Food Lipids: Chemistry, Nutrition, and Biotechnology

determine the existing structural differences of fish oils and seal oil [160]. Phospholipase
A 2 is used to release fatty acids at the sn-2 position of the synthesized phosphatide
during the analytical procedure. Lands [161] used a different approach to
determine steric positions of the fatty acids. TAG is hydrolyzed with lipase and the
products are separated by TLC. The sn-3 hydroxyl of glycerol is phosphorylated with
diacylglycerol kinase to produce 3-phosphoryl monoacylglycerol. In the following
step of analysis, phospholipase A 2 is used to remove the fatty acids only from the
sn-2 position. The fatty acids in the sn-1 position can be released by saponifying the
resultant 1-acyl lysophosphatidic acid. The fatty acids in positions 1 and 2 can be
identified by GC analysis. The composition of fatty acids in position 3 can be calculated
by comparing these results with those from total fatty acid composition
determination of TAG.
E. Immunochemical Methods
Lipids are not generally very immunogenic. However, most glycolipids (except in
the pure form) possess antibodies of high activity and specificity. Therefore, glycolipids
to be administered to the animal are conjugated by covalent linking to a foreign
protein (as a hapten) or using them as a part of the bilayer of a liposome to stimulate
the production of specific antibodies [55,57]. Immunochemical methods have also
been developed for the assay of phospholipids and TAGs (55). The steroid hormones
when conjugated with serum albumin are sufficiently immunogenic to stimulate generation
of antibodies with high activity, and this allows their detection.
Immunostaining of TLC plates for detection and assay of glycoproteins is
widely done. The TLC chromatogram containing separated glycolipids is treated with
a radiolabeled specific antibody (usually with 125 I) to stain only the glycolipid antigen
even in the presence of overlapping glycolipids. Detection of 125 I may be achieved
using autoradiography, and the chromatographic mobility and antibody staining
serves to identify the glycolipid [84,92]. To overcome low sensitivity of the immunoradiolabeled
detection of glycolipids, enzyme-linked immunosorbent assay
(ELISA) was developed. For ELISA, lipid is usually bound to a solid phase and the
antibody is measured either by virtue of itself carrying enzyme or by using a second
antibody that carries an enzyme [84].
V. SUMMARY
Lipids are integral components and building blocks of biological materials. To understand
their constituents, chemistry, and biological functions, lipids have to be
isolated and studied. Therefore, an extensive knowledge of the extraction and analysis
of lipids is essential to carry out studies on lipids. This chapter provided comprehensive
information on methods available for extraction and analysis of lipids
from biological materials with examples when necessary. More details of a particular
topic could be obtained from the references listed.
REFERENCES
1. H. D. Belitz and W. Grosch. Food Chemistry. Springer-Verlag, New York, 1987.
2. D. E. Carpenter, J. N. Ngvainti, and S. Lee. Lipid analysis. In: Methods of Analysis
for Nutrition Labeling (D. M. Sulivan and D. E. Carpenter, eds.). AOAC Press, Arlington,
VA, 1993, pp. 85–104.
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.