Food Emulsifiers and Stabilizers - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 210

foams. Emulsions in creams, ice creams, toppings, and other desserts are invariably
stabilized by milk proteins. Stabilization of emulsion droplets by milk proteins has
been discussed in a series of publications by Walstra and co-workers. 25,26 It is usually
casein, often in aggregated form, which acts as the main stabilizer. In protein-based
emulsions, the ability of droplets to coalesce can be almost infinite. Perversely, the
functional requirements of practical food emulsions are not for complete stability,
but rather for controlled instability. Thus, a cream must be stable during production
and distribution, but must destabilize during whipping. This may be achieved by
displacing protein from the interface by the addition of a second (low molecular
weight) surfactant, or by controlling fat crystallization such that crystals bridge the
interfacial protein membrane. 27

Liquid-Crystalline Phases and Emulsion Stability

An important concept in the understanding of emulsions stabilized by polar lipids
is the thermodynamic phase equilibria of the corresponding ternary system:
oil-water-surfactant, which was first introduced by Larsen and Friberg. 4 It was
demonstrated that a maximum in emulsion stability is obtained when three phases
exist in equilibrium, and it was therefore proposed that the lamellar liquid-crystalline
phase stabilize the emulsion by forming a film at the oil-water interface. As shown
in Figure 7.1 , the lamellar-crystalline phase can exhibit a hydrophobic surface toward

Palissade layer

H 2

H 2

Oil (1)

H 2

H 2

Oil (2)

FIGURE 7.1 Schematic representation of the interfacial region of an L 2 droplet (containing
oil 1; dispersed in oil 2). (From Hernquist, L., Polar Lipids in Emulsions, in Food Emulsions
and Foams, Dickenson, E., Ed., Royal Society of Chemistry, London, 1987. With permission.)