Aggregation of rennet-altered casein micelles at low temperatures

The rennet-induced coagulation of bovine milk at 10°C was investigated. The rate of change of absorbance at 600 nm was higher in milk renneted at 30°C than that at 10°C. The amount of casein sedimented on centrifuging skim milk at 5000g for 1 h at 10°C increased with time after renneting. The viscosity of milk at 10°C at low shear rates did not change significantly until 10 h after rennet addition, but it increased markedly after 20 h. Smaller particles in milk at 10°C disappeared slowly over 36 h after rennet addition and aggregated into larger particles. These results suggested that casein micelles in milk aggregate at low temperatures. Reasons for the slow aggregation of milk renneted at 10°C were investigated by inhibiting chymosin activity by pepstatin A. It is likely that β-casein, or its hydrolysis, plays a role in aggregation of rennet-altered casein micelles at low temperatures.