Production of brined soft cheese from frozen ultrafiltered sheep's milk. Part 1. Physicochemical, microbiological and physical stability properties of concentrates

Abstract

Some physicochemical, microbiological and physical stability changes in sheep's milk as a result of its concentration by ultrafiltration (UF) and long-term deep-frozen storage were studied. Skim milk was concentrated by UF to 19.37, 23.40 or 26.49% total solids (TS), mixed with cream to obtain recombined UF concentrates with 30.40, 33.95 or 36.90% TS, respectively, and then frozen and stored at −20 °C for up to 6 months. With the exception of highly concentrated milks frozen for 6 months, no significant differences in lipolysis (acid degree value) and fat oxidation (peroxide value) were observed between the control milk and the UF milk concentrates stored frozen for up to 6 months. The UF process resulted in significant increases in the bacterial and coliform counts in sheep's milk, which decreased during the frozen storage. The UF concentrates exhibited good protein stability throughout frozen storage, except for one obtained from milk to which 0.5% NaCl was added before UF, which destabilized after 2 months frozen storage.