Properties of UF Milk Retentates
UF retains all milk fat and protein. Lactose permeates freely through the membrane. Mineral retention is dependent on the association with proteins and decreases with acidification.
Fat globules are slightly reduced in size, indicating that some homogenization takes place in the UF system. Casein micelles and whey proteins are unaltered. Buffer capacity of UF retentates increases exponentially with total solids due to the concentration of proteins and salts
Culture growth is normal but more acidity is required to reduce pH because of the high buffer capacity of UF milk retentate..
If rennet is added proportional to milk volume rather than weight of protein, rennet coagulation time (RCT) is unaffected by UF concentration. This means that, relative to the amount of protein present, less rennet is required for coagulation. However, the structure and properties of the gel are quite different than in normal milk, and for aged Cheese there is insufficient rennet to promote ripening. Concentration by UF has the remarkable effect of restoring rennetability to over pasteurized milk.
UF activates the natural milk lipase and concentrates bacteria. However, UF retentates have superior freeze-thaw stability, less oxidative rancidity, and have greater microbiological stability.