Safeguarding Dairy Quality: A Deep Dive into ISO Standards for Microbial Enumeration in Milk and Milk Products

January 17, 2024 by
Safeguarding Dairy Quality: A Deep Dive into ISO Standards for Microbial Enumeration in Milk and Milk Products
Kadesha Dawkins


 The dairy industry faces ongoing challenges in maintaining the quality and safety of its products, with microbial contamination posing a significant risk to consumer health and brand integrity. This blog post delves into the critical role of ISO standards in enumerating specific microorganisms in milk, with a focus on the procedures outlined in ISO 11059:2009 for Pseudomonas spp. and ISO 11866-1:2005 for presumptive Escherichia coli.

Pseudomonas spp. Enumeration

 Background: Pseudomonas contamination in dairy products can lead to defects in taste, texture, and odor, potentially resulting in a loss of consumer trust. This issue often arises post-fermentation and calcium lactate production when the pH increases, creating favorable conditions for Pseudomonas growth.

Procedure Overview

 meticulously outlines the procedure for enumerating Pseudomonas spp. in milk and milk products. The process begins with sample preparation according to ISO 6887-5, followed by counting and selection of colonies from plates with 150 or fewer UFC (Unit Forming Colonies). The subsequent steps involve inoculation, incubation, and confirmation, with specific subcultures and tests to ensure accurate identification.


The bitter taste and rancid odor associated with Pseudomonas contamination make their detection crucial. ISO 11059:2009 provides a standardized approach to identifying and discarding contaminated products, thereby preserving both the sensory characteristics and safety of dairy goods.

Presumptive E. Coli Enumeration

Background: Escherichia coli, a diverse group of microorganisms, includes pathogenic strains that, when ingested, can lead to unspecific enterocolitis. ISO 11866-1:2005 addresses the necessity of enumerating presumptive E. Coli in milk and milk products, as it is one of the most common species associated with toxiinfections.

Procedure Overview

 In accordance with ISO 8261, ISO 11866-1:2005 details a method involving preparation, inoculation, incubation, and confirmation steps. This includes the use of double-strength modified Lauryl Sulfate Medium, enrichment medium, and various confirmatory tests such as gas formation and fluorescence checks.


 While E. Coli is more commonly found in raw milk, its survival through certain processing conditions mandates rigorous detection measures. ISO 11866-1:2005 ensures a systematic and reliable approach to identifying and managing E. Coli contamination, thereby safeguarding the safety of dairy products.

In the complex landscape of the dairy industry, ISO standards play a pivotal role in establishing clear and standardized procedures for microbial enumeration. Adhering to these standards not only ensures the safety of dairy products but also upholds the reputation and trustworthiness of dairy brands in the market. By implementing these detailed and meticulous procedures, the industry can continue to provide consumers with high-quality and safe dairy products while mitigating potential risks associated with microbial contamination.

Nutrient Agar 1060

Oxidase Reagent 6007

BCP Glucose Agar 1320

Kovac’s reagent 5205

Lauryl Sulphate Tryptose Broth Modified

REST Client (Huachao Mao)