Microstructures of β-lactoglobulin/amylopectin gels on different length scales and their significance for rheological properties

Different microstructures of β-lactoglobulin gels, generated by adding non-gelling potato amylopectin of varying concentrations and rheological behaviour, were characterised by microscopic techniques on several length scales. The overall network microstructure of the β-lactoglobulin gels was analysed by using light microscopy (LM) and confocal laser scanning microscopy (CLSM), while the construction of the separate strands was investigated by using transmission electron microscopy (TEM). At an overall level of structure, increased concentration of amylopectin resulted in a more open network with larger pores and coarser clusters of aggregated protein. Examination of the microstructure of one cluster showed that increased concentration of amylopectin resulted in a more close-packed structure of aggregated protein particles. Thus, the results of the studies on different length scales showed that gels with an open protein network structure at an overall level were constructed of close-packed clusters, while gels which were dense at an overall level of structure were constructed of open and porous clusters. By using TEM at high magnifications it was possible to observe the particles forming the aggregates building up the clusters. The particles had about the same diameter, perceived to be 100–200 nm in all the types of gels studied. By studying thick sections of the microstructure in the light microscope, differences in connectivity of the protein network strands were possible to detect. The results from the microstructural investigations were analysed together with the rheological properties of the gels. It was found that the cluster size and the pore size between the strands of clusters were related to storage modulus and stress at fracture as long as the connectivity of the network strands was good.