ISO 3657:2023
(Main)Animal and vegetable fats and oils — Determination of saponification value
Animal and vegetable fats and oils — Determination of saponification value
This document specifies a method for the determination of the saponification value of animal and vegetable fats and oils. The saponification value is a measure of the free and esterified acids present in fats and fatty acids. The method is applicable to refined and crude vegetable and animal fats. If mineral acids are present, the results given by this method are not interpretable unless the mineral acids are determined separately. The saponification value can also be calculated from fatty acid data obtained by gas chromatography analysis as given in Annex B. For this calculation, it is necessary to be sure that the sample does not contain major impurities or is thermally degraded.
Corps gras d'origines animale et végétale — Détermination de l'indice de saponification
Le présent document spécifie une méthode de détermination de l'indice de saponification des corps gras d’origines animale et végétale. L'indice de saponification est une caractéristique des acides gras libres et estérifiés présents dans les corps gras et acides gras. La méthode est applicable aux corps gras d'origines végétale et animale raffinés et bruts. En présence d'acides minéraux, les résultats donnés par cette méthode ne sont plus interprétables si l'on ne dose pas séparément l'acidité minérale. L’indice de saponification peut également être calculé à partir des données de composition en acides gras obtenues par chromatographie en phase gazeuse, selon l’Annexe B. Pour effectuer ce calcul, il est nécessaire de s’assurer que l’échantillon ne contient aucune impureté importante et qu’il n’est pas dégradé thermiquement.
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INTERNATIONAL ISO
STANDARD 3657
Sixth edition
2023-07
Animal and vegetable fats and oils —
Determination of saponification value
Corps gras d'origines animale et végétale — Détermination de l'indice
de saponification
Reference number
© ISO 2023
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Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 1
6 Apparatus . 2
7 Sampling . 2
8 Preparation of the test sample. 3
9 Procedure .3
9.1 Test portion . 3
9.2 Determination . 3
9.3 Blank test . 3
10 Expression of results . 3
11 Precision . 4
11.1 Results of interlaboratory test . 4
11.2 Repeatability . 4
11.3 Reproducibility . 4
12 Test report . 4
Annex A (informative) Results of the interlaboratory test . 5
Annex B (informative) Calculation of saponification value from fatty acid composition data .6
Bibliography .10
iii
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO’s adherence to
the 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, in collaboration with the European Committee for Standardization
(CEN) Technical Committee CEN/TC 307, Oilseeds, vegetable and animal fats and oils and their by-products
— Methods of sampling and analysis, in accordance with the Agreement on technical cooperation
between ISO and CEN (Vienna Agreement).
This sixth edition cancels and replaces the fifth edition (ISO 3657:2020), which has been technically
revised.
The main changes are as follows:
— errors in the calculations of the mean relative molecular mass (C16 TAG molecular weight) in B.7.4
and saponification value in B.7.5 have been corrected;
— incorrect values for the repeatability limit as well as the reproducibility limit values in Table A.1
have been corrected.
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
INTERNATIONAL STANDARD ISO 3657:2023(E)
Animal and vegetable fats and oils — Determination of
saponification value
1 Scope
This document specifies a method for the determination of the saponification value of animal and
vegetable fats and oils. The saponification value is a measure of the free and esterified acids present in
fats and fatty acids.
The method is applicable to refined and crude vegetable and animal fats.
If mineral acids are present, the results given by this method are not interpretable unless the mineral
acids are determined separately.
The saponification value can also be calculated from fatty acid data obtained by gas chromatography
analysis as given in Annex B. For this calculation, it is necessary to be sure that the sample does not
contain major impurities or is thermally degraded.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 661, Animal and vegetable fats and oils — Preparation of test sample
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
saponification value
I
s
number of milligrams of potassium hydroxide required for the saponification of 1 g of the product
tested
4 Principle
The test sample is saponified by boiling under reflux with an excess of ethanolic potassium hydroxide,
followed by titration of the excess potassium hydroxide with standard volumetric hydrochloric acid
solution.
5 Reagents
Use only reagents of recognized analytical grade, and distilled or demineralized water of equivalent
purity.
5.1 Ethanol, volume fraction φ = 95 %.
5.2 Potassium hydroxide, c(KOH) = 0,5 mol/l solution in ethanol.
This solution shall be colourless or straw yellow. A stable colourless solution can be prepared by either
of the following procedures:
a) Reflux 1 l of ethanol (5.1) with 8 g of potassium hydroxide and 5 g of aluminium pellets for 1 h, then
distil immediately. Dissolve the required amount of potassium hydroxide (approximately 35 g) in
the distillate. Allow to stand for several days, then decant the clear supernatant liquid from the
precipitated potassium carbonate into a brown-glass stock bottle.
b) Add 4 g of aluminium tert-butylate to 1 l of ethanol and allow the mixture to stand for several
days. Decant the supernatant liquid and dissolve in it the required amount of potassium hydroxide.
Allow to stand for several days, and then decant the clear supernatant liquid from the precipitated
potassium carbonate into a brown-glass stock bottle.
5.3 Hydrochloric acid, standard volumetric solution, c(HCl) = 0,5 mol/l.
5.4 Alkali blue 6B solution, ρ = 2,5 g/100 ml in ethanol (5.1).
5.5 Phenolphthalein solution, ρ = 0,1 g/100 ml in ethanol (5.1).
Phenolphthalein is classified as CMR substance and should only be used when no alternative is available.
5.6 Boiling aids.
6 Apparatus
Usual laboratory apparatus and, in particular, the following shall be used.
6.1 Conical flask, of 250 ml capacity, made of alkali-resistant glass and having a ground neck.
6.2 Reflux condenser, with a ground glass joint that fits the conical flask (6.1).
6.3 Heating device (e.g. a water-bath, electric hot-plate or other suitable apparatus). A naked flame
is not suitable.
6.4 Burette, capacity 50 ml, graduated in 0,1 ml divisions or automatic burette.
6.5 Pipette, capacity 25 ml or an automatic pipette.
6.6 Analytical balance, readability 0,000 1 g, weighing precision 0,001 g.
7 Sampling
Sampling is not part of this method specified in this document. A recommended sampling method is
given in ISO 5555.
It is important that the laboratory receive a truly representative sample that has not been damaged or
changed during transport or storage.
8 Preparation of the test sample
Prepare the test sample in accordance with ISO 661.
The test samples are carefully mixed and filtered if visible impurities are present. If filtration is
necessary, this shall be mentioned in the test report.
9 Procedure
9.1 Test portion
Weigh, to the nearest 5 mg, approximately 2 g of the test sample (see Clause 8) into a conical flask (6.1).
The test portion of 2 g has been determined on the basis of saponification values of 170 to 200. For other
saponification values, the mass should be altered accordingly so that approximately half the ethanolic
potassium hydroxide solution is neutralized. Recommendations for the mass of the test portion are
given in Table 1.
Table 1 — Mass of test portion
Expected saponification value Mass of test portion
g
150 to 200 2,2 to 1,8
200 to 250 1,7 to 1,4
250 to 300 1,3 to 1,2
> 300 1,1 to 1,0
9.2 Determination
9.2.1 Using a pipette (6.5), add to the test portion 25,0 ml of the ethanolic potassium hydroxide
solution (5.2) and some boiling aids (5.6). Connect the reflux condenser (6.2) to the flask, place the flask
on the heating device (6.3) and boil gently, shaking from time to time, for 1 h or for 2 h in the case of oils
and fats having a high melting point and which are difficult to saponify.
9.2.2 Add to the hot solution 0,5 ml to 1 ml of the colour indicator solution (5.4 or 5.5) and titrate
with the standard volumetric hydrochloric acid so
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