Monitoring the changes in UHT whole milk during storage under dynamic and constant temperature profiles

Abstract

The objective of the study was to monitor some physical and chemical changes of UHT whole milk stored under constant and dynamic temperature. UHT milk samples were stored at constant room temperature (25 °C) and at constant abuse temperature (41.5 °C). Dynamic condition was attained by switching the samples between 25 and 41.5 °C with 24 h intervals up to 158 days. Physical and chemical analyses revealed that most dramatic changes obtained in samples stored at 41.5 °C followed by dynamic temperature and 25 °C. The changes in the samples stored dynamically were in between but closer to those of stored at 25 °C. The pH levels reduced, and acidity, electrical conductivity and viscosity increased at the end of the storage period (158 days). Brown color was apparent for the samples stored at 41.5 °C and samples stored dynamically had also darker color than that of the samples stored at 25 °C whereas color of freshly UHT processed milks was indistinguishable from the samples stored at 25 °C. Our results indicate that shelf life studies based on isothermal conditions should be reconsidered for UHT milk since it is almost impossible to attain constant temperature during shipment or storage.