Food Lipids: Chemistry, Nutrition, and Biotechnology

sibility of determining all components in a single analysis. The partial scanning and
redevelopment [126–128] that can be done with TLC-FID gives a unique advantage
over any other lipid analysis technique. TLC-FID system has been used to analyze
different types of lipids as detailed by Kaitaranta and Ke [129], Sebedio and Ackman
[130], Tanaka et al. [131], Walton et al. [132], Indrasena et al. [133], Kramer et al.
[134], Parrish et al. [135], and Przybylski and Eskin [136].
C. Spectroscopic Methods of Lipid Analysis
UV and visible spectroscopy are less frequently used but have specific applications
for the identification and quantification of lipids. IR spectroscopy was the first spectroscopic
method applied for the analysis of lipids. NMR and MS have been widely
used for lipid structure determination; however, new applications other than these
have been developed. IR, UV, and NMR are nondestructive spectroscopic methodologies.
1. UV-Visible Spectroscopy
UV and visible spectra of organic compounds are attributable to electronic excitations
or transitions. Functional groups with high electron density, such as carbonyl and
nitro groups with double, triple, or conjugated double bonds, absorb strongly in the
ultraviolet or visible range at characteristic wavelengths (� max) and molar extinction
coefficients (� max). Table 4 provides some of the diagnostic UV absorption bands for
lipid analysis. It should be noted that the � max for a compound may vary, depending
on the solvent used [83,84].
2. Infrared Absorption Spectroscopy
The IR spectrum of an oil provides substantial information on the structure and
functional groups of the lipid and also about the impurities associated with it. These
information are represented as peaks or shoulders of the spectrum as illustrated in
Figure 1. At the high frequency end of the spectrum (3700–3400 cm �1 ), there is a
Table 4 UV Absorption Characteristics of Some Chromophoric Groups
Chromophore Example � max (nm) � max Solvent
—C—C— Octene 177 12,600 Heptane
—C/C— Octyne 178
10,000
Heptane
196
2,100
—C—C—C—C— Butadiene 217 20,900 Hexane
—(C—C) n — Conjugated polyenes 217 � 30 (n � 2) 20,000–100,000 Hexane
C6H6 Benzene 184
47,000
Cyclohexane
202
7,000
255
230
—(C—C—C—C) n — �-Carotene 452
139,000 Hexane
478
12,200
HC—O Acetaldehyde 290 17 Hexane
C—O Acetone 275 17 Ethanol
—COOH Acetic to palmitic acid 208–210 32–50 Ethanol
Adapted from Ref. 83.
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.