THE EFFECTS OF COMPOSITION AND SOME PROCESSING TREATMENTS ON THE RENNET COAGULATION PROPERTIES OF MILK

The effects of various processing parameters on the rennet coagulation properties of milk were assessed. Using low amplitude oscillation rhe ometry, the coagulation properties were monitored by measurement of th e elastic shear modulus, G', as a function of rime, t, from rennet add ition; G' was taken as a measure of curd firmness. The Scott-Blair rim e dependency model was fitted to the experimental G'/t curves for the determination of the following coagulation parameters: gel time, maxim um curd firming rate, the set-to-cut time at 20 Pa tie, time to reach 20 Pa) and the curd firmness after a renneting time of 2400 s. The ren neting properties were enhanced by increasing the levels of milk prote in and fat in the ranges 0.3-7.0% (w/w) and 0.1-10% (w/w) respectively and by two stage homogenization pressure where the first stage pressu re, P-1, was varied from 0 to 25 MPa and the second stage pressure, P- 2, was held constant at 5 MPa. The influence of these parameters, with in. the range investigated, in complementing the gel forming propertie s decreased in the following order: protein > fat > homogenization pre ssure. In contrast, the coagulation properties of milk were impaired b y high heat treatment, the addition of a commercial microparticulated whey protein based fat substitute and by partial replacement of protei n with fat.