Influence of Protein Particles Size on Milk Sedimentation Rate from Cow and Goat after Heat Treatment

Abstract:

In the paper influence of particles size on protein sedimentation rate from cow and goat after heat treatment（95 ℃，15 min）were explored. Centrifugal sedimentation，atomic force microscope，laser particle size analyzer，and SDS-PAGE methods were used to determine protein precipitation rate，and protein surface morphology after heat treatment，casein composition，and protein particle size of fresh milk respectively. The results showed that protein sedimentation rate of goat milk was significantly higher than that of cow milk（P < 0.05），protein particles size of goat milk were significantly bigger than that of cow milk，the clumping together degree（35 858.15 nm2） of goat milk protein were bigger than that （18 215.18 nm2） of cow milk，fresh cow milk protein particle size mainly focused on 1 nm or less，that of fresh goat milk protein mainly distributed during the range of 1～1 000 nm，fresh cow milk and goat milk have two kinds of casein mainly，beta casein and alpha s1-casein，and their molecular weight are 34 000 and 26 000 respectively. Thermal stability of cow milk is better than that of goat milk. Protein particle size is the direct influence factor on the thermal stability of milk protein. Atomic force microscopy combined with laser particle size analyzer is an effective way to analyze the particle size of milk protein.