Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of ISO document should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

ISO draws attention to the possibility that the implementation of this document may involve the use of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s) which may be required to implement this document. However, implementers are cautioned that this may not represent the latest information, which may be obtained from the patent database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.

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

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 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/TS 11059 | IDF/RM 225:2009), which has been technically revised.

The main changes are as follows:

biochemical confirmation tests on oxidase reaction and glucose fermentation test have been aligned with the same confirmation tests used for presumptive Enterobacteriaceae;
the flow diagram in Annex A giving the main steps of the procedure has been added;
in Annex B, the criteria for the performance testing of culture media and reagents have been added.

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.

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.

IDF draws attention to the possibility that the implementation of this document may involve the use of (a) patent(s). IDF takes no position concerning the evidence, validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of this document, IDF had not received notice of (a) patent(s) which may be required to implement this document. However, implementers are cautioned that this may not represent the latest information, which may be obtained from the patent database available at www.iso.org/patents. IDF shall not be held responsible for identifying any or all such patent rights.

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

This document was prepared by IDF Standing Committee on Methods for Dairy Microbiology and ISO Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products. It is being published jointly by ISO and IDF.

The work was carried out by the IDF/ISO Action Team (H27) of the Standing Committee on Methods for Dairy Microbiology under the aegis of its project leader Julie Audy (CA).

Introduction

Pseudomonas spp. are aerobic, Gram-negative, non-spore-forming, flagellated, rod-shaped, catalase-positive bacteria. Pseudomonas spp. are a dominant group of psychrotrophic microorganisms associated with the contamination of raw or processed milk limiting the shelf life of fluid milk at 4 °C. The most important species causing spoilage in the dairy sector are from the P. fluorescens group including P. fluorescens, P. fragi and P. gessardii subgroups.

Pseudomonas spp. enter raw or processed milk from contaminated water or via biofilms in milking systems or process equipment. Pseudomonas spp. grow in raw or processed dairy products during refrigerated storage and some strains produce heat-stable extracellular enzymes (mainly lipases and proteases) causing a wide range of defects from off flavour to gelification (gelation) of ultra-high temperature (UHT) treated products. The enumeration of Pseudomonas spp. is used by the dairy sector as microbial indicator to evaluate raw milk quality or to determine a post-pasteurization contamination in processed milk from the milk-processing equipment.

This document is intended to provide general guidance for the examination of products not dealt with by existing International Standards and to be taken into account by organizations preparing microbiological test methods for application to milk and milk products and dairy environmental samples. This guidance will not always be appropriate in every detail for certain products, and for some other products it can be necessary to use different methods, see Reference [7]. Nevertheless, it is hoped that in all cases, every attempt will be made to apply the guidance provided as far as possible and that deviations from it will only be made if absolutely necessary for technical reasons.

The main technical changes listed in the Foreword, introduced in this document compared to ISO/TS 11059 | IDF/RM 225:2009, are considered as minor (see ISO 17468).

These technical changes have a minor impact on the performance characteristics of the method.

1 Scope

This document specifies the enumeration of Pseudomonas spp. by the colony-count technique.

This document is applicable to:

milk and milk products;
environmental samples in the area of dairy production and handling.

The method allows the isolation of all pigmented and non-pigmented psychrotrophic Pseudomonas spp.

2 Normative references

3 Terms and definitions

4 Principle

4.1 General

4.2 Preparation of dilutions

4.3 Enumeration

4.4 Confirmation

4.5 Calculation

5 Culture media and reagents

6 Equipment and consumables

6.1

6.2

6.3

6.4

6.5

6.6

6.7

6.8

6.9

6.10

6.11

7 Sampling

8 Preparation of test sample

9 Procedure

9.1 General

9.2 Test portion, initial suspension and dilutions

9.3 Inoculation and incubation

9.4 Counting and selection of colonies

9.5 Subculturing selected colonies

9.6 Confirmation

10 Expression of results

11 Test report

12 Quality assurance

Bibliography