Formation and structure of acidified milk gels

This paper reviews the modern concepts of gels and gelation and considers gel formation by acidification of milk in their light. From the basic definition of a gel and its description in terms of the network architecture, we present the evidence for considering yogurt as a particle gel. Using small deformation rheology to monitor the gelation of individual milks induced by the hydrolysis of glucono-delta-lactone, we demonstrate that their kinetic gelation profiles show a scaling behaviour and that the mechanism of gelation is modified by pre-heat treatment of the milk. This kinetic behaviour is considered in the light of three theoretical models, namely the adhesive sphere, percolation and fractal models. It is concluded that all fail in some respect and that further theoretical developments are required to explain the kinetics of gel formation in these systems. (C) 1999 Elsevier Science Ltd. All rights reserved.