Food Lipids: Chemistry, Nutrition, and Biotechnology

Table 1 13 C NMR Shifts for Allylic Carbons of Linoleic
Acid Geometric Isomers
Isomer
trans-9,trans-12 18:2
cis-9,trans-12 18:2
trans-9,cis-12 18:2
cis-9,cis-12 18:2
Source Ref. 39.
Chemical shift (ppm)
C11 C8 C14
35.7
30.5
30.55
25.75
32.60
27.15
32.60
27.35
32.60
32.60
27.60
27.35
[47]. This technique was also used to confirm the presence of specific trans diene
isomers in hydrogenated soybean oil [48].
The 13 C NMR signal from olefinic carbons yields bands that are indicative of
the double-bond position in unsaturated oils. Olefinic signals from 128 to 132 ppm
provide the most useful information about bond position [44]. Both signals obtained
for the two olefinic carbons in cis and trans monoene fatty acids, as well as their
differences, can be used to determine double-bond position.
D. FTIR–Partial Least Squares (PLS) Regression
To evaluate nutritional properties of foods, quantitative analysis of trans unsaturation
was investigated by using transmission FTIR–partial least squares (PLS) [49]. This
approach offered significantly reduced analysis time compared with conventional GC
methods and was effective for a wide range of trans values. Improved results were
reported for raw materials and food products [49].
A heated SB-HATR sampling accessory was developed and used to develop a
method for the simultaneous determination of iodine value (IV) and trans content
for neat fats and oils [50]. PLS regression was employed for the development of the
calibration models, and a set of nine pure triacylglycerol test samples served as the
calibration standards. Satisfactory agreement (SD < 0.35) was obtained between the
predictions from the PLS calibration model and trans determinations by the FTIR/
SB-HATR method.
E. Near-Infrared Spectroscopy
A generalized partial least squares calibration was developed for determination of
the trans content of edible fats and oils by Fourier transform near-infrared (FT-NIR)
spectroscopy [51]. The trans reference data, determined by using the SB-HATR mid-
IR official method, were used in the development of the generalized FT-NIR calibration.
The FT-NIR trans predictions obtained using this generalized calibration
were in good agreement with the SB-HATR results. The authors concluded that FT-
NIR provided a viable alternative to the SB-HATR [51].
III. ANALYSIS USING CHROMATOGRAPHY
The chromatography of lipids involves the separation of individual components of a
lipid mixture as they pass through a medium with a stationary matrix. This matrix
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.