Sources of microorganisms in food


Microorganisms are present in natural ecosystems such as air, soil and water. They are also present on the man himself and all living animals and plants. Therefore, all processed foods or can not be contaminated by microorganisms.

Contamination of food may have a more or less serious about product quality and consumer health. It can cause a deterioration of the product, making it lose its organoleptic characteristics and / or business; sometimes cause food-poisoning or serious infections.

The origin of the microorganisms found in foods depends on the one hand, the environment of the production of raw materials (soil, air, water) and on the other hand, requirements for its manipulation (crop or capture, transport, etc..) and processing (machinery, personnel, salaries of stabilization, etc..) in the finished product.

Initial contamination of raw material

The initial contamination of raw food is the product itself and the environment on which it was derived, namely water, soil and air.

Contamination of food by microorganisms in water

The water contains suspended diverse microbial load. The seeds are mostly water from the soil bacteria (Micrococcus, Pseudomonas, ...) or feces of human or animal (Enterobacteria, Enterococci, ...). These bacteria are often seeds of weathering and sometimes pathogenic to humans (Salmonella, Shigella, ...).

Molds such as Aspergillus, Penicillium, Fusarium, may also be present in water, and are often seeds of adulteration of food.

Yeasts, for against, are rarely encountered and therefore not involved in the contamination of food by microorganisms in the water.

The food of marine origin may be contaminated by germs from seawater (Aeromonas, Bacillus, Pseudomonas, ...). Usually these microorganisms are not pathogens. However, they can cause alterations in the fish after capture.

Contamination of food by soil microorganisms

Given the interaction between water and soil, found in the microorganisms have been cited for water. However, the importance of Clostridium among soil bacteria.

Products of plant origin (fruits, vegetables, etc..) Are most vulnerable to contamination by soil microorganisms. Contaminants can be transported by irrigation water, wind, insects and birds.

Contamination of food by microorganisms in the air

The air contains a large number of microbial cells. These are mostly bacteria, some fungi (Aspergillus, Alternaria, Penicillium, ...) and rarely yeasts.

Bacteria encountered in the air are the Micrococcus spore and bacteria, and pathogens are generally absent.

The most exposed to contamination by microorganisms in the air are those prepared in direct contact with air such as fruits, vegetables, meats, etc..

Contamination by microorganisms present on the products themselves

There are two types of microorganisms naturally present in food: the surface of microorganisms and the microorganisms in the digestive tract of animals.

Surface microorganisms food

Animals and plants contain live on their surface (skin of animals, plants envelopes, eggshells, etc.). An important microorganisms. Under normal conditions, this surface acts as a barrier to the penetration of germs inside products.

After the death of cells, the envelope no longer plays its role of protection because of the damage it has suffered, be it chemical, enzymatic or mechanical (cutting, grinding, pressing, etc.).. Thus, the products may be contaminated by microorganisms on their surface.

The feed can also be contaminated by microorganisms on teats. Similarly, damaged fruit and vegetables following harvest operations are contaminated by germs that are naturally on the surface.

Microorganisms found on the surface of foods are those usually encountered in soil, air and water. So these are bacteria (Micrococcus, Enterobacter, ...), molds (Aspergillus, Penicillium, Fusarium, ... ) and yeasts (Saccharomyces, ...).

Microorganisms in the digestive tract of animals

Microorganisms naturally present in the digestive system are usually bacteria such as Enterobacteria (Salmonella, Escherichia, Shigella, ...), enterococci (Streptococcus, ...) and other (Staphylococcus, Lactobacillus, ...). Molds are poorly represented among the yeasts, the genus Candida is the most common.

The viscera are the main sources of contamination of meat and fish. The contamination of muscle tissue is by migration of microorganisms through the lymphatic system and is facilitated by cutting and washing of carcasses.

Contamination of food by the plant and its environment

When performing the processing of food processing, these products are contaminated by microorganisms in the plant environment. Food products are again contaminated by germs from water, soil and air, plus other factors of contamination and that are unique to the plant (surfaces, equipment, utensils, personnel, etc. .).

These contaminants cause the diversity of the microbial flora found on food, but still specific to each product for the physico-chemical properties they own. These characteristics have a decisive role on the development or inhibition of such specific microbial flora.

Contamination by water

Besides its use as an ingredient in food preparation, water is used in several food processes: washing, fluid transport, cooling, cleaning and disinfection, etc..

When the water is of poor microbiological quality, it is an important source of food contamination. Water cooling, for example, is responsible for most of the contamination of sterilized cans, but badly crimped.

Contamination by air

The air is again an important source of contamination of foods that are handled in the open air. Air filtration and work under controlled atmosphere, reduces the contamination of food by microorganisms in the air.

Contamination by machinery and utensils

Machinery (grinders, mixers, etc..) And utensils (knives, etc..) Are also an important source of food contamination during preparation.

Germs carried by the equipment and utensils are generally the various contaminants of food. These bacteria multiply in the presence of food debris that remain adhered to the machines. That is why the plans for cleaning and disinfection of agro-industrial units should not be content with a superficial disinfection of equipment, but they must also provide for the dismantling of machinery and cleaning and disinfection of rooms, with sufficient frequency.

Contamination by staff

Contamination of foods during processing by staff is as important as the water contamination, air and machinery.

Microorganisms transmitted by staff are those that exist naturally in the human body or which may come from contaminated raw materials that the staff handles. Also, it is important to note that staff may be an important source of fecal contaminants (Escherichia, Staphylococcus, ...).

To control this type of contamination of food, it is essential that staff comply with good hygiene practices.


Microbial flora present in the finished product is the result of its history. The raw material has undergone several contaminations; initial contamination before it reaches the plant and another contamination during processing. The product has also undergone several treatments that have altered its physico-chemical treatment in addition to stabilization. All these treatments lead to a finished product with a specific microbial load.

The role of industrial agribusiness is to choose materials and processes that are appropriate so that the product is safe and complies with the requirements applicable to them.


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Very glad to see your blog, thank you share so many interesting things. Hope that in the future can see you day published more interesting! Can see your blog I very happy! Thanks for your sharing, I wish you a happy life!

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