The effect of stage of lactation and somatic cell count on the age-gelation of UHT milk

Milk production in the major dairy areas of Australia is highly seasonal, being based on pasture feeding of herds synchronized to commence lactation in early spring. This leads to large seasonal variations in milk volume and milk composition. Australian UHT milk processors report that spring and late-autumn milk often has a reduced shelf life due to age-gelation problems. Age-gelation of UHT milk is thought to be initiated by proteolysis of milk proteins by heat-resistant proteinases of bacterial origin and/or native milk proteinases. Higher concentrations of native milk enzymes are usually present in late-lactation milk and milks with a higher somatic cell count (SCC). An experiment was undertaken to examine the effect of stage of lactation and somatic cell numbers on the gelation time of UHT milk.