Alkaline phosphatase and microbial inactivation by pulsed electric field in bovine milk |
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Affiliation: | 1. RMIT University, School of Applied Sciences, Food Science, GPO Box 2476V, Melbourne, VIC 3000, Australia;2. Food Science Australia, 671 Sneydes Road, Private Bag 16, Werribee, VIC 3030, Australia;1. Agroscope, Institute for Food Sciences, Schwarzenburgstr. 161, 3003 Bern, Switzerland;2. National Reference Laboratory for Milk and Milk Products (EURL), Avenue du Général de Gaulle 23, 94706 Maisons Alfort Cedex, France;3. Department of Food, Environmental and Nutritional Sciences (DeFENS), University of Milano, Via Celoria 2, 20133 Milano, Italy;1. School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4, Ireland;2. School of Veterinary Medicine, University College Dublin, Ireland;1. Department of Food Science, University of Otago, Dunedin, New Zealand;2. Riddet Institute, Palmerston North, New Zealand |
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Abstract: | The effects of pulsed electric field (PEF) treatments at field intensities of 25–37 kV cm− 1 and final PEF treatment temperatures of 15 °C and 60 °C on the inactivation of alkaline phosphatase (ALP), Total Plate Count (TPC), Pseudomonas and Enterobacteriaceae counts were determined in raw skim milk. At 15 °C, PEF treatments of 28 to 37 kV 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 kV cm− 1 at 60 °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 °C was more than twice that at 15 °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.Industrial relevanceMilk has been pasteurised to ensure its safety and extend its shelf life. However, the need for retaining heat-sensitive nutrient and sensory properties of milk has resulted in interest in the application of alternative technologies. The results of the current study suggest that PEF as a non-thermal process can be employed for the treatment of raw milk in mild temperature to achieve adequate safety and shelf life while preserving the heat-sensitive enzymes, nutrients and bioactive compounds. |
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