Extended Storage of Raw Milk. II. The Role of Thermization

Abstract

Raw milk was thermized in a pilot scale heat exchanger at 62, 65 and 70°C for 10 and 20s and then stored at 4°C for up to six days. Effectiveness of these heat treatments on quality of milk was assessed by Standard Plate Count (SPC), Psychrotrophic Bacteria Count (PBC), Tyrosine Value (TV), free fatty acids (FFA), lipase activity and organoleptic analyses. Thermizing resulted in reduction of SPC and PBC with distinct differences at each processing temperature. A treatment of 65°C for 20s is recommended since this was the minimum which provided the desired shelf life extension of four days. This heat treatment resulted in slightly over 50% reduction in lipase activity. Little change in lipase activity, FFA content, TV and flavor occurred during the first four days of storage, but after that time increases in the last three measurements were detected. It is suggested that thermization may be used in the dairy industry where raw milk is being transported and stored for extended periods of time prior to processing.