I. J. Kopelman

Effects of microwave reheating on surimi gel texture

Microwave re-heating of a surimi gel may change its mechanical properties by introducing defects into the protein gel matrix. These defects result from the localized hot spots that are generated due to the non-uniform nature of microwave heating, especially at high output power. When the temperature at these hot spots is above the boiling point, the resulting high water vapor pressure may overcome the gel cohesion forces and create structural defects. This phenomenon will not take place in the absence of loci having a temperature above boiling point. The latter is the case when re-heating is done by hot water, steam, low power microwave, and even by high-power microwave, as long as the temperature is well below the boiling point. The structural changes due to these defects seem to weaken the gel structure, which is opposite to the effect caused by moisture lost.

The effect of topological constraints on polymer network pressure

Recent data on comparative osmotic deswelling of poly(acrylic acid) gels and solutions shows that the difference between osmotic pressure of the gel and of the solution, P gel (c, f) - P solution (c,f ), taken at equal polymer concentration (c) and fraction of the ionized acrylic acid monomers (f), changes its sign from negative to positive as the concentration c increases; this effect is enhanced with increasing f whereby it is shifted toward lower concentrations. In order to explain this effect, a model is suggested for the elastic pressure of the gel network which takes into account the effect of topological constraints combined with the effect of network ionization. According to the model, the sign-change of P gel - P solution originates from the topological constraints on conformations of the network; the ionization of the network chains enhances this effect and shifts it to the concentration range of the experiment.