Abstract:

The evolution of heat stability, emulsifying properties and turbidity of skimmed yak milk and casein
solution was studied during exposure to elevated temperatures (30 to 90 ℃, at each temperature for 15 min).
Meanwhile, scanning electron microscope (SEM) was applied to observe the change on the surface of the casein
micelles in the solution during the processes. As a result, due to the interaction of whey proteins with casein, the
dissociation and aggregation of casein itself occurring as the temperature was increased, the heat stability and
emulsifying properties of skimmed yak milk and casein solution were decreased, and turbidity was increased.
Additionally, the variation range of skimmed milk was obviously larger than that of pure casein solution. As
the temperature was increased from 70 to 90 ℃, the precipitation capacity of skimmed yak milk was increased
from 1.46% to 3.19%, and casein solution presented a smaller change. Both EAI and ES declined with increased
temperature. The turbidity of skimmed yak milk significantly increased (P ＜ 0.05) at heating temperatures above
60 ℃, and the casein solution showed a linear increase from 0.28 to 0.33.

Key words: yak milk, casein, heat stability, emulsifying properties, turbidity