Changes of secondary structure and surface tension of whey protein isolate dispersions upon pH and temperature

Abstract

The secondary structure of proteins in unheated and heated whey protein isolate dispersions and the surface tension of the solutions were investigated at different pH. Heating protein solutions at 80°C results in an increase of unordered structure. Nevertheless, the difference between the contents of unordered structure in the unheated and heated samples increases with increasing pH of the solution. At low protein concentrations the surface tension decreased with increasing protein concentration to about 5 mg/ml. For the heated solution, a similar trend was observed in the decrease in the surface tension with increasing concentrations of protein. In both cases, the curves depicting the surface tension as a function of protein concentration could be fitted to the exponential function with a negative exponent, but with the heated solutions lower values of surface tension were observed. Studies on the surface tension of whey protein isolate solutions prove that the unfolding of whey proteins, revealed by changes in the secondary structure, causes a decrease in the surface tension.

Keywords

• circular dichroism
• globular protein
• protein concentration