Abstract:The dynamic moduli of gels filled with particles have been studied as a function of the volume fraction of dispersed particles COi (0-0.4) and of the way in which they interact with the gel matrix. Two gels of different nature were studied, viz. polyvinyl alcohol (PVA) -Congo red gels (a so-called rubber gel) and casein gels made by acidification of skimmed milk. Emulsion droplets stabilized by different macromolecules have been used as dispersed particles. If there was no interaction between the macromolecules adsorbed on the particles and the gel matrix, both the filled PVA and the filled casein gels showed a small decrease in the elastic moduli with COt, approaching the behaviour theoretically predicted for foams. In the case of interaction, the results for filled PVA gels roughly fitted the theoretical predictions, if the deformability of the emulsion droplets and the formation of an intermediate layer between the dispersed particles and the gel matrix was taken into account. The increase in the elastic modufi of the acid milk gels with C0t was much greater than expected and was probably due to aggregation of the dispersed particles during gelation.

Literature on the crispy/crunchy behavior of cellular solid foods with a crust is discussed. The emphasis is on products with a dry crispy or crunchy crust as bread and various snacks and especially on mesoscopic and macroscopic aspects. Successively, the sensory sensations involved, the mechanical and fracture behavior of crispy/crunchy products, morphological aspects, and the relation between crispy and crunchy behavior and mobility of the macromolecules and plasticizer (primarily water) involved, are discussed. Finally, some ideas for an integrated approach of crispy/crunchy behavior of cellular solid foods with a dry crust will be discussed.

No abstract

No abstract

No abstract

No abstract

Heat-induced gel formation by soy protein isolate at pH 7 is discussed. Different heating and cooling rates, heating times, and heating temperatures were used to elucidate the various processes that occur and to study the relative role of covalent and noncovalent protein interactions therein. Gel formation was followed by dynamic rheological measurements. Heat denaturation was a prerequisite for gel formation. The gelation temperature (84 degrees C) was just above the onset denaturation temperature of glycinin. The stiffness of the gels, measured as the elastic modulus, G', increased with the proportion of denatured protein. An increase in G' was also observed during prolonged heating at 90 degrees C. This increase is explained by the occurrence of rearrangements in the network structure and probably also by further incorporation of protein in the network. The increase in G' upon cooling was thermoreversible indicating that disulfide bond formation and rearrangements do not occur upon cooling.

No abstract