Dairy Chemistry And Biochemistry

116 DAIRY CHEMISTRY AND BIOCHEMISTRY

PLASMA

7

\

Whey protein

FAT

Figure 3.25 Schematic representation of the membrane of fat globules in homogenized milk

(modified from Walstra, 1983).

4. The heat stability of whole milk is reduced by homogenization, as is the
   strength (curd tension) of rennet-induced gels; these changes will be
   discussed in more detail in Chapters 9 and 10. Viscosity is increased for
   unidentified reasons, probably independent of size changes. Homogenized
   milk has improved foaming characteristics, a feature which may be due
   to the release of foam-promoting proteins from the natural membrane or
   to reduction in fat globule size - small globules are less likely to damage
   foam lamellae. Homogenization reduces surface tension, possibly due to
   inclusion of very surface-active proteins in the artificial membrane and to
   changes in the fat globule surface. Homogenized milk drains cleanly from
   the sides of a glass bottle or drinking glass. Milk for homogenization
   should be clarified to avoid sedimentation of leucocytes.

The efficiency of homogenization may be assessed by microscopic exam-
ination or more effectively by a particle sizer, e.g. Malvern Mastersizer.

3.10.4 Heating

Normal HTST pasteurization causes very little change in the fat globule

membrane or in the characteristics of milk fat dependent on the membrane.