Pathogenic Microorganisms in Dairy Products


Dairy products are derived from a wide range of sources and a very popularity. Particularly, it has a high demand in vulnerable groups, like the infants, young children, pregnant women, elderly and some special care persons. If they consume the dairy products contaminated by pathogenic microorganisms, it may cause adverse health impacts and pose a high food safety risk.


Types of Dairy Products

In general, dairy products refer to foods made from animal milk as a basic ingredient, such as raw milk of cow or goat. According to the different processing methods, other ingredients or nutritional fortifiers are added to produce different types of dairy products, such as ultra-high temperature milk, pasteurised milk, modified milk, fermented milk, reconstituted milk and so on.


Heat treatment of dairy products

Dairy products are abundant in nutrients but they are susceptible to microbial contamination during the milk extraction. Therefore, raw milk that has not been sterilized by high-temperature cannot be consumed directly. In order to kill the pathogenic bacteria in raw milk and prolong its shelf life, dairy products are usually treated by 2 main sterilization methods, i.e., pasteurisation or ultra-high temperature processing (UHT). Please read the comparison table below for details.


Differences between Pasteurisation and Ultra-High Temperature (UHT) Sterilisation





Brief heating

(72℃ - 75℃ for 15 to 30 seconds)

Momentary heating at high temperatures

(135℃ - 150℃ for 2 to 3 seconds)



(Below 5℃)

Room temperature, avoid exposure to sunlight

(Refrigeration required once after packaging is opened)

Shelf life

6-10 days

6 months


Loss of partial nutrients*;

Retaining more natural flavour of milk

Loss of partial nutrients*;

Affecting the natural flavour of milk

* Thermo-sensitive nutrients (e.g. vitamin B1) are easily destroyed during the process of high temperature sterilisation.


Specification of the pathogenic microbial limits for dairy products in Macao

  The Administrative Regulation No. 2/2016 ‘Limits of Pathogenic Microorganisms in Dairy Products’ enacted in 2016 in Macao has expressly regulated the pathogenic microorganisms in dairy products. It is stipulated that Salmonella spp., Staphylococcus aureus and other coagulase-positive staphylococci and Listeria monocytogenes must not be detected in ultra-high temperature milk, pasteurised milk, modified milk and fermented milk. Moreover, in accordance with the existing laws, regulations and import regime of Macao, all milk and dairy products imported to Macao are required to submit a health certificate issued by exported competent authorities then are accepted mandatory inspection by Macao regulatory authorities before they enter the market for sale. In terms of market surveillance, dairy products are constantly examined in targeted food surveillance, which includes pathogenic microorganisms, harmful chemicals and nutrient components, so as to protect public health.


Why only regulated these 3 types of pathogenic microorganisms?

Salmonella spp., Staphylococcus aureus and other coagulase-positive staphylococci, as well as Listeria monocytogenes are identified as the high-risk pathogens in dairy products that cause foodborne diseases. They ought to be included in the food safety standards for specific control.


During the process of setting the standards, different referring aspects have been considered for safeguarding Macao food safety and protecting public health. References include the evaluation results of local risk surveillances, the standards and scientific findings from the risk assessment of pathogens established by relevant international organisations, the microbiological standards in food established by Codex Alimentarius Commission (CAC), the reports of the Joint FAO/WHO expert meetings on risk assessment of microbiological hazards related to food safety, the potential risks of microbiological hazard analysis by the International Commission on Microbiological Specifications for Foods (ICMSF), etc.


How should residents choose dairy products?

When choosing dairy products, consumers should patronise reputable and reliable shops in good hygiene condition. Pay attention to the expiry date and storage conditions shown on the food label. Do not buy any dairy product that has an abnormal appearance or unsealed packaging. Store the product properly according to its storage requirement. Once the dairy product is opened, consume it as soon as possible. If there is any doubt about the quality and hygiene condition of food, stop consuming it.