Abstract
With the aim of illustrating the effects of extrusion cooking on the solubility of proteins in foxtail millet and their molecular basis, foxtail millet was extruded at five barrel temperature profiles and feed moisture contents. The proteins of raw and extrudate samples were extracted with six solutions sequentially. Sodium Dodecyl Sulfate- Polyacrylamide Gel Electrophoresis (SDS-PAGE) of total protein and Starch Granule-Associate Protein (SGAP) was performed. Extrusion caused a significant decrease in globulin, setarin and glutelin fractions with a corresponding increase in SDS- and SDS+2-ME-soluble and residual fractions. Increasing extrusion temperature or moisture content all led to SDS-soluble fraction decrease, while SDS+2-ME-soluble fraction increase. SDS-PAGE demonstrated that disulfide bond cross-linking occurred among glutelin and with setarin subunits. Extrusion had a less pronounced impact on the 60 kDa SGAP than the other middle-high molecular weight subunits. It is the protein- protein interaction shift from electrostatic force to hydrophobic and/or hydrogen forces and covalent disulfide cross- links that contributed to the decreased solubility of protein in foxtail millet extrudates.
Highlights
Foxtail millet (Setariaitalica), rich in the minerals and phytochemicals (FAO, 2008), is a nutritious food ingredient in traditional diet, especially for people in Europe, Asia and Africa
The purpose of this study was to determine the effects of extrusion temperature and moisture content on protein solubility in water, NaCl, ethanol and NaOH, Sodium Dodecyl Sulfate (SDS) and SDS+2-ME solutions and SDS-PAGE behavior of total protein and Starch Granule-Associate Protein (SGAP) caused by extrusion of foxtail millet
For determining the extracting duration for extrudated foxtail millet protein, Three gram of C3 extrudate was extracted with 50 mL of 5% NaCl and 1% SDS solutions
Summary
Foxtail millet (Setariaitalica), rich in the minerals and phytochemicals (FAO, 2008), is a nutritious food ingredient in traditional diet, especially for people in Europe, Asia and Africa. Extrusion cooking can be utilized to manufacture various types of foods with the advantages of high productivity and energy efficiency, low cost and zero effluents, etc., (Guy, 2001). Considering its less exploration for food usage, extrusion cooking may become an effective way for producing foxtail millet-based foods. Osborne procedure (Osborne, 1924) is often utilized in cereal chemistry to extract cereal protein fractions sequentially using water, NaCl, ethanol and acid or alkaline solutions. The resulting protein fractions are called albumin, globulin, prolamin (termed setarin for millet) and glutelin, respectively
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