597. Microscopic appearance of fat on the milk surface as affected by mechanical disturbance of the surface

Abstract

The freshly formed surface of milk or cream obtained by overflowing in a double funnel is nearly free from microscopically visible fat.When this surface is disturbed, either by repeated touching with a platinum ring or by allowing air bubbles to burst there, the fat globules and clumps are brought on to the surface, appearing there as such, or being stretched to lenses, or being spread as patches.The amount of fat brought onto the surface increases with the extent of disturbance, viz. the number of touches with a platinum ring or the number of air bubbles burst, and with the fat percentage of cream.Ageing of milk or cream slightly promotes the transfer of fat globules onto the surface.At 30° C. the bursting of about 10–15 air bubbles is enough to cover the milk surface in the overflow outfit with an almost continuous fat blanket, while at 20° C. the globules and clumps occur separately.The fat globules rendered hydrophobic by mechanical treatment of the milk surface, as well as the fat patches on the surface, are likely to be accessible to the action of lipase. This may explain the agitation activation of lipolysis in raw milk during certain stages in machine milking and during transportation.