Handbook of Food Science and Technology 3

Partial coalescence occurs when fat globules, the fat of which is partially 
crystallized, aggregate but keep their shape after contact despite perforation of 
their membrane by lipid crystals. The mechanical rigidity provided by fat 
crystals on the surface of the fat globules prevents complete fusion. Partial 
coalescence is favored by the low interfacial tension and low viscoelasticity of 
the native MFGM.
Fats are also susceptible to biological (lipolysis) or chemical (oxidation) 
degradation. In fresh cow’s milk, lipolysis and oxidation of fat are virtually
non-existent despite the natural presence of lipoprotein lipase (lipolysis 
catalyst), oxygen and oxidation catalysts dissolved in the non-fat phase. The 
native MFGM, although relatively weak due to low interfacial tension (around 

---

18 Handbook of Food Science and Technology 3 
2 mN m
-1
) and the large radius of curvature, forms a protective layer against 
such reactions. However, any change to the native MFGM increases the risk of 
lipolysis and oxidation of milk fat.
1.2.1.2.
 Homogenized fat globules
Changing the physicochemical characteristics of an emulsion affects its 
properties. Homogenization, for example, improves the physical stability of 
emulsions by reducing the average diameter of the fat globules, and thus 
lowers the rate of creaming. The membrane becomes thicker and more 
viscoelastic due to the adsorption of casein micelles and whey proteins to the 
newly-formed interface (Figure 1.5); this limits the possibility of penetration 
of fat crystals and therefore reduces the risk of partial coalescence of the fat 
globules. However, the strong increase in the interfacial area and the change in 
the nature of the membrane due to homogenization alter its protective 
properties against oxidation and lipolysis.
Figure 1.5.
 Structure of the milk fat globule membrane after homogenization.
For a color version of this figure, see www.iste.co.uk/jeantet/foodscience.zip
In addition, homogenization changes the color of milk emulsions as well as 
the participation of fat globules in the formation of coagulum (cheese, 
yoghurt). Native fat globules cannot participate in the formation of the protein 
network. Moreover, if the diameter of the fat globules is greater than 1 µm, 
they even hinder the network formation. On the other hand, homogenized fat 
globules are involved in the formation of the protein network via the casein 
micelles incorporated into the interface created during homogenization. In 
low-fat products, homogenization (one stage) can be a means to increase the 
viscosity of dairy emulsions; in such systems, linear aggregates of flocculated 
fat globules are formed. Homogenization also causes an increase in the 
interfacial tension between the lipid and aqueous phases, which, together with 
Fragment of the 
native membrane
Whey proteins
Fragments of 
casein micelle
Casein micelle

---

From Milk to Dairy Products 19 
a reduction in fat globule size makes the interface more resistant to mechanical 
processing and phase inversion. Greater stability of fat globules resulting from 
changes to the interface may have an adverse effect on the rheological, sensory 
and culinary properties of cheese (altered melting properties after 
homogenization).