Complexes of bovine serum albumin with sulphated polysaccharides: effects of pH, ionic strength and high pressure treatment

Solutions of bovine serum albumin (BSA) (5 mg ml(-1)) subjected to high pre ssure processing (600 MPa for 20 min) at low ionic strength and neutral pH have shown a reduction in protein surface hydrophobicity. This decreases fu rther in the presence of iota- or kappa-carrageenan (2.5:1 weight ratio). T he total calorimetric enthalpy (Delta H) for the pressure treated BSA is re duced by 50%. Addition of iota- or kappa-carrageenan to BSA reduces both th e denaturation temperature (T-m) and Delta H under the same treatment condi tions. Size exclusion chromatography at low ionic strength has indicated a weak electrostatic interaction for BSA + iota- or kappa-carrageenan at pH 7 , which becomes stronger at pH 6.5. Complexation of BSA with the more highl y sulphated iota-carrageenan gives a stronger electrostatic interaction tha n with kappa-carrageenan under the same solution conditions. Replacement of iota-carrageenan with dextran sulphate (DS) gives an even stronger complex , which again suggests that the strength of complexation is dependent on th e charge density on the polysaccharide. Complexation of BSA with polysaccha ride at low ionic strength appears to protect the globular protein against pressure-induced aggregation. The addition of salt dissociates the protein- polysaccharide complex(es), and the protective effect of polysaccharide is then lost. (C) 1998 Elsevier Science Ltd. All rights reserved.