Vegetable fats and oils — Determination of composition of triacylglycerols and composition and content of diacylglycerols by capillary gas chromatography

This document specifies the determination of composition of triacylglycerols and the determination of the composition and content of diacylglycerols by capillary gas chromatography in vegetable oils with a lauric acid content below 1 %. Applying certain technological processing 1,2-diacylglycerols (1,2-DAGs) are transformed to the more stable isomeric 1,3-diacylglycerols (1,3-DAGs) due to acidic catalysed reaction. During storage, the speed and amount of this rearrangement depends on the acidity of the oil. The transformation normally reaches an equilibrium between the two isomeric forms. The relative amount of 1,2-DAGs is related to oil freshness or to a possible technological treatment. Therefore, it is possible to use the ratio of 1,2-DAGs to 1,3-DAGs as a quality criterion for vegetable fats and oils. The triacylglycerols profile is of potential interest for the fingerprint of each vegetable oil and may help the detection of certain types of adulteration, such as the addition of high oleic sunflower oil or palm olein in olive oil. NOTE This document is based on Reference [3].

Corps gras d'origine végétale — Détermination de la composition des triacylglycérols et de la teneur en diacylglycérols par chromatographie en phase gazeuse sur colonne capillaire, dans les huiles végétales

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Status
Published
Publication Date
06-Aug-2018
Current Stage
6060 - International Standard published
Start Date
07-Aug-2018
Completion Date
07-Aug-2018
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INTERNATIONAL ISO
STANDARD 21846
First edition
2018-08
Vegetable fats and oils —
Determination of composition of
triacylglycerols and composition and
content of diacylglycerols by capillary
gas chromatography
Corps gras d'origine végétale — Détermination de la composition
des triacylglycérols et de la teneur en diacylglycérols par
chromatographie en phase gazeuse sur colonne capillaire, dans les
huiles végétales
Reference number
ISO 21846:2018(E)
ISO 2018
---------------------- Page: 1 ----------------------
ISO 21846:2018(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2018

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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Published in Switzerland
ii © ISO 2018 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 21846:2018(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 1

5 Apparatus ..................................................................................................................................................................................................................... 2

6 Reagents ........................................................................................................................................................................................................................ 2

7 Procedure..................................................................................................................................................................................................................... 3

7.1 Gas chromatographic apparatus and capillary column condition .............................................................. 3

7.2 Choice of operating conditions ................................................................................................................................................. 3

7.3 Performance of the analysis ........................................................................................................................................................ 3

7.4 Peak identification ............................................................................................................................................................................... 3

7.5 Determination of percentage content of each triacylglycerol class ........................................................... 4

7.6 Determination of percentage content of each 1,2 diacylglycerol ................................................................ 4

7.7 Determination of weight percentage total content of diacylglycerols .................................................... 4

8 Expression of results ........................................................................................................................................................................................ 5

9 Precision of the method ................................................................................................................................................................................ 5

9.1 Repeatability, r .........................................................................................................................................................................................5

9.2 Reproducibility, R ...................................................................................................................................................................................5

10 Test report ................................................................................................................................................................................................................... 5

Annex A (informative) Examples of a typical chromatograms .................................................................................................. 6

Annex B (informative) Results of an interlaboratory test ...........................................................................................................11

Bibliography .............................................................................................................................................................................................................................13

© ISO 2018 – All rights reserved iii
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ISO 21846:2018(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/patents).

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World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso

.org/iso/foreword .html.

This document was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 11,

Animal and vegetable fats and oils.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2018 – All rights reserved
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INTERNATIONAL STANDARD ISO 21846:2018(E)
Vegetable fats and oils — Determination of composition
of triacylglycerols and composition and content of
diacylglycerols by capillary gas chromatography
1 Scope

This document specifies the determination of composition of triacylglycerols and the determination of

the composition and content of diacylglycerols by capillary gas chromatography in vegetable oils with

a lauric acid content below 1 %.

Applying certain technological processing 1,2-diacylglycerols (1,2-DAGs) are transformed to the more

stable isomeric 1,3-diacylglycerols (1,3-DAGs) due to acidic catalysed reaction. During storage, the

speed and amount of this rearrangement depends on the acidity of the oil. The transformation normally

reaches an equilibrium between the two isomeric forms. The relative amount of 1,2-DAGs is related to

oil freshness or to a possible technological treatment. Therefore, it is possible to use the ratio of 1,2-

DAGs to 1,3-DAGs as a quality criterion for vegetable fats and oils.

The triacylglycerols profile is of potential interest for the fingerprint of each vegetable oil and may help

the detection of certain types of adulteration, such as the addition of high oleic sunflower oil or palm

olein in olive oil.
NOTE This document is based on Reference [3].
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
4 Principle

After the addition of an internal standard the oil sample is silylated, dissolved in a suitable reagent and

directly injected in the gas chromatographic apparatus. Triacyglycerols are separated into classes on

the basis of their carbon atom number, while diacylglycerols are separated in function of their carbon

atom number and structure, as 1,2 structures show a lower retention time than 1,3 ones.

Unsaturated diacylglycerol structures do not affect retention time. Therefore, saturated and

unsaturated diacylglycerols elute together, so 1,2 and 1,3-diacylglycerol structures are identified by

their peak retention time. The percentage content of 1,2 structure is determined through the ratio of

1,2-diacylglycerol areas to the sum of areas of all the diacylglycerol peaks.
The diacylglycerol total content is calculated by means of an internal standard.

The percentage content for each triacylglycerol class is calculated after normalization to 100 % of all

the triacylglycerol peaks.
© ISO 2018 – All rights reserved 1
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ISO 21846:2018(E)
5 Apparatus

5.1 Analytical balance suitable to perform weighing to an accuracy of within +/−0,1 mg.

5.2 Gas chromatograph for use with a capillary column, equipped with a system for direct on-column

for cold injection or a programmed temperature vaporizer.
5.3 Thermostat-controlled oven with temperature programming.
5.4 Cold injector for on-column injection or programmed temperature vaporizer.
5.5 Flame-ionization detector and converter-amplifier.

5.6 Recorder-integrator for use with the converter-amplifier (5.5), with a rate of response below 1 s

and variable paper speed, or any suitable device for data capture and handling.

5.7 Capillary column, fused silica, 6 m to 8 m length, 0,25 mm to 0,32 mm internal diameter,

internally coated with SE 52, SE 54 liquid phase to a uniform thickness of 0,10 μm to 0,15 μm.

5.8 Microsyringe, 10 μl, with a hardened needle for on-column injector.
5.9 Microsyringe, 100 μl, with a hardened needle.
5.10 Usual laboratory glassware.
6 Reagents

WARNING — Attention is drawn to the regulations which specify the handling of hazardous

substances. Technical, organizational and personal safety measures shall be followed.

Unless otherwise stated analytically pure reagents shall be used.
6.1 Carrier gas: hydrogen or helium, pure, for gas chromatography.
6.2 Auxiliary gases:
— hydrogen, pure, for gas chromatography;
— air, pure, for gas chromatography.
6.3 Silylating reagent, mix equal volumes of
— pyridine, and
— bistrimethy
...

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