Chemical and microbiological quality, capillary electrophoresis pattern, and rennet coagulation of UHT-treated and irradiated milk

Abstract

To see the possibility of irradiation as an alternative to ultra high temperature (UHT) sterilization, the quality characteristics of milk were analyzed. Milk treated by UHT (135 degrees C for 4 sec) and irradiation at higher than 3 kGy showed no viable counts after 7 days of storage at 4 degrees C. The contents of certain amino acids of milk, such as Arg, Asp, Glu, lie, Leu, Lys, Pro, Set, Thr, and Tyr, were lower in irradiated groups at 10 kGy than in UHT-treated one, but no difference was observed between irradiated milks at less than 5 kGy and UHT. The capillary electrophoresis (CE) patterns of the milk irradiated at 10 kGy showed a similar trend to the raw milk, low temperature long time (LTLT, 63 degrees C for 30 min), and high temperature short time (HTST, 72 degrees C for 15 sec) treated. However, the CE pattern of UHT-treated milk was different. Rennet coagulation test agreed with the CE results, showing that all milk samples were coagulated by refiner addition except for UHT-treated milk after 1 hr. These results suggest that irradiation of milk reduce the content of individual amino acids but it may not induce severe conformational change at a protein level when compared with UHT treatment.