starch plays an important role in both the production of sorghum food products and fermentation of sorghum to produce products like fuel ethanol. To improve the utilization of sorghum, it is necessary to understand the physical and chemical properties of its starch. Research on starch usually requires the use of purified starch. There are no rapid, simple methods for isolating sorghum starch available. Therefore, we investigated the use of ultrasound (sonication) as a method for sorghum starch purification. We found that under optimum conditions a high purity starch could be isolated with only 2 min of sonication. Starch could be isolated from either sorghum flour or sorghum whole meal. Other cereal starches from whole wheat meal, wheat flour, corn, rice, and barley were also rapidly obtained using this method. This method can be used to rapidly purify starch for analytical tests and could possibly be scaled up for use as an industrial starch isolation method.
Technical Abstract: High intensity ultrasound (sonication) was investigated as a method to rapidly purify starch from sorghum and other cereal grains. To improve the process, buffers were optimized to solubilize sorghum proteins in combination with the sonication. Protein content and starch color were determined to evaluate the efficiency of the extraction process. Sonication times, SDS concentration, different types and concentrations of reducing agents (sodium metabisulfite, dithiothreitol, and ''mercaptoethanol), and centrifugation speeds of the starch washing procedure were tested. Protein content of isolated sorghum starch was reduced to 0-0.14% (db) after a 2-min sonication (using any of the reducing agents tested). Sodium metabisulfite was chosen as the preferred reducing agent because of its lower toxicity and odor compared to other reducing agents tested. The optimum conditions for producing high purity sorghum starches (0.06% protein) were obtained using the following conditions: 2 min sonication time with 12.5 mM sodium borate buffer, pH 10 containing 0.5% SDS (w/v) and 0.5% sodium metabisulfite (w/v) using 1500 rpm centrifugation speed during starch washing. Starches separated by this method showed significantly less protein content and b values (yellowness) compared with starches separated by enzymatic methods or methods using NaCl solutions and protein extraction buffers with multiple washing steps, both of which take several hours to complete. Differential scanning colorimetry thermogram values for starches isolated by three different methods showed similar patterns except starches obtained with the enzymatic method had slightly higher values of To, Tp, and change of H. Other cereal starches from whole wheat meal, wheat flour, corn, rice, and barley were also rapidly obtained using sonication.