176 3 Lipids
Alternatively, the stereo-specific analysis can be
carried out chemically. The TGs are partially
hydrolyzed in the presence of ethyl magne-
sium bromide. The resulting diacylglycerols
are isolated and their OH groups converted to
urethane with (S)-1-(1-naphthyl)ethylisocyanate.
The sn-1,3- and the diastereomeric sn-1,2-
and 2,3-di-acylglycerol urethane derivatives
are separated in a subsequent HPLC step. The
fatty acid analysis of the urethanes show the
distribution of the acyl residues in positions 1, 2
and 3.
Individual TGs or their mixtures can be analyzed
with these procedures. Based on these results
(some are presented in Table 3.16), general rules
for fatty acid distribution in plant oils or fats can
be deduced:
- The primary HO-groups in positions 1 and 3 of
glycerol are preferentially esterified with satu-
rated acids. - Oleic and linolenic acids are equally dis-
tributed in all positions, with some exceptions,
such as cocoa butter (cf. Table 3.16). - The remaining free position, 2, is then filled
with linoleic acid.
Table 3.16.Results of stereospecific analysis of some fats and oilsa
Fat/Oil Position 16:0 18:0 18:1 (9) 18:2 (9,12) 18:3 (9,12,15)
Peanut 1 13. 64. 659. 218 .5–
21. 60. 358. 538 .6–
311. 05. 157. 318 .0–
Soya 1 13. 85. 922. 948. 49. 1
20. 90. 321. 569. 77. 1
313. 15. 628. 045. 28. 4
Sun- 1 10. 63. 316. 669 .5–
flower 2 1. 31. 121. 576 .0–
39. 79. 227. 653 .5–
Olive 1 15. 22. 968. 611 .0–
22. 50. 681. 014 .6–
319. 65. 262. 69 .4–
Palm 1 60. 13. 426. 89 .3–
213. 30. 267. 917 .5–
371. 97. 614. 43 .2–
Cocoa 1 34. 050. 412. 31 .3–
21. 72. 187. 48 .6–
336. 552. 88. 60 .4–
Chicken 1 68. 26. 012. 42 .3–
egg 2 4. 80. 360. 831 .3–
38. 97. 769. 45 .4–
aValues in mol%. In order to simplify the Table other fatty acids present in fat/oil are not listed.
Results compiled in Table 3.16 show that for
oil or fat of plant origin, the difference in acyl
residues between positions 1 and 3 is not as great
as for TGs of animal origin (e. g., chicken egg).
Therefore, the 1,3-random-2-random hypothesis
can provide results that agree well with experi-
mental findings.
The fatty acid pattern in animal fats is strongly
influenced by the fatty acid composition of ani-
mal feed. A steady state is established only after
4–6 months of feeding with the same feed compo-
sition. The example of chicken egg (Table 3.16)
indicates that positions 1 and 3 in triglycerides
of animal origin show much greater variability
than in fats or oils of plant origin. Therefore, any
prediction of TG types in animal fat should be
calculated from three separate fatty acid pools
(1-random-2-random-3-randomhypothesis).
The specific distribution of saturated fatty acids
in the triglycerols of fats and oils of plant origin
serves as an evidence ofester oils.
Ester oils are produced by esterification of
glycerol with purified fatty acids obtained from
olive oil residues. In this case the saturated acyl
groups are equally distributed between all three
positions of the glycerol molecule, whereas