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Isolation and characterization of the major fraction of flaxseed proteins Chung, Mavis W. Y.

Abstract

Flaxseed has not been well characterized in terms of the physicochemical and functional properties of its constituent proteins. This information is essential for its utilization. The major fraction of flaxseed proteins was isolated and characterized in this study. Proteins from NorMan flaxseeds were extracted with 0.10 M NaCl in 0.10 M Tris at pH 8.6 and fractionated by DEAE-Sephacel anion-exchange chromatography. The major protein fraction was eluted at 0.25 M NaCl and comprised 63.7 % of the total proteins. The gel electrophoretic profiles, isoelectric points, sulfhydryl and disulfide groups, and amino acid composition of the major fraction were investigated. In addition, the surface hydrophobicity, apparent viscosity, solubility and foaming properties of the major fraction in buffer conditions with two NaCl concentrations (0.01 or 1.0 M) at three pHs (3, 5 or 7) were examined. At least six different size classes of polypeptides, with predominant components having molecular weights of 20 ± 1, 26 ± 2 and 31 ± 1 kDa, were observed for the major fraction in reducing SDS-PAGE. The fraction had a high content of disulfide linkages but low content of sulfhydryl groups. Similar to the storage globulin of other oilseeds, it had high level of arginine, glutamate (and/or glutamine) and aspartate (and/or asparagine). The isoelectric points of three components in the major fraction separated by isoelectric focusing were 4.7 ± 0.0, 5.1 ± 0.0, and 5.6 ± 0.1. Its surface hydrophobicity (S0) measured by the PRODAN fluorescent probe was significantly affected by pH and NaCl concentrations. S0 increased with the addition of NaCl and increased in pH. The major fraction showed a typical U-shaped solubility curve as a function of pH at low NaCl concentration while addition of NaCl broadened and shifted the region of minimal solubility to the acidic side. The fraction had foaming properties comparable to that of a commercial egg albumen powder in 0.01 M NaCl at pH 7 and it had the densest and most stable foam in the same buffer at pH 3. Results from this thesis serve as a basis for more in-depth characterization of the major fraction of flaxseed proteins.

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