Animal and vegetable fats and oils — Determination of the composition of fatty acids in the 2-position of the triglyceride molecules
1 Scope
This standard specifies a method for the determination of the composition of fatty acids which are esterified in the 2-position (ß or internal position) of the triglyceride molecules in animal and vegetable fats and oils.
Because of the nature of pancreatic lipase action, the method is applicable only to fats and oils with a melting point below 45 °C.
The method is not unreservedly applicable to all fats and oils, particularly those containing substantial amounts of
——fatty acids with 12 or fewer carbon atoms (e.g. copra oil, palm kernel oil, butyric butter fats);
——-fatty acids with 20 and more carbon atoms and of a high degree of unsaturation (more than four double bonds) (e.g. fish oil and marine animal oil);
——-fatty acids which have secondary groups containing oxygen.
Note: Fatty acids with double bonds in the (n-6) to (n-11) position (e.g. petroselinic acid) are converted only very slowly by pancreatic lipase. This may lead to wrong results.
2 Normative references
The following documents contain provisions which, through reference in this standard, constitute provisions of this standard. For dated references, subsequent amendments to, or revisions of, any of these publications (exclude errata) do not apply. However, parties of agreements based on this part of the directives are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the document referred to applies.
GB/T 5530 Animal and vegetable fats and oils - Determination of acid value and acidity (GB/T 5530-2005, ISO 660: 1996, IDT)
GB/T 6682 Water for analytical laboratory use - Specification and test methods (GB/T 6682-2008, ISO 3696: 1987, MOD)
GB/T 15687 Animal and vegetable fats and oils - preparation of test sample (GB/T 15687-2008, ISO 661: 2003, IDT)
GB/T 17376 Animal and vegetable fats and oils - Preparation of methyl esters of fatty acids (GB/T 17376-2008, ISO 5509: 2000, IDT)
GB/T 17377 Animal and vegetable fats and oils - Analysis by gas chromatography of methyl esters of fatty acids (GB/T 17377-2008, ISO 5508: 1990, IDT)
3 Principle
After neutralization, where necessary, of any free fatty acids, purification of the test portion by column chromatography. Partial enzymatic hydrolysis of the glycerides to yield 2-monoglycerides. Separation of the monoglycerides by thin-layer chromatography (TLC) and determination of their fatty acid composition by gas chromatography.
4 Reagents
Foreword I
1 Scope
2 Normative references
3 Principle
4 Reagents
5 Apparatus
6 Sampling
7 Preparation of test sample
8 Procedure
9 Expression of results
10 Precision
11 Test report
Annex A (Normative) Preparation of the lipase and checking its activity
Annex B (Informative) Results of interlaboratory tests
Bibliography
