Interactions of ovalbumin with sulphated polysaccharides: effects of pH, ionic strength, heat and high pressure treatment

Ovalbumin in solution (0.5-5 mg/ml), when subjected to high pressure treatm ent (>400 MPa for 20 min) or thermal treatment (>70 degrees C for 1-2 min) at pH 6.5 or 7.0, was found to become denatured and some aggregates were fo rmed. ANS studies have shown that the protein surface hydrophobicity increa ses by 600% after pressure treatment (600 MPa for 20 min) and 55% after the rmal treatment (80 degrees C for 1 min). Addition of polysaccharide (dextra n sulphate (DS) or iota-carrageenan) (1 : 0.5 by weight) to the native prot ein at low ionic strength leads to no change in fluorescence intensity or s hapes of size exclusion chromatography profiles. The presence of DS in the thermally processed samples appears to inhibit the formation of aggregates. Pressure processing (600 MPa for 20 min) at pH 7.0 was found to lead to we ak electrostatic interactions between ovalbumin and DS, which became strong er at pH 6.5. The replacement of DS with L-carrageenan in the pressure trea ted sample, under the same experimental conditions, was found to give no in teraction at pH 7.0, but a weak interaction at pH 6.5. It appears that the strength of complexation of ovalbumin with sulphated polysaccharides is dep endent on the charge density on the polysaccharide. Complexation of polysac charide with ovalbumin at low ionic strength seems to protect the protein a gainst pressure-induced aggregation. But, addition of 0.5 M NaCl dissociate s the complex(es), and the protective effect of the polysaccharide is lost. (C) 1999 Elsevier Science Ltd. All rights reserved.