EN ISO 8381:2000

SLOVENSKI STANDARD
SIST EN ISO 8381:2001
01-februar-2001
+UDQD]DPDMKQHRWURNHQDRVQRYLPOHND'RORþHYDQMHPDãþRE*UDYLPHWULMVND
PHWRGD5HIHUHQþQDPHWRGD,62
Milk-based infant foods - Determination of fat content - Gravimetric method (Reference
method) (ISO 8381:2000)
Säuglingsnahrung auf Milchbasis - Bestimmung des Fettgehaltes - Gravimetrisches
Verfahren (Referenzverfahren) (ISO 8381:2000)
Aliments a base de lait pour enfants en bas âge - Détermination de la teneur en matiere
grasse - Méthode gravimétrique (Méthode de référence) (ISO 8381:2000)
Ta slovenski standard je istoveten z: EN ISO 8381:2000
ICS:
67.100.99 'UXJLPOHþQLSURL]YRGL Other milk products
67.230 Predpakirana in pripravljena Prepackaged and prepared
hrana foods
SIST EN ISO 8381:2001 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 8381:2001

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SIST EN ISO 8381:2001

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SIST EN ISO 8381:2001

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SIST EN ISO 8381:2001
INTERNATIONAL ISO
STANDARD 8381
Second edition
2000-03-01
Milk-based infant foods — Determination of
fat content — Gravimetric method
(Reference method)
Aliments à base de lait pour enfants en bas âge — Détermination de la
teneur en matière grasse — Méthode gravimétrique (Méthode de
référence)
Reference number
ISO 8381:2000(E)
©
ISO 2000

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SIST EN ISO 8381:2001
ISO 8381:2000(E)
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ii © ISO 2000 – All rights reserved

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SIST EN ISO 8381:2001
ISO 8381:2000(E)
Contents Page
Foreword.iv
1 Scope .1
2 Normative reference .1
3 Term and definition .1
4 Principle.2
5 Reagents.2
6 Apparatus .2
7 Sampling.3
8 Preparation of test sample.4
8.1 Liquid products.4
8.2 Viscous or pasty products.4
8.3 Dried products .4
9 Procedure .4
9.1 Test portion .4
9.2 Blank tests.4
9.3 Preparation of fat-collecting vessel .5
9.4 Determination.5
10 Calculation and expression of results.7
10.1 Calculation.7
10.2 Expression of results .8
11 Precision.8
11.1 Interlaboratory test .8
11.2 Repeatability.8
11.3 Reproducibility.8
12 Test report .9
Annex A (informative) Notes on procedures.10
Annex B (informative) Alternative procedure using fat-extraction tubes with siphon or wash-bottle
fittings.12
Bibliography .15
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SIST EN ISO 8381:2001
ISO 8381:2000(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 8381 was prepared by Technical Committee ISO/TC 34, Agricultural food products,
Subcommittee SC 5, Milk and milk products, in collaboration with the International Dairy Federation (IDF) and
AOAC International, and will also be published by these organizations.
This second edition cancels and replaces the first edition (ISO 8381:1987), which has been technically revised.
Annexes A and B of this International Standard are for information only.
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SIST EN ISO 8381:2001
INTERNATIONAL STANDARD ISO 8381:2000(E)
Milk-based infant foods — Determination of fat content —
Gravimetric method (Reference method)
WARNING — The use of this International Standard may involve hazardous materials, operations and
equipment. This standard does not purport to address all the safety problems associated with its use. It is
the responsibility of the user of this standard to establish safety and health practices and determine the
applicability of regulatory limitations prior to use.
1 Scope
This International Standard specifies the reference method for the determination of the fat content of milk-based
infant foods.
The method is applicable to liquid, concentrated and dried milk-based infant foods with no, or not more than a mass
fraction of 5 % (dry matter) of starch or dextrin, or vegetable, fruit, meat, etc.
NOTE 1 Malto-dextrins without higher molecular mass dextrins, which are often present in infant foods, do not disturb the
Röse-Gottlieb extraction even when present in high concentrations.
The method is not applicable to products which do not dissolve completely in ammonia owing to the presence of
more than a few percent of starch or dextrin, or to the presence of hard lumps. The method is also not applicable to
products which contains free fatty acids in significant quantities. The results obtained for these products will be too
low.
NOTE 2 For such products, recourse should be made to a method utilizing the Weibull-Berntrop principle (see ISO 8262-1).
2 Normative reference
The following normative document contains provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, this publication do
not apply. However, parties to agreements based on this International Standard are encouraged to investigate the
possibility of applying the most recent editions of the normative document indicated below. For undated references,
the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of
currently valid International Standards.
ISO 3889, Milk and milk products — Determination of fat content — Mojonnier-type fat extraction flasks.
3 Term and definition
For the purposes of this International Standard, the following term and definition apply.
3.1
fatcontentofmilk
mass fraction of substances determined by the procedure specified in this International Standard
NOTE The fat content is expressed as a mass fraction, in percent [formerly given as % (m/m)].
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SIST EN ISO 8381:2001
ISO 8381:2000(E)
4 Principle
An ammoniacal ethanolic solution of a test portion is extracted with diethyl ether and light petroleum. The solvents
are removed by distillation or evaporation. The mass of the substances extracted is determined.
NOTE This is usually known as the Röse-Gottlieb principle.
5 Reagents
Use only reagents of recognized analytical grade, unless otherwise specified, and distilled or demineralized water or
water of equivalent purity.
The reagents shall leave no appreciable residue when the determination is carried out by the method specified (see
9.2.2).
5.1 Ammonia solution, containing a mass fraction of NH of approximately 25 % (� = 910 g/l).
3 20
NOTE If ammonia solution of this concentration is not available, a more concentrated solution of known concentration may
be used (see 9.4.2).
5.2 Ethanol (C H OH), or ethanol denatured by methanol, containing a volume fraction of ethanol of at least
2 5
94 %. (See A.5.)
5.3 Congo red solution
Dissolve1gof Congo red in water in a 100 ml one-mark volumetric flask (6.14). Dilute to the mark with water.
NOTE The use of this solution, which allows the interface between the solvent and aqueous layers to be seen more
clearly, is optional (see 9.4.4). Other aqueous colour solutions may be used provided that they do not affect the result of the
determination.
5.4 Diethyl ether (C H OC H ), free from peroxides (see A.3), containing no more than 2 mg/kg of antioxidants,
2 5 2 5
and complying with the requirements for the blank test (see 9.2.2, A.1 and A.4).
NOTE The use of diethyl ether could lead to hazardous situations. Due to expected changes in safety regulations studies
are ongoing to replace diethyl ether by another reagent provided that it does not affect the end result of the determination.
5.5 Light petroleum, with any boiling range between 30 °C and 60 °C or, as equivalent, pentane
(CH [CH ] CH ) with a boiling point of 36 °C and complying with the requirements for the blank test (see 9.2.2, A.1
3 2 3 3
and A.4).
NOTE The use of pentane is recommended because of its higher purity and constant quality.
5.6 Mixed solvent
Shortly before use, mix equal volumes of diethyl ether (5.4) and light petroleum (5.5).
6 Apparatus
WARNING — Since the determination involves the use of volatile flammable solvents, all electrical
apparatus employed shall comply with legislation relating to the hazards in using such solvents.
Usual laboratory equipment and, in particular, the following.
6.1 Analytical balance, capable of weighing to the nearest 1 mg, with a readability of 0,1 mg.
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SIST EN ISO 8381:2001
ISO 8381:2000(E)
6.2 Centrifuge, capable of holding the fat-extraction flasks or tubes (6.6) and capable of spinning at a rotational
–1 –1
frequency of 500 min to 600 min to produce a radial acceleration of 80 g to 90 g at the outer end of the flasks or
tubes.
NOTE The use of the centrifuge is optional but recommended (see 9.4.7).
6.3 Distillation or evaporation apparatus, for distilling the solvents and ethanol from the boiling or conical
flasks, or evaporating from beakers and dishes (see 9.4.14) at a temperature not exceeding 100 °C.
6.4 Drying oven, electrically heated, with ventilation port(s) fully open, capable of being maintained at a
temperature of 102 °C � 2 °C throughout its working space.
Theovenshallbefittedwithasuitablethermometer.
6.5 Water baths, capable of being maintained at temperatures of between 30 °C and 40 °C, 40 °C and 60 °C,
and 60 °C and 70 °C.
6.6 Mojonnier-type fat-extraction flasks, as specified in ISO 3889.
NOTE It is also possible to use fat-extraction tubes, with siphon or wash-bottle fittings, but then the procedure is different.
The alternative procedure is given in annex B.
The fat-extraction flasks shall be provided with good quality bark corks or stoppers of other material [e.g. silicone
rubber or polytetrafluoroethylene (PTFE)] unaffected by the reagents used. Bark corks shall be extracted with the
diethyl ether (5.4), kept in water at a temperature of 60 °C or more for at least 15 min, and shall then be allowed to
cool in the water so that they are saturated when used.
6.7 Rack, for holding the fat-extraction flasks (or tubes) (6.6).
6.8 Wash bottle, suitable for use with the mixed solvent (5.6).
A plastics wash bottle shall not be used.
6.9 Fat-collecting vessels, such as boiling flasks (flat-bottomed), of capacities 125 ml to 250 ml, conical flasks,
of capacity 250 ml, or metal dishes.
If metal dishes are used, they shall be of stainless steel, flat-bottomed with a diameter of 80 mm to 100 mm and a
height of approximately 50 mm.
6.10 Boiling aids, fat-free, of non-porous porcelain or silicon carbide (optional when metal dishes are used).
6.11 Measuring cylinders, of capacities 5 ml and 25 ml.
6.12 Pipettes, graduated, of capacity 10 ml.
6.13 Tongs, made of metal, for holding flasks, beakers or dishes.
6.14 Volumetric flask, one-mark, of capacity 100 ml.
7 Sampling
Sampling is not part of the method specified in this International Standard. A recommended sampling method is
given in ISO 707.
It is important that the laboratory receive a sample which is truly representative and has not been damaged or
changed during transport or storage.
Store all liquid, viscous or pasty samples at a temperature of between 2 °C and 6 °C from the time of sampling to
the time of commencing the procedure. In the case of samples in sealed cans or bottles, store these samples
unopened at a temperature below 20 °C.
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SIST EN ISO 8381:2001
ISO 8381:2000(E)
8 Preparation of test sample
8.1 Liquid products
Shake and invert the sample container. Open the container to pour the product slowly into a second sample
container provided with an airtight lid. Mix by repeated transfer the product, taking care to incorporate in the sample
any fat or other constituent adhering to the wall and ends of the first container. Transfer the test sample as
completely as possible to the second sample container. Close this container.
If necessary, condition the unopened sample container in the water bath (6.5) set at between 40 �C and 60 �C.
Remove and shake the container vigorously every 15 min. After 2 h, remove the container, dry the outside with a
tissue and allow to cool to room temperature. Remove the lid or cap entirely and thoroughly mix the contents by
stirring with a spoon or spatula. (If fat separates, do not test the sample.) Transfer the test sample as completely as
possible to a second sample container provided with an airtight lid. Close this container.
8.2 Viscous or pasty products
Open the sample container and thoroughly mix the contents with a spoon or spatula. If possible, use an up-and-
down rotary movement in such a way that the top layers and the contents of the lower corners of the container are
moved and mixed. Take care to incorporate in the test sample any fat or other constituents adhering to the wall and
ends of the container. Transfer the test sample as completely as possible to a second sample container provided
with an airtight lid. Close this container.
If necessary, condition the unopened sample container in the water bath (6.5) set at between 30 �C and 40 �C.
Remove the container, dry the outside with a tissue and open it. Scrape out all test sample adhering to the interior
of the container. Transfer the test sample to a dish large enough to permit thorough stirring, and mix until the whole
mass is homogeneous. Transfer the test sample as completely as possible to a second sample container provided
with an airtight lid. Close this container.
8.3 Dried products
Thoroughly mix the sample container by repeatedly rotating and inverting. If necessary, transfer all of the test
sample to a suitable airtight sample container of sufficient capacity to allow this operation to be carried out.
9 Procedure
NOTE 1 If it is required to check whether the repeatability limit (11.2) is met, carry out two single determinations in
accordance with 9.1 to 9.4.
NOTE 2 An alternative procedure using fat-extraction tubes with siphon or wash-bottle fittings (see note in 6.6) is given in
annex B.
9.1 Test portion
Mix the test sample (clause 8) in the case of viscous, pasty or dried products by stirring, or in the case of liquid
products by gently inverting the sample container three or four times. Immediately weigh to the nearest 1 mg,
directly or by difference, 1,5 g to 10 g of the test sample, corresponding to 1,0 to 1,5 g of dry matter, in a fat-
extraction flask (6.6).
Transfer the test portion as completely as possible into the lower (small) bulb of the fat-extraction flask.
9.2 Blank tests
9.2.1 Blank test for method
Carry out a blank test simultaneously with the determination using the same procedure and same reagents, but
replacing the dispersed test portion in 9.4.1 by 10 ml of water (see A.2).
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SIST EN ISO 8381:2001
ISO 8381:2000(E)
If the value obtained in the blank test regularly exceeds 1,0 mg, check the reagents if this has not been recently
done (9.2.2). Corrections of more than 2,5 mg should be mentioned in the test report.
9.2.2 Blank test for reagents
To test the quality of the reagents, carry out a blank test as specified in 9.2.1. Additionally use an empty fat-
collecting vessel, prepared as specified in 9.3, for mass control purposes. The reagents shall leave no residue
greater than 1,0 mg (see A.1).
If the residue of the complete reagent blank test is greater than 1,0 mg, determine the residue of the solvents
separately by distilling 100 ml of the diethyl ether (5.4) and light petroleum (5.5), respectively. Use an empty fat-
collecting vessel, prepared for control purposes as described above, to obtain the real mass of residue which shall
not exceed 1,0 mg.
Very occasionally, the solvents may contain volatile matter which is strongly retained in fat. If there are indications of
the presence of such substances, carry out blank tests on all the reagents and for each solvent using a fat-
collecting vessel with about 1 g of anhydrous butterfat. If necessary, redistil solvents in the presence of 1 g of
anhydrous butterfat per 100 ml of solvent. Use the solvents only shortly after the redistillation.
Replace unsatisfactory reagents and solvents, or redistil solvents.
9.3 Preparation of fat-collecting vessel
Dry a fat-collecting vessel (6.9) with a few boiling aids (6.10) in the oven (6.4) set at 102 °C for 1 h.
NOTE 1 Boiling aids are desirable to promote gentle boiling during the subsequent removal of solvents, especially when
using glass fat-collecting vessels; their use is optional with metal dishes.
Protect the fat-collecting vessel from dust and allow it to cool to the temperature of the weighing room (glass fat-
collecting vessel for at least 1 h, metal dish for at least 30 min).
NOTE 2 To avoid insufficient cooling or unduly long cooling times, the fat-collecting vessel should not be placed in a
desiccator.
Use tongs (6.13) to place the fat-collecting vessel on the balance. Weigh the fat-collecting vessel to the nearest
1,0 mg.
NOTE 3 Tongs should preferably be used to avoid, in particular, temperature variations.
9.4 Determination
9.4.1 Carry out the determination without delay.
If necessary, add preheated water at a temperature of 65 °C � 5 °C to the test portion in the fat-extraction flask (9.1)
to obtain a total volume of 10 ml to 11 ml. Use the water to wash the test portion on to the bottom of the flask.
Shake gently with slight warming in a water bath (6.5) set at between 40 °C and 60 °C until the test portion is
completely dispersed.
9.4.2 Add 2 ml of ammonia solution (5.1) to the dispersed test portion in the fat-extraction flask (9.4.1), or an
equivalent volume of a more concentrated ammonia solution (see note in 5.1). Mix thoroughly with the test portion in
the small bulb of the fat-extraction flask.
9.4.3 Heat the fat-extraction flask at 65 °C � 5 °C in the water bath (6.5) for 15 min to 20 min with occasional
shaking (optional in the case of liquid products). Cool in running water to room temperature.
9.4.4 Add 10 ml of ethanol (5.2). Mix gently but thoroughly by allowing the contents of the fat-extraction flask to
flow backwards and forwards between the small and large bulb. Avoid bringing the liquid too near to the neck of the
flask. If desired, add 2 drops of the Congo red solution (5.3). Cool in running water to room temperature.
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SIST EN ISO 8381:2001
ISO 8381:2000(E)
9.4.5 Add 25 ml of diethyl ether (5.4). Close the fat-extraction flask with a cork saturated with water or with a
stopper of other material wetted with water (6.6). Shake the flask vigorously, but not excessively, for 1 min to avoid
the formation of persistent emulsions.
While shaking, keep the fat-extraction flask in a horizontal position with the small bulb extending upwards,
periodically allowing the liquid to run from the large bulb into the small bulb. If necessary, cool the flask in running
water to about room temperature. Carefully remove the cork or stopper and rinse it and the neck of the flask with a
little mixed solvent (5.6). Use the wash bottle (6.8) so that the rinsings run into the flask.
9.4.6 Add 25 ml of the light petroleum (5.5). Close the fat-extraction flask with the rewetted (by dipping into water)
cork or stopper. Mix gently again for 30 s as described in 9.4.4. Proceed with shaking as described in 9.4.5.
9.4.7 Centrifuge the closed fat-extraction flask for between 1 min and 5 min at a radial acceleration of 80 g to
90 g. If a centrifuge (6.2) is not available, allow the closed flask to stand in the rack (6.7) for at least 30 min until the
supernatant layer is clear and distinctly separated from the aqueous layer. If necessary, cool the flask in running
water to room temperature.
9.4.8 Carefully remove the cork or stopper and rinse it and the inside of the neck of the fat-extraction flask with a
little mixed solvent (5.6). Use the wash bottle (6.8) so that the rinsings run into the flask. If the interface is below the
bottom of the stem of the flask, raise it slightly above this level by gently adding water down the side of the flask
(see Figure 1) to facilitate the decanting of solvent.
NOTE In Figures 1 and 2, one of the three types of fat-extraction flasks as specified in ISO 3889 has been chosen, but
this does not imply any preference over other types.
9.4.9 Hold the fat-extraction flask by the small bulb and carefully decant as much as possible of the supernatant
layer into the prepared fat-collecting vessel (see 9.3) containing a few boiling aids (6.10) in the case of a boiling or
conical flask (optional with metal dishes). Avoid decanting any of the aqueous layer (see Figure 2).
9.4.10 Rinse the outside of the neck of the fat-extraction flask with a little mixed solvent (5.6). Collect the rinsings
in the fat-collecting vessel. Take care that the mixed solvent does not spread over the outside of the fat-extraction
flask. If desired, remove the solvent or a part of it from the fat-collecting vessel by distillation or evaporation as
described in 9.4.14.
9.4.11 Add 5 ml of ethanol (5.2) to the contents of the fat-extraction flask. Using the ethanol, rinse the inside of the
neck of the flask and mix as described in 9.4.4.
9.4.12 Carry out a second extraction by repeating the operations described in 9.4.5 to 9.4.9 inclusive. Instead of
25 ml, use only 15 ml of diethyl ether (5.4) and 15 ml of light petroleum (5.5). Using the diethyl ether, rinse the inside
of the neck of the fat-extraction flask too.
If necessary, raise the interface slightly to the middle of the stem of the flask by gently adding water down the side
of the flask (see Figure 1) to enable the final decanting of solvent to be as complete as possible (see Figure 2).
9.4.13 Carry out a third extraction without addition of ethanol by again repeating the operations described in 9.4.5
to 9.4.9 inclusive. Again, use only 15 ml of diethyl ether (5.4) and 15 ml of light petroleum (5.5). Using the diethyl
ether, rinse the inside of the neck of the fat-extraction flask again.
If necessary, raise the interface slightly to the middle of the stem of the flask by gently adding water down the side
of the flask (see Figure 1) to enable the final decanting of solvent to be as complete as possible (see Figure 2).
NOTE The third extraction may be omitted for products with a fat content of less than 5 % (dry matter).
9.4.14 Remove the solvents (including the ethanol) as completely as possible from the fat-collecting vessel by
distillation if using a boiling or conical flask, or by evaporation if using a beaker or dish (6.3). Rinse the inside of the
neck of the conical flask with a little mixed solvent (5.6) before commencing the distillation.
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SIST EN ISO 8381:2001
ISO 8381:2000(E)
Key Key
1 Solvent 1 At second and third extraction
2 At second and third extraction 2 At first extraction
3 At first extraction 3 Aqueous layer
4 Interface 4 Interface
5 Aqueous layer
Figure 1 — Before decanting Figure 2 — After decanting
9.4.15 Heat the fat-collecting vessel, with the boiling or conical flask placed on its side to allow solvent
...