Milk - Quantitative determination of microbiological quality - Guidance for establishing and verifying a conversion relationship between results of an alternative method and anchor method results (ISO 21187:2021)

This document gives guidelines for the establishment of a conversion relationship between the results
of an alternative method and an anchor method, and its verification for the quantitative determination
of the microbiological quality of milk.
NOTE The conversion relationship can be used a) to convert results from an alternative method to the anchor
basis or b) to convert results/limits, expressed on an anchor basis, to results in units of an alternative method.

Milch - Quantitative Bestimmung der bakteriologischen Qualität - Leitfaden für die Erarbeitung einer Übertragungsbeziehung zwischen den Messwerten von Routine- und Bezugsverfahren sowie deren Verifizierung (ISO 21187:2021)

Dieses Dokument gibt Anweisungen für die Erarbeitung einer Übertragungsbeziehung zwischen den Ergebnissen eines alternativen und eines Bezugsverfahrens sowie für deren Verifizierung für die quantitative Bestimmung der mikrobiologischen Qualität von Milch.
ANMERKUNG   Die Übertragungsbeziehung kann a) zur Übertragung von Ergebnissen von einem alternativen Verfahren auf die Bezugsbasis oder b) zur Übertragung von Ergebnissen/Grenzwerten, ausgedrückt auf einer Bezugsbasis, in Ergebnisse in Einheiten eines alternativen Verfahrens verwendet werden.

Lait - Mesure quantitative de la qualité bactériologique - Lignes directrices pour établir et vérifier une relation de conversion entre les résultats de la méthode alternatif et les résultats de la méthode d'ancrage (ISO 21187:2021)

Le présent document donne des lignes directrices pour l'établissement d'une relation de conversion entre les résultats d'une méthode alternative et les résultats d'une méthode d'ancrage, et sa vérification en vue de la détermination quantitative de la qualité microbiologique du lait.
NOTE       La relation de conversion peut être utilisée a) pour convertir les résultats d'une méthode alternative sur la base de la méthode d'ancrage ou b) pour convertir les résultats/limites exprimés sur la base de la méthode d'ancrage, en résultats exprimés dans les unités d'une méthode alternative.

Mleko - Kvantitativno določanje bakteriološke kakovosti - Navodilo za ugotavljanje in preverjanje konverzijske povezave med rezultati alternativne metode in rezultati uveljavljene metode (ISO 21187:2021)

General Information

Status
Published
Public Enquiry End Date
04-Jul-2019
Publication Date
24-May-2021
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
22-Mar-2021
Due Date
27-May-2021
Completion Date
25-May-2021

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SLOVENSKI STANDARD
SIST EN ISO 21187:2021
01-julij-2021
Nadomešča:
SIST EN ISO 21187:2006

Mleko - Kvantitativno določanje bakteriološke kakovosti - Navodilo za ugotavljanje

in preverjanje konverzijske povezave med rezultati alternativne metode in rezultati

uveljavljene metode (ISO 21187:2021)

Milk - Quantitative determination of microbiological quality - Guidance for establishing

and verifying a conversion relationship between results of an alternative method and

anchor method results (ISO 21187:2021)

Milch - Quantitative Bestimmung der bakteriologischen Qualität - Leitfaden für die

Erarbeitung einer Übertragungsbeziehung zwischen den Messwerten von Routine- und
Bezugsverfahren sowie deren Verifizierung (ISO 21187:2021)

Lait - Mesure quantitative de la qualité bactériologique - Lignes directrices pour établir et

vérifier une relation de conversion entre les résultats de la méthode alternatif et les

résultats de la méthode d'ancrage (ISO 21187:2021)
Ta slovenski standard je istoveten z: EN ISO 21187:2021
ICS:
07.100.30 Mikrobiologija živil Food microbiology
67.100.10 Mleko in predelani mlečni Milk and processed milk
proizvodi products
SIST EN ISO 21187:2021 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 21187:2021
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SIST EN ISO 21187:2021
EN ISO 21187
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2021
EUROPÄISCHE NORM
ICS 07.100.30; 67.100.01 Supersedes EN ISO 21187:2005
English Version
Milk - Quantitative determination of microbiological
quality - Guidance for establishing and verifying a
conversion relationship between results of an alternative
method and anchor method results (ISO 21187:2021)

Lait - Mesure quantitative de la qualité Milch - Quantitative Bestimmung der bakteriologischen

microbiologique - Lignes directrices pour établir et Qualität - Leitfaden für die Erarbeitung einer

vérifier une relation de conversion entre les résultats Übertragungsbeziehung zwischen den Messwerten von

de la méthode alternatif et les résultats de la méthode Routine- und Bezugsverfahren sowie deren

d'ancrage (ISO 21187:2021) Verifizierung (ISO 21187:2021)
This European Standard was approved by CEN on 4 December 2020.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 21187:2021 E

worldwide for CEN national Members.
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SIST EN ISO 21187:2021
EN ISO 21187:2021 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO 21187:2021
EN ISO 21187:2021 (E)
European foreword

This document (EN ISO 21187:2021) has been prepared by Technical Committee ISO/TC 34 "Food

products" in collaboration with Technical Committee CEN/TC 302 “Milk and milk products - Methods of

sampling and analysis” the secretariat of which is held by NEN.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by September 2021, and conflicting national standards

shall be withdrawn at the latest by September 2021.

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

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN ISO 21187:2005.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,

Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of

North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the

United Kingdom.
Endorsement notice

The text of ISO 21187:2021 has been approved by CEN as EN ISO 21187:2021 without any modification.

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SIST EN ISO 21187:2021
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SIST EN ISO 21187:2021
INTERNATIONAL ISO
STANDARD 21187
IDF 196
Second edition
2021-02
Milk — Quantitative determination of
microbiological quality — Guidance
for establishing and verifying a
conversion relationship between
results of an alternative method and
anchor method results
Lait — Mesure quantitative de la qualité microbiologique — Lignes
directrices pour établir et vérifier une relation de conversion entre
les résultats de la méthode alternatif et les résultats de la méthode
d’ancrage
Reference numbers
ISO 21187:2021(E)
IDF 196:2021(E)
ISO and IDF 2021
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SIST EN ISO 21187:2021
ISO 21187:2021(E)
IDF 196:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO and IDF 2021

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

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office International Dairy Federation
CP 401 • Ch. de Blandonnet 8 Silver Building • Bd Auguste Reyers 70/B
CH-1214 Vernier, Geneva B-1030 Brussels
Phone: +41 22 749 01 11 Phone: +32 2 325 67 40
Fax: +32 2 325 67 41
Email: copyright@iso.org Email: info@fil-idf.org
Website: www.iso.org Website: www.fil-idf.org
Published in Switzerland
ii © ISO and IDF 2021 – All rights reserved
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SIST EN ISO 21187:2021
ISO 21187:2021(E)
IDF 196:2021(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ..............................................................................................................................................................................................................................vii

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

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

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

4 Principles ..................................................................................................................................................................................................................... 2

4.1 General ........................................................................................................................................................................................................... 2

4.2 Guidance for applied methods and laboratories ....................................................................................................... 2

4.3 Organizational set-up ........................................................................................................................................................................ 3

5 Consideration of factors influencing the conversion relationship ................................................................... 3

5.1 General ........................................................................................................................................................................................................... 3

5.2 Environmental factors ...................................................................................................................................................................... 3

5.2.1 General...................................................................................................................................................................................... 3

5.2.2 Animal species ................................................................................................................................................................... 4

5.2.3 Bulk milk storage conditions ................................................................................................................................. 4

5.2.4 Seasonal variations ........................................................................................................................................................ 4

5.2.5 Sampling and pre-treatment of the test samples ................................................................................. 4

5.2.6 Test sample preservation ......................................................................................................................................... 4

5.2.7 Milk production conditions .................................................................................................................................... 4

5.3 Analytical factors ................................................................................................................................................................................... 5

5.3.1 Instrument make and model ................................................................................................................................. 5

5.3.2 Chemicals ............................................................................................................................................................................... 5

5.3.3 High somatic cell counts ............................................................................................................................................ 5

6 Test samples .............................................................................................................................................................................................................. 5

6.1 Calculation of number of test samples ............................................................................................................................... 5

6.2 Range of test samples ........................................................................................................................................................................ 6

6.3 Representativeness of samples ................................................................................................................................................. 6

6.4 Pre-treatment of test samples ................................................................................................................................................... 6

6.4.1 General...................................................................................................................................................................................... 6

6.4.2 Preparation of sub-samples ................................................................................................................................... 6

6.4.3 Storage and transport of sub-samples .......................................................................................................... 7

7 Analysis .......................................................................................................................................................................................................................... 7

8 Establishing a conversion relationship ......................................................................................................................................... 7

8.1 General ........................................................................................................................................................................................................... 7

8.2 Validity of results .................................................................................................................................................................................. 7

8.3 Conversion relationship .................................................................................................................................................................. 8

8.4 Calculations ................................................................................................................................................................................................ 8

8.4.1 General...................................................................................................................................................................................... 8

8.4.2 Removal of outliers ........................................................................................................................................................ 8

8.4.3 Conversion relationship ............................................................................................................................................ 8

9 Verification of a conversion relationship .................................................................................................................................... 9

9.1 Frequency of verification ............................................................................................................................................................... 9

9.2 Calculation .................................................................................................................................................................................................. 9

10 Test report ................................................................................................................................................................................................................... 9

Annex A (informative) Number of test samples for linear regression............................................................................11

Annex B (informative) Example identification of outliers and calculation of conversion

relationship.............................................................................................................................................................................................................14

Annex C (informative) Example — Calculation of significance (verification of conversion

relationship) ..........................................................................................................................................................................................................15

© ISO and IDF 2021 – All rights reserved iii
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SIST EN ISO 21187:2021
ISO 21187:2021(E)
IDF 196:2021(E)

Bibliography .............................................................................................................................................................................................................................19

iv © ISO and IDF 2021 – All rights reserved
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SIST EN ISO 21187:2021
ISO 21187:2021(E)
IDF 196:2021(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).

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 5,

Milk and milk products, in collaboration with the European Committee for Standardization (CEN)

Technical Committee CEN/TC 302, Milk and milk products — Methods of sampling and analysis, in

accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement),

and the International Dairy Federation (IDF). It is being published jointly by ISO and IDF.

This second edition cancels and replaces the first edition (ISO 21187 | IDF 196:2004), which has been

technically revised. The main changes compared with the previous edition are as follows:

— the formula describing the conversion relationship has been based on grouped data rather than

data from individual samples;

— examples of how to perform outlier tests, and calculation and verification of conversion relationships

have been given in a spreadsheet.

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.
© ISO and IDF 2021 – All rights reserved v
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SIST EN ISO 21187:2021
ISO 21187:2021(E)
IDF 196:2021(E)

IDF (the International Dairy Federation) is a non-profit private sector organization representing the

interests of various stakeholders in dairying at the global level. IDF members are organized in National

Committees, which are national associations composed of representatives of dairy-related national

interest groups including dairy farmers, dairy processing industry, dairy suppliers, academics and

governments/food control authorities.

ISO and IDF collaborate closely on all matters of standardization relating to methods of analysis

and sampling for milk and milk products. Since 2001, ISO and IDF jointly publish their International

Standards using the logos and reference numbers of both organizations.

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

patent rights. IDF 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).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

This document was prepared by the IDF Standing Committee on Statistics and Automation and ISO

Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products. It is being

published jointly by IDF and ISO.

The work was carried out by the IDF/ISO Action Team (S11) of the Standing Committee on Statistics

and Automation under the aegis of its project leaders, Ms B. Asmussen (DK), Ms V. Tzeneva (NL), Mr R.

Kissling (NZ) and Ms B. Müller (DE).
vi © ISO and IDF 2021 – All rights reserved
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SIST EN ISO 21187:2021
ISO 21187:2021(E)
IDF 196:2021(E)
Introduction

Conversion in quantitative microbiology means expressing the result of a quantitative determination

of the microbiological status of a test sample obtained with an alternative method in units of another

method, generally an anchor method. Through this, quantitative results obtained with alternative

methods can be compared to values or limits that are stated in anchor method units. For establishing

and applying a conversion relationship, a number of prerequisites should be met. These are referred to

in this document, but are generally described elsewhere.

Although a considerable part of the applied principles for conversion coincides with those applied for

the calibration of indirect or alternative methods against an anchor method, or by means of (certified)

reference materials, it is stressed that the background and aims for applying conversion are different

from those for calibration. Calibration involves the determination of the adjustment needed for each

level of an analyte to closely approximate the true value of its concentration or number. However, in

quantitative microbiology, a true value in its strict sense cannot be established and is only defined by the

method description applied. When applying alternative methods in the quantitative determination of

microbiological quality, one is often dealing with different methodological principles and therefore also

other units. Conversion is used to transfer results obtained with different methods to a common scale.

© ISO and IDF 2021 – All rights reserved vii
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SIST EN ISO 21187:2021
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SIST EN ISO 21187:2021
ISO 21187:2021(E)
INTERNATIONAL STANDARD
IDF 196:2021(E)
Milk — Quantitative determination of microbiological
quality — Guidance for establishing and verifying a
conversion relationship between results of an alternative
method and anchor method results
1 Scope

This document gives guidelines for the establishment of a conversion relationship between the results

of an alternative method and an anchor method, and its verification for the quantitative determination

of the microbiological quality of milk.

NOTE The conversion relationship can be used a) to convert results from an alternative method to the anchor

basis or b) to convert results/limits, expressed on an anchor basis, to results in units of an alternative method.

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 8196-1 | IDF 128-1, Milk — Definition and evaluation of the overall accuracy of alternative methods of

milk analysis — Part 1: Analytical attributes of alternative methods

ISO 8196-2 | IDF 128-2, Milk — Definition and evaluation of the overall accuracy of alternative methods of

milk analysis — Part 2: Calibration and quality control in the dairy laboratory

ISO 16140-1, Microbiology of the food chain — Method validation — Part 1: Vocabulary

3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 8196-1 | IDF 128-1,

ISO 8196-2 | IDF 128-2, ISO 16140-1 and the following apply.

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/
3.1
alternative method

method of analysis allowing quantification of the microbiological status of a test sample

Note 1 to entry: The method can be proprietary or non-commercial.

Note 2 to entry: The term “alternative” in this document refers to the entire method. It includes all aspects (such

as test sample pre-treatment, materials and instruments) required for the execution of the method.

© ISO and IDF 2021 – All rights reserved 1
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SIST EN ISO 21187:2021
ISO 21187:2021(E)
IDF 196:2021(E)
3.2
anchor method

method of analysis internationally recognized by experts or by agreement between parties, and used,

for instance, in legislation when expressing official limits for microbiological quality

Note 1 to entry: It is stressed that, in quantitative microbiology, any obtained value is only defined by the method

description applied. This applies to any alternative method as well as, for instance, to the standard plate count

for the enumeration of microorganisms.
3.3
analyte
component or property which is measured by the method of analysis

Note 1 to entry: The analyte can be the microorganism, stained particles (e.g. microscopic count), components

of microorganisms (e.g. lipopolysaccharides), the result of their ability to multiply (e.g. colony-forming units) or

their metabolic activity (e.g. change in conductivity/impedance).
3.4
organizing body

organization, possibly appointed by a competent authority, having the qualified staff and skills to

organize, coordinate and report on the outcome of the activities for the establishment and/or the

maintenance of a conversion relationship
3.5
measuring range
range wherein data with known precision and accuracy can be obtained

Note 1 to entry: Precision and accuracy data are determined in a validation study (e.g. by the instrument

manufacturer or a responsible organization).
3.6
range of interest

numerical values for alternative method results, typical of routine samples when analysing in a

laboratory

Note 1 to entry: If applicable, the range of interest shall include official limits and limits related to specific quality

schemes.
4 Principles
4.1 General

The establishment and verification of a conversion relationship is based on the examination of test

samples with an alternative method and the anchor method.
4.2 Guidance for applied methods and laboratories

For establishing and verifying a conversion relationship between the results of an alternative method

and the anchor method, the following prerequisites apply.

The alternative method should have been evaluated and validated in accordance with ISO 16140-2

and/or ISO 16297 | IDF 161. Procedures for sampling, test sample preservation, test sample transport,

test sample storage, sample pre-treatment, analysis and calculation of results should be documented,

[6]

strictly standardized and controlled in agreement with ISO/IEC 17025, the Eurachem Guide or

comparable standards.

Regular participation in proficiency tests and training according to the relevant standards, e.g.

ISO 4833-1, ISO 14461-2 | IDF 169-2, is strongly recommended.
2 © ISO and IDF 2021 – All rights reserved
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SIST EN ISO 21187:2021
ISO 21187:2021(E)
IDF 196:2021(E)

The anchor method should have been validated, documented, strictly standardized and controlled in

agreement with ISO/IEC 17025, the Eurachem Guide or comparable standards.

The protocol for the establishment of the conversion relationship and its verification should be

documented. It should follow the guidelines of this document.
4.3 Organizational set-up

There are various possible organizational set-ups, e.g. both the alternative and the anchor method are

fully carried out in the same laboratory, or several laboratories are involved in the trial.

Due to the instability and variability of the microbiological status of milk samples, the most robust

conversion relationships will be obtained w
...

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