Food Structure


Understanding the gelation behaviour of proteins is of importance in order to be able to influence the properties of many food systems and it may lead to proposals for product or process improvement . In this context the formation of heat-set ovdl bumin gels. in different media , has been studied by microstrucmral. rheological and conformational observations. An oval bumin/ water geL prepared at pH 5, shows a granular. inhomogeneous microstructure. At this pH the re are both many interand intramolecu lar interactions. and network formation occurs via aggregates of folded, globular protein chains. On the other hand , gels prepared at pH 10 or in urea solution (6 or 8 mol/1), show a unifOrm , homogeneous microstructure. Under these con· ditions. network formation occurs via flexible . unfolded pro· tein chains. The ultimate properties of the gels are well in accor· dance with these microstru ctural observat ions: with respect to the deformation at break it is found that the network composed of flexible unfolded protein chains (pH 10. urea) can be extended further withoUI breaking. leading to a higher breaking stress. than the network composed of sphe rical aggregates of strongly inte racting prote in molecules (pH 5). In the latter case the regions of low protein concentrat ion will act as weak points and consequently these gels will break at a lower stress than the gels with a more homogeneous microstructure. A study to determine whether glutaraldehyde acts as a proper fixative revealed that this compound very effectively maintains the original gel structure.

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