Microorganisms in food

Overview

Microorganisms are important food microbial germs found associated with foods. These are either the seeds of initial contamination of raw materials or contaminants due to handling and processing of such material, or microorganisms deliberately added for a technological purpose (in the case of lactic bacteria for example). The different sources of microbial contamination of food is discussed in another paper: "Origin of microorganisms in food."

The importance of food microorganisms are represented primarily by four groups: bacteria, yeasts, molds and viruses.

Bacteria

Among all the existing microorganisms, the bacteria that pose the greatest difficulty in preserving food. Most bacteria are relatively harmless, but they secrete enzymes capable of altering food. In some cases, bacteria can produce toxic substances.

Among thirty bacterial genera encountered on food, the most important are Escherichia, Salmonella, Pseudomonas, Bacillus, Clostridium, Lactobacillus and Staphylococcus. Some species such as Salmonella typhi, Staphylococcus aureus and Clostridium botulinum are pathogenic. Table 1 following lists the main bacterial genera encountered in foods.

Yeast

Widespread in nature, particularly affect yeast acidic, sweet, salty or high in fat. They tolerate the cold better than heat, most yeasts are destroyed from 77 ° C.

Most yeasts encountered in food belong to the families of Saccharomycetaceae and Crytococcaceae. Table 2 below lists the main types of yeast found in foods.

In general, yeasts are not pathogenic. But their presence in foods is often undesirable because of deterioration that can result.

Mold

The molds are widespread in nature and are common in soil and dust in the air. When moisture conditions, aeration and temperature are right, mold can grow on almost all foods. The emergence of common tasks or greenish black bread provides a trivial example.

Molds are also able to survive in many other environments seem a priori against inappropriate to life. These are the concentrated solutions of acids, very dilute solutions of certain salts, glue, etc.. However, they can grow in the presence of oxygen.

Molds grow very easily on walls and ceilings of buildings where high humidity is often the form of condensation. They even manage to grow in refrigerators because they tolerate cold better than heat.

Molds are also able to consume acids. Their presence in acidic foods can neutralize the acidity that normally prevents the development of Clostridium botulinum.

Several kinds of molds are found on foods, but the most common are: Aspergillus, Alternaria, Botrytis, Penicillium, Rhizopus and Mucor. They are found mainly in cereals and derivatives, dairy products, meats and cooked meats, oilseeds, fruits and vegetables, dried fruits, jams and beverages (Table 3). Some species are toxigenic, and they produce mycotoxins which ingestion of a sufficient quantity causes poisoning in consumers. However, the presence of a toxigenic species on a foodstuff does not necessarily mean that it is dangerous and it is necessary to investigate and determine the mycotoxins in food in order to confirm or affirm its safety. Indeed, the substrate and environmental conditions play an important role in the production of mycotoxins.

Virus

Viruses can reproduce only within a living cell. They parasitize both multicellular living beings (animals, plants) that unicellular (bacteria, etc.).. They are present in many food products. A distinction is made between specific bacterial viruses (bacteriophages) and infectious virus specific animal cells.

Bacteriophages attack the intestinal flora and cause disturbances more or less serious. They are found on foods that support a large number of bacteria-host. They are spread through fecal-oral route.

The infectious virus specific animal cells are found in certain foodstuffs and transmitted also by the fecal-oral.

Examples of viruses, one can mention the polio virus, the virus of hepatitis, echovirus, adenovirus, etc.