Characterization and properties of flaxseed protein fractions

The albumin, globulin and glutelin fractions were fractionated from defatted flaxseed meal by sequential solvent extraction. Albumin and glutelin fractions were the predominant protein fractions, accounting for 38.1 and 33.9% respectively while the globulin accounted for 27.9%. The protein content of albumin, glutelin and globulin fractions were 64.9, 22.4 and 18.1% of the total protein. Native-PAGE patterns of albumin, globulin and glutelin, exhibited that each fraction has two bands. SDS-PAGE profile of the protein fractions showed two intense bands corresponding to 22 and 24 kDa and two bands corresponding to 9 and 33 kDa were observed from albumin. Globulin showed one intense band at 23 kDa and three minor bands, with a molecular weight (MW) of 10, 24 and 33 kDa. Glutelin showed the presence of two intense bands with a MW 22 and 35 kDa and three minor bands with MW of 35, 45 and 55 kDa. ESI-MS results were as follows; two protein subunits with MW of 9 and 27 kDa were observed with albumin, globulin indicated the presence of two subunits with MW of 17 and 28 kDa and glutelin showed the presence of one subunit with MW of 14 kDa. FTIR analysis of protein fractions suggested that alpha-helix is a common peak in all protein fractions. DSC showed that the albumin had the highest peak temperature (T d) of 122.3°C, globulin with Td of 118.3°C and glutelin with a peak temperature (Td) value of 106.8°C. RP-HPLC analysis showed more than one major component for the globulin, glutelin and albumin fractions. The albumin fraction showed two peaks; a dominant peak at a retention time of 26.2 min and one minor peak at 25.1 min. The globulin fraction demonstrated one dominant peak at retention time of 24.9 min and one minor peak at 30.4 min. Glutelin exhibited a major peak at 25.0 min and two minor peaks at 18.0 and 26.2 min.;In-vitro tryptic digestion of albumin, globulin and glutelin protein fractions indicated that the degree of hydrolysis (DH) was for glutelin with 24.5% DH, albumin with 16.0% DH, and globulin with 9.4% DH: by comparison the DH of a commercial soybean protein isolate was 14.1%. Tandem mass spectrometric (LC-ESI-MS/MS) analysis of tryptic hydrolysates resulted in the identification of some peptides from the albumin, globulin and glutelin fractions which were found to be homologous with conlinin and chitinase IV. Investigation of selected biological properties of tryptic digests of flaxseed proteins showed that the highest antioxidant (90%) and effective fungal inhibition activity was obtained with glutelin hydrolysates, while the highest ACE inhibition (60%) activity was observed with glutelin protein.