Influence of feed composition on stability of fat globules during pumping of raw milk

Three groups of Holstein cows were fed concentrates with different fatty acid compositions; one high in saturated lipids, another high in unsaturated lipids and the last one simulating high de novo synthesis. The feedings resulted in milk with fat contents of 5.0%, 3.7% and 4.0%, respectively. The milk fat globules (MFGs) were significantly larger in the milk with the highest fat content. All three types of milk were pumped for 450 s at various shear rates and temperatures. Afterwards, measurement of particle size distribution showed that the highest coalescence of MFGs in the milk occurred with the largest fat globules. Moreover, the fat globules were more unstable at a pumping temperature of 31degreesC compared with lower temperatures. Likewise, an increase was found in free fatty acids for milk with the largest MFGs, indicating that milk with a high fat content is more unstable when exposed to mechanical stress. Xanthine oxidase activity in raw milk was not affected by pumping. The results are discussed in relation to automatic milking systems. (C) 2003 Elsevier Ltd. All rights reserved.