oSIST prEN ISO 21187:2019

Milk - Quantitative determination of bacteriological quality - Guidance for establishing and verifying a conversion relationship between results of an alternative method and anchor method results (ISO/DIS 21187:2019)

Milch - Quantitative Bestimmung der bakteriologischen Qualität - Leitfaden für die Erarbeitung einer Übertragungsbeziehung zwischen den Messwerten von Routine- und Bezugsverfahren sowie deren Verifizierung (ISO/DIS 21187:2019)

Dieses Dokument gibt Anleitungen für die Erarbeitung einer Übertragungsbeziehung zwischen den Ergebnissen eines Alternativ- 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 Alternativverfahren auf die Bezugsbasis verwendet werden oder b) zur Übertragung von Ergebnissen/Grenzwerten, ausgedrückt auf einer Bezugsbasis, in Ergebnisse in Einheiten eines Alternativverfahrens;

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/DIS 21187:2019)

Mleko - Kvantitativno določanje bakteriološke kakovosti - Navodilo za ugotavljanje in preverjanje konverzijske povezave med rezultati alternativne metode in rezultati uveljavljene metode (ISO/DIS 21187:2019)

Standards Content (sample)

SLOVENSKI STANDARD
oSIST prEN ISO 21187:2019
01-julij-2019

Mleko - Kvantitativno določanje bakteriološke kakovosti - Navodilo za ugotavljanje

in preverjanje konverzijske povezave med rezultati alternativne metode in rezultati

uveljavljene metode (ISO/DIS 21187:2019)

Milk - Quantitative determination of bacteriological quality - Guidance for establishing

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

anchor method results (ISO/DIS 21187:2019)

Milch - Quantitative Bestimmung der bakteriologischen Qualität - Leitfaden für die

Erarbeitung einer Übertragungsbeziehung zwischen den Messwerten von Routine- und
Bezugsverfahren sowie deren Verifizierung (ISO/DIS 21187:2019)

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/DIS 21187:2019)
Ta slovenski standard je istoveten z: prEN ISO 21187
ICS:
07.100.30 Mikrobiologija živil Food microbiology
67.100.10 Mleko in predelani mlečni Milk and processed milk
proizvodi products
oSIST prEN ISO 21187:2019 en

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

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oSIST prEN ISO 21187:2019
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oSIST prEN ISO 21187:2019
DRAFT INTERNATIONAL STANDARD
ISO/DIS 21187
IDF 196
ISO/TC 34/SC 5 Secretariat: NEN
Voting begins on: Voting terminates on:
2019-04-02 2019-06-25
Milk — Quantitative determination of bacteriological
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 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

ICS: 67.100.01; 07.100.30
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference numbers
NATIONAL REGULATIONS.
ISO/DIS 21187:2019(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
IDF 196:2019(E)
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. ISO and IDF 2019
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oSIST prEN ISO 21187:2019
ISO/DIS 21187:2019(E)
IDF 196:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO and IDF 2019

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
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Published in Switzerland
ii © ISO and IDF 2019 – All rights reserved
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oSIST prEN ISO 21187:2019
ISO/DIS 21187:2019(E)
IDF 196:2019(E)
Contents Page

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

Introduction ................................................................................................................................................................................................................................vi

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

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

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

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

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

4.2 Requirements 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 Animal species ................................................................................................................................................................... 4

5.2.2 High somatic cell counts ............................................................................................................................................ 4

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

5.2.4 Sampling and pre-treatment of the samples ........................................................................................... 4

5.2.5 Test sample preservation ......................................................................................................................................... 4

5.2.6 Milk production conditions .................................................................................................................................... 4

5.2.7 Seasonal variations ........................................................................................................................................................ 4

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

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

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

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

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

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

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

6.4 Pretreatment 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 Calculation .................................................................................................................................................................................................. 7

8.1.1 General...................................................................................................................................................................................... 7

8.1.2 Validity of results ............................................................................................................................................................. 7

8.1.3 Removal of outliers ........................................................................................................................................................ 8

8.1.4 Conversion relationship ............................................................................................................................................ 8

8.1.5 Conversion equation ..................................................................................................................................................... 8

9 V erification of a conversion relationship .................................................................................................................................... 9

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

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

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

Annex A (informative) Number of samples for linear regression .......................................................................................10

Annex B (informative) Example – Identification of outliers and calculation of conversion

equation ......................................................................................................................................................................................................................13

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

relationship) ..........................................................................................................................................................................................................14

Bibliography .............................................................................................................................................................................................................................17

© ISO and IDF 2019 – All rights reserved iii
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oSIST prEN ISO 21187:2019
ISO/DIS 21187:2019(E)
IDF 196:2019(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 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.

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 and IDF 2019 – All rights reserved
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oSIST prEN ISO 21187:2019
ISO/DIS 21187:2019(E)
IDF 196:2019(E)
Foreword

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

worldwide. IDF membership comprises National Committees in every member country as well as

regional dairy associations having signed a formal agreement on cooperation with IDF. All members of

IDF have the right to be represented at the IDF Standing Committees carrying out the technical work.

IDF collaborates with ISO in the development of standard methods of analysis and sampling for milk

and milk products.

The main task of Standing Committees is to prepare International Standards. Draft International

Standards adopted by the Standing Committees are circulated to the National Committees for

endorsement prior to publication as an International Standard. Publication as an International Standard

requires approval by at least 50 % of IDF National Committees casting a vote.

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.

ISO 21187|IDF 169 was prepared by the International Dairy Federation (IDF) and Technical Committee

ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products. It is being published jointly by IDF

and ISO.

All work was carried out by the Joint ISO-IDF Actio Team (S11) of the Standing Committee on Statistics

and automation under the aegis of its project leaders, Mrs. B. Asmussen (DK), Mr. R. Kissling (NZ) and

Mrs. B. Müller (DE).
© ISO and IDF 2019 – All rights reserved v
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oSIST prEN ISO 21187:2019
ISO/DIS 21187:2019(E)
IDF 196:2019(E)
Introduction

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

of the bacteriological 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 International Standard, 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

bacteriological 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.

vi © ISO and IDF 2019 – All rights reserved
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oSIST prEN ISO 21187:2019
ISO/DIS 21187:2019(E)
DRAFT INTERNATIONAL STANDARD
IDF 196:2019(E)
Milk — Quantitative determination of bacteriological
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 (1) to convert results from an alternative method to the anchor

basis or (2) to convert results/limits, expressed on a 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 tht 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, Milk  —  Definition  and  evaluation  of  the  overall  accuracy  of  alternative  methods  of  milk

analysis — Part 1: Analytical attributes of alternative methods

ISO 8196-2, 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 11095, Linear calibration using reference materials

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

ISO 16140-2, Microbiology of the food chain — Method validation — Part 2: Protocol for the validation of

alternative (proprietary) methods against a reference method

ISO 16297, │IDF 161, Milk — Bacterial count — Protocol for the evaluation of alternative methods

3 Terms a nd definiti ons

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.
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 sample pretreatment, materials and instruments) required for the execution of the method.

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oSIST prEN ISO 21187:2019
ISO/DIS 21187:2019(E)
IDF 196:2019(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 may be the microorganism, stained particles (e.g. microsopic 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, to coordinate and to report on the outcome of the activities for the establishment of the

maintenane of a conversion relationship
3.5
measuring range

range in which reliable data can be obtained with an alternative method. Precision data for this

range were determined in a validation study (e.g. by the instrument manufacturer or a responsible

organization)
3.6
range of interest

numerical values in which the routine samples analysed in a laboratory can appear. This includes also

values which appear only infrequently. The range of interest also includes 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 an anchor method.
4.2 Requirements 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 according to ISO 16140-2 and/

or ISO 16297│IDF 161. Procedures for sampling, test sample preservation, sample transport, sample

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

standardized and controlled in agreement with ISO/IEC 17025, Eurachem Guide ‘Accreditation for

Microbiological Laboratories’ or comparable standards .

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

agreement with ISO/IEC 17025, Eurachem Guide ‘Accreditation for Microbiological Laboratories’ or

comparable standards .

1) Regular participation in proficiency tests and training according to the relevant standards, e.g. ISO 4833-1 and

ISO 14461│IDF 169, is strongly recommended.
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oSIST prEN ISO 21187:2019
ISO/DIS 21187:2019(E)
IDF 196:2019(E)

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

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

There are a number of situations which can be distinguished, 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 where the alternative method and the anchor method are

undertaken on the same test samples, at the same place, at the same time. It shall be ensured that either

the sequence of testing do not impose significant influence on the test results or the method with the

lowest influence on the milk sample is applied first.

Subsampling should be avoided. However, in case of two or more participating laboratories subsamples

may be necessary.

In all cases, the organizational set-up should include all the necessary provisions to guarantee that the

obtained conversion relationship is representative of the circumstances under which the alternative

method is carried out and the resulting conversion relationship is later applied. Factors to consider are

listed in Clause 5.

The organizing body should provide guidance to the collaborating laboratories. Furthermore, it should

collect information on critical points in the procedure. All collaborators should be asked to record

relevant information, such as details on the method(s) used, details on the testing of samples, quality

control data, and possibly data about storage and transport conditions.
5 Consideration of fa ctors influencing the conversion relationship
5.1 General

A number of factors can influence the outcome of alternative method or anchor method determinations,

or both. The relative magnitude of the effects can differ between test samples and is not necessarily

the same for both methods. This implies that certain factors can also influence the conversion

relationship. In the evaluation of an alternative method, all relevant factors should be identified and

should be considered since it is necessary to cover the consequences of their variation in one conversion

relationship, or otherwise to establish distinct conversion relationships.

In general, when distinction between samples cannot be made, or is not being made in routine

testing circumstances, the variation in the underlying variables should be covered in one conversion

relationship. Where a factor is shown to have a significant effect on the conversion relationship, more

than one conversion relationship may need to be established and applied.

Influencing factors are grouped into environmental factors affecting the milk sample e.g. content of

psychrotrophic bacteria or background noise from the sample matrix and analytical factors, which

relate to the analysis itself, e.g. reagents.

Below are listed some factors which can possibly influence the conversion relationship in raw milk

analysis. Some of these factors may be applied also to other situations.
5.2 Environmental factors

The microbiological flora of a milk sample, i. e. the type of microorganisms, their growth phase or

metabolic activity, influences the outcome of analytical methods depending on the principle of the

measurement and thus can have a significant impact on the conversion relationship. The normal

variation of microbiological flora should be included in a conversion relationship.

2) For example plate count method contrary to the flow-cytometric method counts only aerobic microorganisms

while anaerobic strains cannot be determined.
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oSIST prEN ISO 21187:2019
ISO/DIS 21187:2019(E)
IDF 196:2019(E)

Microorganisms in milk originate from the udder, the teat skin, from the air and from contamination

from feedstuff, milking equipment and containers. The number and type of bacteria in milk may depend

on the general characteristics of milk production such as the method of milking, storage conditions and

collection intervals. The growth phase is dependent on the sample handling. Thus, there are numerous

environmental factors influencing the microbiological flora of a milk sample. Some of these factors,

which should be considered in the organizational set-up of the trial, are listed below.

5.2.1 Animal species

Certain components in milk from different animal species such as cow versus goat may impact the

analytical results and thus influence the conversion relationship.

NOTE Influencing components may also originate from species-related aspects such as level of milk

production, applied milking technique etc.
5.2.2 High somatic cell counts

Elevated somatic cell counts (e.g. > 1 000 000 cells/ml) may cause increased background noise and

higher count values.
5.2.3 Bulk milk storage conditions

The storage and shipping conditions of the bulk milk will affect the number of bacteria and their growth

phase. When official limits are given dep
...