Macromolecular complexes of the main storage protein of Vicia faba seeds with sulfated polysaccharide

Specific interaction between legumin from Vicia faba seeds and kappa carrageenan at neutral pH (7.3) and low ionic strength (0.01) and the mechanism that leads to increased conformation stability and a decreased aggregation of the protein by addition of the polysaccharide were investigated using high sensitivity differential scanning calorimetry (DSC), circular dichroism (CD), fluorescence (FLU), the size exclusion chromatography equipped with an online multi-angle light scattering detector (SEC-MALS), turbidimetry and a methylene blue spectrophotometric methods (MBS). Kappa carrageenan (kCG) molecules are able to form with legumin at room temperature a water soluble interpolymeric complex. Complex formation leads to a small perturbation and loosening of the secondary structure of the protein. On the contrary, conformation stability and the stability of the protein molecules with respect to thermo aggregation are noticeably increased. It also reduces the extent of thermal modification of secondary and tertiary structure of legumin due to growth of the net charge of a protein and weakening interaction between similar protein molecules. The joint analysis of SEC-MALS and MBS shown the process is proceeded with a high the degree of conversion (>0.8) and the complexes formed are equimolar.