Food Lipids: Chemistry, Nutrition, and Biotechnology

ucts were formed when aldehydes reacted with the amino group of the nitrogencontaining
phospholipid. Alternatively, antioxidant activity occurred when complexes
between peroxyl free radicals and the amino group were formed [104]. The latter
activity is supported by an extended induction period when both tocopherol and
phospholipids were present.
Fatty acid composition is a major factor affecting the susceptibility of a phospholipid
to assume an oxidized state, with carbon–hydrogen dissociation energies
decreasing as the number of bisallylic methylene positions increase [105,106]. However,
lipid unsaturation also physically affects oxidation. In model membrane bilayers
made from single unilamellar vesicles, lipid unsaturation resulted in smaller vesicles
and therefore a larger curvature of the outer bilayer leaflet. The increased lipid–lipid
spacing of these highly curved bilayers, in turn, facilitated penetration by oxidants
[107,108]. Other functional groups on the phospholipid will also impact their oxidative
stability. For example, the presence of an enol ether bond at position 1 of the
glycerol backbone in plasmalogen phospholipids has led to inhibition of lipid oxidation,
possibly through the binding of the enol ether double bond to initiating
peroxyl radicals [109]. Apparently, products of enol ether oxidation do not readily
propagate oxidation of polyunsaturated fatty acids. Alternatively, inhibition of lipid
oxidation by plasmalogens has been attributed to the iron binding properties of these
compounds [110]. Variation within the phospholipid classes toward oxidation has
also been ascribed to the iron trapping ability of the polar head group [111]. For
example, PS was shown to inhibit lipid peroxidation induced by a ferrous–ascorbate
system in the presence of PC hydroperoxides [112]. However, stimulation of phospholipid
oxidation by trivalent metal ions (Al 3� ,Sc 3� ,Ga 3� ,In 3� ,Be 2� ,Y 3� , and
La 3� ) has been attributed to the capacity of the ions to increase lipid packing and
promote the formation of rigid clusters or displacement to the gel state—processes
that bring phospholipid acyl chains closer together to favor propagation steps [113–
115].
XII. SUMMARY
This chapter has attempted to highlight the major chemical activities associated with
phospholipids and the relevance of these activities to the function of phospholipids
in foods. When present in oils or formulated floods, phospholipids may have either
detrimental or beneficial effects. As a major component of membranes, phospholipids
may also impact the quality of food tissues to a significant extent. Consequently,
their modifying presence should not be overlooked, even when they represent a small
proportion of the total lipid of a given food tissue.
REFERENCES
1. M. C. Moschidis. Phosphonolipids. Prog. Lipid Res. 23:223–246 (1985).
2. J. M. Seddon and G. Cevc. Lipid polymorphism: Structure and stability of lyotropic
mesophases of phospholipids. In: Phospholipids Handbook (G. Cevc, ed.). Dekker,
New York, 1993, pp. 403–454.
3. R. Fettiplace, I. G. H. Gordon, S. B. Hladky, J. Requens, H. B. Zingshen, and D. A.
Haydon. Techniques in the formation and examination of black lipid bilayer membranes.
In: Methods In Membrane Biology, Vol. 4 (E. D. Korn, ed.). Plenum Press,
New York, 1974, pp. 1–75.
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.