Some observations on the nature of heated mixtures of bovine serum albumin with an alginate and a pectin

The techniques of sedimentation analysis in the analytical ultracentrifuge, relative viscosity and dynamic light scattering were used to study the effect of heat treatment on dilute solution mixtures of (i) bovine serum albumin (BSA) and a sodium alginate (Mw ~ 210 000) and (ii) BSA and a highly esterified (70%) pectin (Mw ~ 130 000)_ The two polysaccharides showed very different responses to thermal treatment, both in the presence of BSA and alone. The equivalent hydrodynamic diameter from dynamic light scattering of the pectin is reduced in the presence of the protein and both the mixture and pectin alone showed a reduction in apparent diameter with increasing heating temperature. In contrast the aiginate mixture showed a larger apparent diameter than the polysaccharide alone at high heating temperatures, a value which appeared to be highly sensitive to the temperature of heat treatment. The maximum complex size was found at the highest heating temperatures (95°C), and higher than can be accounted for simply in terms of high temperature BSA aggregation phenomena. In contrast, at 85°C the size could be accounted for by simply a weighted average of free alginate and aggregated BSA, after comparison with the appropriate controls_