chapter  2
Chemistry and Function of Phospholipids
Pages 24

I. Introduction ......................................................................................................................... 39 II. Phospholipid Classification ................................................................................................. 40 III. Phospholipid Physical Structures........................................................................................ 40 IV. Biological Membranes ........................................................................................................ 40

A. Membrane Properties .................................................................................................. 43 1. Membrane Permeability ....................................................................................... 43 2. Membrane Fluidity............................................................................................... 44 3. Phase Transitions ................................................................................................. 45 4. Heat Capacity ....................................................................................................... 46 5. Curvature=Stress=Surface Tension ....................................................................... 46

B. Fundamentals of Phospholipid Interactions ................................................................ 46 1. Complexation of Phospholipid to Ions ................................................................ 46 2. Phospholipid-Lipid Interactions .......................................................................... 47 3. Phospholipid-Protein Interactions ....................................................................... 48

C. Membrane Degradation............................................................................................... 49 V. Emulsifying Properties of Phospholipids............................................................................ 49 VI. Hydrolysis of Phospholipids ............................................................................................... 50

A. Chemical Hydrolysis ................................................................................................... 50 B. Enzymatic Hydrolysis ................................................................................................. 50

VII. Hydrogenation of Phospholipids......................................................................................... 51 VIII. Hydroxylation...................................................................................................................... 52 IX. Hydration ............................................................................................................................ 52 X. Oxidation............................................................................................................................. 53 XI. Summary ............................................................................................................................. 55

References ....................................................................................................................................... 55

Phospholipids can generally be regarded as fatty acyl-containing lipids with a phosphoric acid residue. Although hydrolysis is inherent to their ester and phosphoester bonds, other physical and chemical reactions associated with phospholipids are dictated by the kind of head group and by the chain length and degree of unsaturation of the constituent aliphatic groups. These activities constitute the focus of this chapter. In addition, the ramifications of the amphiphilic nature of phospholipids and their propensity to aggregate as bilayers and segregate into specific domains will be discussed in relation to their functional role in biological systems and foods.