Epicuticle composition

Leeder and Rippon [85] have analyzed the lipid composition of wool fibers after removing surface grease. Continued extraction with solvent removed the beta layers evidenced by electron microscopy however, the extract contained free cholesterol and free fatty acid and triglycerides but negligible quantities of phospholipid normally associated with biological membrane lipids. Koch [86], in his work with internal lipid of human hair, did not report significant quantities of phospholipid. These lipid-protein layers of hair are most likely related structurally to those of the epicuticle. 

The cuticle surface membrane contains a lipid and a proteinaceous component the term epicuticle is sometimes used to describe this surface membrane (Figure 5.5). However, it must be remembered that the epicuticle was originally defined as the membrane raised from the fiber surface. It is highly resistant and is raised as bubbles or saes from the underlying material after treatment with chlorine and water [50]. After isolation by agitation, as mentioned above, the epicuticle was shown to be predominantly proteinaceous [51]. Its similarity to cuticle composition led King and Bradbury to suggest that the isolated membrane consisted of multilayers derived from the fiber surface [49]. These authors also found lipids to be associated with the epicuticle. 

Wool fibers contain two types of cells, viz. cuticle cells and cortical cells. The cuticle cells consist of external epicuticle, exocuticle, and endocuticle. The cortical cells are divided into two different types of cells termed as orthocortical and paracortical cells which occupy about 90% of the wool fibers. They are separated from one another by a cell membrane complex with three layer structure. The cortex structure is constituted from the crystalline microfibril of the a-helical aggregate embedded in a matrix of high sulfur content. Wool fiber is thus a composite material with a variety of function on mechanical, chemical, and physical properties. 

---