Impact of size distribution of milk fat globules on milk quality affected by pumping

In the present study a correlation (r2=0.54) was found between average diameter of the milk fat globule (MFG) and the diurnal fat yield of cows. The changes in size distribution of MFGs showed transition of medium size globules into large globules with increased fat yield. Furthermore, analysis of fatty acid composition demonstrated that the content of stearic and palmitoleic acids correlated positively with the average diameter of the MFG, while the content of polyunsaturated fatty acids correlated negatively. The importance of the size distribution of milk fat globules was demonstrated in an experiment where 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 diets resulted in milk with fat contents of 5.0, 3.7 and 4.0%, respectively. The milk fat globules were significantly larger in the milk with the highest fat content. All three types of milk were pumped at various flow rates and temperatures. Afterwards, analysis of fat globule size distribution showed that the highest coalescence of milk fat globules in the milk occurred with the largest fat globules. Furthermore, the fat globules were less resistant against coalescence at a pumping temperature of 31°C compared with lower temperatures. Likewise, an increase was found in free fatty acids for milk with the largest milk fat globules, indicating that milk with a high fat content is more unstable when subjected to pumping.