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), -lactoglobulin and R-lactalbumin. Moreover, most previous work has concentrated on examining structural and rheological properties of fully cured gels. In the present paper, a less pragmatic approach is adopted, and the gelation behavior of solutions of relatively pure -Lg (under isothermal heating at 80°C) 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.

A method for particle sizing using a commercial spectrophotometer is presented, based on a Rayleigh-Gans-Debye treatment of the wavelength dependence of turbidity. The finite acceptance angle of the spectrophotometer has been taken into account and shown to be potentially advantageous. The method has been used to monitor the kinetics of droplet growth in phase separating biopolymer mixtures of gelatin and maltodextrin, and predicted droplet sizes have been compared with data obtained from confocal laser scanning microscopy. Furthermore, the temperature dependence of the turbidity data is used to construct a model of the phase behavior of the biopolymer mixture. For systems demixing between 60 and 30 °C, the driving force for phase separation is solely governed by the temperature-dependence of the Flory-Huggins interaction parameters. Below 30 °C the gelatin ordering triggers additional driving forces for phase separation and subsequently leads to the formation of a gel network that traps the system microstructure.

Experimental and theoretical investigations of the swelling and mechanical properties of hydrogels formed from chitosan, bovine serum albumin (BSA), and chitosan/BSA mixtures cross-linked with genipin were performed. The properties of cross-linked chitosan hydrogels were explained in terms of its polyelectrolyte behavior, which led to a gradual increase in swelling ratio below the pK value, but whereby its swelling ability was eliminated by the presence of salt that screened the charges. Comparison of theoretical and experimental calculations of the swelling ratio, however, indicated that complications arising from wastage of cross-links, and formation of polymerized genipin cross-links must be considered before quantitative prediction can be achieved. Cross-linked BSA hydrogels swelled even in the presence of salt, and a marked increase in swelling was observed below pH = 3 that was explained as the result of an acid induced denaturation of the protein that led to unfolding of the molecule. Swollen BSA hydrogels were mechanically weak, however. Composite gels made from a cross-linked mixture of chitosan and BSA exhibited the swelling behavior of BSA combined with the mechanical properties of chitosan and were therefore considered most suitable for use in a gastric environment.