Rennet coagulation of milk subjected to high pressures.

摘要

Milk was subjected to pressures of 100-400 MPa at a rate of 2.5 MPa/s for 10-60 min. The initial rate and extent of the enzymic phase of coagulation, determined on the basis of the release of caseinomacropeptides (CMP) soluble in 4% trichloroaceticacid, were inhibited by pressures >200 MPa. However, the coagulation time decreased as pressure increased up to 200 MPa and then increased again, until at 400 MPa, it reached values comparable with those of the raw milk. Therefore, the coagulation time of the pressurized milk was not directly related to the degree of kappa-casein hydrolysis, indicating that pressure probably favoured the aggregation phase. Addition of CaCl2 enhanced casein aggregation of native or pressurized milk, reducing coagulationtime and curd-firming time, but did not offset the rate-increasing (up to 200 MPa) or rate-lowering (at 300 and 400 MPa) effects of milk pressurization on subsequent casein coagulation by rennet. SDS-PAGE studies of pressure-treated and untreated milk orsolutions containing kappa-casein, beta-lactoglobulin or both in the presence or absence of denaturing agents showed evidence for the formation of aggregates linked by intermolecular disulfide bonds.