Physico-chemical properties of casein micelles reformed from urea-treated milk

Abstract

SummaryMicelles reconstituted from urea-treated milk by exhaustive dialysis against bulk milk were similar to native micelles with respect to colloidal phosphate: casein ratio, ethanol stability, heat stability and susceptibility to first-stage rennin action. Reconstituted micelles were considerably smaller than native micelles as indicated by turbidity, sedimentation and viscosity, had shorter second-stage rennet coagulation times, were unstable to [Ca2+] > 20 mM and had reduced base-binding capacity. It is suggested that the induced Ca sensitivity is due to unfavourable alterations in the micellar κ-casein coat arising from the decrease in average micelle size and can be offset by increasing the κ-casein complement of the system or by increasing the degree of aggregation by slowly raising the [Ca2+] level.