EFFECT OF MILK CONCENTRATION, PH AND TEMPERATURE ON AGGREGATION KINETICS AND COAGULATION PROPERTIES OF ULTRAFILTERED (UF) MILK

Aggregation kinetics of renneted ultrafiltered (UF) milk were monitored by measuring the complex viscosity (mu*) at various times with a Nametre viscometer. The rate of aggregation increased with an increase in milk concentration (1X-4x) and temperature (28-37-degrees-C) and a decrease in pH (6.8-6-0). The coagulation time (CT) decreased with a decrease in pH from 6-8 to 6.0 and with an increase in temperature. The CT decreased with an increase in milk concentration when milk pH was unadjusted (7.0), but remained unaffected when pH was adjusted by adding lactic acid (6.8 6-0). The curd firmness index increased with an increase in both milk concentration and temperature, and with a decrease in pH. The aggregation kinetics suitably followed the Scott-Blair and Burnett model (mu* = mu*(infinity) exp (-lambda/t*)), where mu*(infinity) = limiting value of mu*, cP; lambda = time at which mu* = mu*(infinity)/e, min and t* = time after aggregation, min.