ASPECTS OF SCALING BEHAVIOR IN THE KINETICS OF PARTICLE GEL FORMATION

Casein micelles the colloidal particles of skim milk, are electrosteri cally stabilized by the member bf the casein protein family designated as kappa-casein, which is located In preferentially on the micellar s urface. the first stage of cheesemaking, chymosin, the active enzyme o f calf rennet, cleaves the kappa-casein molecule at a specific bond, e ventually destabilizing the micellar system and ultimately producing a curd a particle gel network where the micelles retain their integrity . No obvious change in ob fluidity of the milk is apparent for some ti me after the addition of enzyme during which period a considerable fra ction (around 80%) of the kappa-casein is proteolyzed. At the end of t his lag period, generally termed a coagulation time, a rapid aggregati on occurs and gelation follows in a quiescent sample. It Is demonstrat ed in this paper that the gelation profiles in these reactions show sc aling behaviour and can be described by an analytical function involvi ng only two independent parameters. One of these, the gel strength at infinite time, can be regarded as embodying the static attributes of t he gelation process; the other, the gelation or coagulation time, cont rols the dynamics of gel-firming when the static elements are invarian t between experimental situations. A simple mechanical model which pre dicts an inverse cubic dependence of the gel strength on particle size is then introduced, with supporting experimental verification.