Alkaline phosphatase and microbial inactivation by pulsed electric field in bovine milk

The effects of pulsed electric field (PEF) treatments at field intensities of 25-37 kV cm(-1) and final PEF treatment temperatures of 15 degrees C and 60 degrees C on the inactivation of alkaline phosphatase (ALP), Total Plate Count (TPC), Pseudomonas and Enterobacteriaceae counts were determined in raw skim milk. At 15 degrees C, PEF treatments of 28 to 37 W cm(-1) resulted in 24-42% inactivation in ALP activity and <1 log reduction in TPC and Pseudomonas count, while the Enterobacteriaceae count was reduced by at least 2.1 log units to below the detection limit of 1 CFU mL(-1). PEF treatments of 25 to 35 W cm(-1) at 60 degrees C resulted in 29-67% inactivation in ALP activity and up to 2.4 log reduction in TPC, while the Pseudomonas and Enterobacteriaceae counts were reduced by at least 5.9 and 2.1 logs, respectively, to below the detection limit of 1 CFU mL(-1). Kinetic studies suggested that the effect of field intensity on ALP inactivation at the final PEF treatment temperature of 60 degrees C was more than twice that at 15 degrees C. A combined effect was observed between the field intensity and temperature in the inactivation of both ALP enzyme and the natural microbial flora in raw skim milk. (C) 2007 Elsevier Ltd. All rights reserved.