Effects of ambient temperatures on viscometric change of ultra-high temperature processed cow milk

The viscosity of ultra-high temperature (UHT) processed cow milk changing with temperature in the range of 20℃ to 45℃ were determined by TA AR-G2 rheometer and the data were fitted by 1stOpt1.5 Pro software, in order to evaluate the applicability of Arrhenius model to describe the course, explore the influence of ambient temperature on the shelf-life based on Stokes’ law and establish theoretical basis of accelerated shelf-life testing for UHT milk. The results showed that, in the range of 20℃ to 45℃, the viscosities of UHT milk slightly increased from 20℃ to 25℃ and then significantly decreased as the temperature rising, however gradually increased during cooling from 45℃ to 20℃. The fittness of Arrhenius model to describe the viscosity changes during heating was significantly affected by weak gel formed between κ-carrageenan and casein. When temperature was elevated to 25℃, the weak gel was disrupted and thereafter the viscosity changes of the system obeyed Arrhenius model well (R2=908). The viscosity changes during cooling also followed Arrhenius model (R2=0.942). Hence, Arrhenius model is fit for describing the temperature-dependency viscosity changes in the UHT cow milk.