Nutrition Science and Everyday Application - beta v 0.1

LIPID TYPES AND STRUCTURES 263
Figure 5.10. The phospholipid bilayer consists of two adjacent sheets of phospholipids, arranged
tail to tail. The hydrophobic tails associate with one another, forming the interior of the
membrane. The polar heads contact the fluid inside and outside of the cell.
Another important role of phospholipids is to act as emulsifiers. Emulsions are mixtures of
two liquids that do not normally mix (oil and water, for example). Without an emulsifier, the
oil and water separate out into two layers. Because of their ability to mix with both water
and fat, phospholipids are ideal emulsifiers that can keep oil and water mixed, dispersing
tiny oil droplets throughout the water. Lecithin—a phospholipid found in egg yolk, soybean,
and wheat germ—is often used as a food emulsifier. Emulsifiers also play an important
role in making food appetizing; their inclusion in foods like sauces and creams makes for a
smoother texture and prevents the oil and water ingredients from separating out. They also
can extend shelf life.