Mesoscopic structure and viscoelastic properties of β-lactoglobulin gels at low pH and low ionic strength

Abstract

In this paper, we have investigated the mesoscopic structure and rheological properties of heat-set β-lactoglobulin gels at low pH and low ionic strength. We have determined the scaling of the elastic or storage modulus of the gel with protein concentration. Four batches with a pH of 2 and an ionic strength of 13 mM showed a wide range of scaling behavior. In two of the batches, two concentration regimes with distinctive exponents could be detected. We constructed the phase diagram for this system as a function of pH and ionic strength, and were able to show that the wide spread in scaling behavior between the batches is the result of differences in the mescopic structure of the gels. These differences in mesoscopic structure were the result of small variations in pH and ionic strength between the batches. Our experiments show that when characterizing gel properties of β-lactoglobulin solutions at very acidic conditions and low ionic strength, extreme care has to be taken to stabilize the pH of these systems. Small variations in pH have a drastic effect on the structure of the gels, and on the macroscopic viscoelastic properties.