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

Particulate gels, especially those formed from heating protein solutions, h ave been extensively investigated over the years. One focus of this work ha s been, for commercial reasons, on rather crude mixtures of the main milk p rotein components (whey isolates), beta -lactoglobulin and alpha -lactalbum in. Moreover, most previous Work has concentrated on examining structural a nd theological properties of fully cured gels. In the present paper, a less pragmatic approach is adopted, and the gelation behavior of solutions of r elatively pure beta -Lg (under isothermal heating at 80 degreesC) are inves tigated over a range of concentrations and pH values (7, 3, 2.5, and 2). Bo th gel time and limiting (extrapolated) long-time modulus data were measure d and were considered in light of currently available models for the gelati on 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 ad equately understood in terms of branching theory (cascade theory descriptio n) results, corresponding well with conclusions from structural studies of the gels using negative-staining electron microscopy. A fractal model was m uch less successful in this respect. Gel time data, it seems, reflect much more sensitively the details of network assembly in a particular case. Modu lus-concentration data, on the other hand, are less determined by gel type and more universal.