Cold-set globular protein gels: interactions, structure and rheology as a function of protein concentration.

We identified the contribution of covalent and noncovalent interactions to the scaling behavior of the structural and rheological properties in a cold gelling protein system. The system we studied consisted of two types of whey protein aggregates, equal in size but different in the amount of accessible thiol groups at the surface of the aggregates. Analysis of the structural characteristics of acid-induced gels of both thiol-blocked and unmodified whey protein aggregates yielded a fractal dimension (2.3 +/- 0.1), which is in line with other comparable protein networks. However, application of known fractal scaling equations to our rheological data yielded ambiguous results. It is suggested that acid-induced cold-gelation probably starts off as a fractal process, but is rapidly taken over by another mechanism at larger length scales (>100 nm). In addition, indications were found for disulfide cross-link-dependent structural rearrangements at smaller length scales (<100 nm).