Milk was heated at different pH (pH 6.5–7.1) and temperatures (20–120 C/10 min). This resulted in different leve ls of casein and denatured whey proteins to be distributed between the colloidal and serum
phases. The mil ks were subsequently acidified and the distribution of protein between colloidal and
serum was monitored at different pH. On acidification to pH 5.4, the serum phase caseins and denatured
whey proteins partially reassociated with the caseins, although a complex behaviour was observed at
pH 5.4 where additional casein dissociation occurred in some samples. At pH below 5.4 the caseins
and denatured whey proteins rapidly aggrega ted. No separate aggregation of j-casein/denatured whey
protein complexes or j-casein depleted micelles was observed. The earlier gelation of milks heated at
higher pH was likely to be due to the destabilisation of the entire milk protein system rather than a preferential aggregation of the serum phase proteins.