Number of thiol groups rather than the size of the aggregates determines the hardness of cold set whey protein gels

Variation of protein concentration during heating resulted in the formation of protein aggregates with clearly different structural and chemical characteristics. Heating conditions were chosen such that differences in the degree of aggregation were excluded. Acid induced gelation of dispersions of these aggregates resulted in gels with clearly different hardness. Although gel hardness seemed to correlate with the different structural aggregate features as reported before in literature, the differences in hardness could for the most part be cancelled by blocking of the thiol groups. Application of thiol-blocked protein aggregates enabled us to make a distinction between the effect of structural- and chemical-properties of the aggregates. Formation of larger disulfide cross-linked protein structures paralleled the increase in gel hardness and dominated the effect of structural characteristics on mechanical properties of cold-set gels. In addition, the effect of the presence of native non-aggregated protein on the final gel properties can be excluded, since in our gel-experiments most protein (>95%) participated in the formation of a protein network. Therefore, we can conclude that the hardness of cold set whey protein gels is determined by the number of thiol groups rather than by the size of the aggregates or other structural features.