Protein Modifications after Foxtail Millet Extrusion: Solubility and Molecular Weight

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.

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