42-7 |
To understand the protein chemistry during extrusion of defatted peanut flour |
A. SHAH, M. Corredig, and R. D. Phillips. Dept. of Food Science & Technology, Univ. of Georgia, Food Science Bldg., Athens, GA 30602-7610 Extrusion cooking of peanut flour provides unique processing features because of the high pressure in combination with severe shear forces and high temperature the peanut flour is subjected to. During extrusion, proteins are susceptible to conformational changes and interactions of covalent and non-covalent nature. By using different solvents to selectively solubilize the protein aggregates, these interactions have been examined. Our objective was to determine the effect of extrusion conditions on protein-protein interactions. Defatted peanut flour (1.5 % fat) was extruded under different conditions of temperature (125-175 °C) and moisture (25-35 %) on a co-rotating twin-screw extruder (APV Baker) using a severe screw configuration to ensure maximum energy input. A sequential extraction procedure with three buffers: phosphate-NaCl, phosphate-urea and phosphate-urea-DTT was employed and the buffer soluble fractions were analyzed by SDS-PAGE, ion-exchange and size exclusion chromatography. SDS-PAGE revealed differences in composition of protein aggregates soluble in the 3 different buffers. Extrusion of peanut proteins caused the formation of aggregates characterized by non-covalent and disulfide interactions. Ion-exchange chromatography showed differences in the charges of the protein aggregates. Fractions soluble in phosphate buffer contained a larger amount of unbound protein in samples extruded at 175 °C. Large soluble aggregates were absent in all the extruded samples after extraction with phosphate buffer, and low molecular weight proteins (< 13 kDa) increased. In fractions soluble in urea, the large aggregates decreased with increasing extrusion temperature. On the other hand, in fractions soluble in urea-DTT, the large aggregate peak increased with increasing temperatures. This approach to study protein extrusion by separating fractions extracted with various buffers by charge and size provided a better understanding of the interactions occurring in peanut proteins. Screw configuration, temperature, and moisture affected the protein-protein interactions. This knowledge can be utilized to optimize these interactions by modifying the extrusion conditions.
Session 42, Food Chemistry: Proteins II
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