ISO/FDIS 23691
(Main)Microbiology of the food chain — Determination and use of cardinal values
Microbiology of the food chain — Determination and use of cardinal values
This document establishes basic principles and specifies requirements and methods to determine cardinal values of bacteria and yeast strains. These methods are based on (1) the determination of maximum specific growth rates of the studied strain grown in a defined range of values of the intrinsic or extrinsic factor under study and (2) on the use of secondary models to obtain the cardinal values. These methods can be applied to all type of bacteria and yeasts. Finally, this document provides guidelines on the use of the determined cardinal values in growth simulation based on predictive microbiological models.
Microbiologie de la chaîne alimentaire — Détermination et utilisation des valeurs cardinales
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FINAL DRAFT
International
Standard
ISO/TC 34/SC 9
Microbiology of the food chain —
Secretariat: AFNOR
Determination and use of cardinal
Voting begins on:
values
2025-08-25
Microbiologie de la chaîne alimentaire — Détermination et
Voting terminates on:
utilisation des valeurs cardinales
2025-10-20
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WITH THEIR COMMENTS, NOTIFICATION OF ANY
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INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 34/SC 9
Microbiology of the food chain —
Secretariat: AFNOR
Determination and use of
Voting begins on:
cardinal values
Microbiologie de la chaîne alimentaire — Détermination et
Voting terminates on:
utilisation des valeurs cardinales
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2025
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO
ISO/CEN PARALLEL PROCESSING
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland Reference number
ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 2
4 Principle . 6
4.1 General .6
4.2 Gamma functions .7
4.2.1 General .7
4.2.2 Describing effects of temperature .7
4.2.3 Describing effects of pH .8
4.2.4 Describing effects of a .9
w
4.2.5 Describing the effects of concentrations of inhibitors .10
4.3 Process of cardinal values and food correction factor determination .10
4.4 Determination of the maximum specific growth rate .11
4.4.1 General .11
4.4.2 Binary dilution OD-based method .11
4.4.3 Direct plating method . 12
4.5 Cardinal values determination . 13
4.6 Correction factor determination . 13
4.7 Validation .14
4.8 Use of cardinal values and food correction factor in predictions . 15
5 Reagents and materials .15
6 Apparatus . 16
7 Experimental design and data collection .16
7.1 General .16
7.2 Preparation of culture and medium .16
7.2.1 Choice and storage of studied strain .16
7.2.2 Preparation and inoculation of the microbial culture .17
7.2.3 Preparation of the modified nutrient broth .17
7.3 Levels per factor to estimate cardinal values .18
7.3.1 General .18
7.3.2 Temperature .19
7.3.3 pH . 20
7.3.4 Water activity.21
7.3.5 Inhibitory compounds . 22
7.4 Experimental design to estimate the maximum specific growth rate from the binary
dilution OD-based method . 22
7.5 Experimental design to estimate the maximum specific growth rate from the direct
plating method . 23
7.6 Determination of the food correction factor based on a challenge test . 23
7.7 Validation .24
8 Expression of the results: Estimation of the growth parameters .24
8.1 General .24
8.2 Assessment of maximum specific growth rate at each level of intrinsic or extrinsic
factors (first step) . 25
8.2.1 General . 25
8.2.2 Assessment of maximum specific growth rates from direct plating data . 25
8.2.3 Assessment of maximum specific growth rates by binary dilution OD-based
method . 25
iii
8.3 Assessment of cardinal values and optimum growth rate in broth, μ (second
Broth
step) .
8.3 Assessment of C (third step) . . 26
f
8.4 Validation (fourth step) .27
9 Use of cardinal values to perform microbial growth predictions .28
9.1 General . 28
9.2 Prerequisites for growth predictions . 28
9.3 Using cardinal values to simulate growth . 29
9.3.1 Growth simulation at a static given temperature . 29
9.3.2 Growth prediction with dynamic time-temperature scenario . 30
9.3.3 Growth simulation at a static condition of temperature, pH and a .31
w
10 Test report .33
11 Quality assurance .33
Annex A (informative) Indicative list of tools for primary and secondary fittings and
simulations.34
Annex B (informative) Guidance to obtain different a values when using different humectants
w
in broth .37
Annex C (infor
...
ISO/TC 34/SC 9/WG 19
Secretariat: AFNOR
Date: 2025-05-2708-11
Microbiology of the food chain — Determination and use of
cardinal values
FDIS stage
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
CP 401 • CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland.
ii
Contents
Foreword . v
Introduction. vi
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 2
4 Principle . 7
4.1 General . 7
4.2 Gamma functions . 8
4.2.1 General . 8
4.2.2 Describing effects of temperature . 8
4.2.3 Describing effects of pH . 9
4.2.4 Describing effects of aw . 9
4.2.5 Describing the effects of concentrations of inhibitors . 10
4.3 Process of cardinal values and food correction factor determination . 11
4.4 Determination of the maximum specific growth rate . 11
4.4.1 General . 11
4.4.2 Binary dilution OD-based method. 11
4.4.3 Direct plating method . 12
4.5 Cardinal values determination . 13
4.6 Correction factor determination . 14
4.7 Validation . 15
4.8 Use of cardinal values and food correction factor in predictions . 15
5 Reagents and materials . 16
6 Apparatus . 16
7 Experimental design and data collection . 17
7.1 General . 17
7.2 Preparation of culture and medium . 17
7.2.1 Choice and storage of studied strain . 17
7.2.2 Preparation and inoculation of the microbial culture . 18
7.2.3 Preparation of the modified nutrient broth . 18
7.3 Levels per factor to estimate cardinal values . 19
7.3.1 General . 19
7.3.2 Temperature . 20
7.3.3 pH . 21
7.3.4 Water activity . 22
7.3.5 Inhibitory compounds . 23
7.4 Experimental design to estimate the maximum specific growth rate from the binary
dilution OD-based method . 24
7.5 Experimental design to estimate the maximum specific growth rate from the direct
plating method . 24
7.6 Determination of the food correction factor based on a challenge test . 24
7.7 Validation . 25
8 Expression of the results: Estimation of the growth parameters . 26
8.1 General . 26
8.2 Assessment of maximum specific growth rate at each level of intrinsic or extrinsic
factors (first step) . 26
iii
8.2.1 General . 26
8.2.2 Assessment of maximum specific growth rates from direct plating data . 26
8.2.3 Assessment of maximum specific growth rates by binary dilution OD-based method . 26
8.3 Assessment of cardinal values and optimum growth rate in broth, µ (second
Broth
step) . 27
8.3 Assessment of C (third step) . 28
f
8.4 Validation (fourth step) . 28
9 Use of cardinal values to perform microbial growth predictions . 29
9.1 General . 29
9.2 Prerequisites for growth predictions . 29
9.3 Using cardinal values to simulate growth . 30
9.3.1 Growth simulation at a static given temperature . 30
9.3.2 Growth prediction with dynamic time-temperature scenario . 32
9.3.3 Growth simulation at a static condition of temperature, pH and aw . 32
10 Test report . 34
11 Quality assurance . 35
Annex A (informative) Indicative list of tools for primary and secondary fittings and
simulations . 36
Annex B (informative) Guidance to obtain different a values when using different
w
humectants in broth . 39
Annex C (informative) Growth rate determination . 40
Annex D (informative) Plate design . 44
Annex E (informative) Example of the use of cardinal values for growth simulation and its
variation . 45
Bibliography . 48
iv
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
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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
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This document was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 9,
Microbiology, in collaboration with the European Committee for Standardization (CEN) Technical
Committee CEN/TC 463, Microbiology of the food chain, in accordance with the Agreement on technical
cooperation between ISO and CEN (Vienna Agreement).
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.
v
Introduction
Under the general principles of the Codex Alimentarius on food hygiene, it is the responsibility of the food
business operators (FBOs) to control microbiological hazards in foods and to manage microbial risks.
Therefore, it is the responsibility of the FBO to implement validated control measures, within the hazard
analysis and critical control point (HACCP) system, and conduct studies in order to investigate
compliance with the food safety
...
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