Heat-induced gelation of globular proteins:: 4.: Gelation kinetics of low pH β-lactoglobulin gels

Particulate gels, especially those formed from heating protein solutions, have been extensively investigated over the years. One focus of this work has been, for commercial reasons, on rather crude mixtures of the main milk protein components (whey isolates), beta -lactoglobulin and alpha -lactalbumin. Moreover, most previous Work has concentrated on examining structural and theological properties of fully cured gels. In the present paper, a less pragmatic approach is adopted, and the gelation behavior of solutions of relatively pure beta -Lg (under isothermal heating at 80 degreesC) are investigated over a range of concentrations and pH values (7, 3, 2.5, and 2). Both gel time and limiting (extrapolated) long-time modulus data were measured and were considered in light of currently available models for the gelation process. Whereas the gel time data was described best by a semiempirical model introduced by one of the authors, the modulus data could be quite adequately understood in terms of branching theory (cascade theory description) results, corresponding well with conclusions from structural studies of the gels using negative-staining electron microscopy. A fractal model was much less successful in this respect. Gel time data, it seems, reflect much more sensitively the details of network assembly in a particular case. Modulus-concentration data, on the other hand, are less determined by gel type and more universal.