Contamination of Foods

The growing plants carry a common microbiome on their surfaces. They could be contaminated by external sources. Animals too have a normal surface flora, as well as an intestinal one. They also release organisms through excretions and secretions. They can are also contaminated by outside sources. Animals and plants with parasitic diseases, of course, carry the pathogen responsible for the illness. The healthy tissues that are inside both animals and plants nevertheless are found to have a small number of living microorganisms or none at all.

What is Food Contamination?

Food contamination is the term used to describe the existence of hazardous microorganisms and chemicals in food products, which may cause health problems for consumers.


1. Contamination of Foods From Soil

  • The soil is home to the largest variety of microorganisms found in any contamination source. The soil’s environment is very complex and various soil types have their own distinct species of bacteria, fungi, protozoa, and algae.
  • The soil is a reservoir of micro-organisms, and it has supplied many of the strains that are used in the production on the industrial scale of enzymes, antibiotics amino acids, vitamins, and other substances that are used in the food and pharmaceutical industries.
  • Soil microorganisms are involved in the process of recycling nitrogenous and organic compounds, which is crucial if the soil is intended to support the development of plants. However, their ability to break down organic compounds complex is what makes them potent spoilage organisms when they are present in food products.
  • The method of protecting food items from dirt is justified because it reduces the risk of inoculating food with spoilage organisms that could cause harm.
  • It is also a highly competitive environment and one where the physico-chemical parameters can be changed very quickly.
  • As a result soil microorganisms and fungi develop resistant structures like the endospores of Bacillus and Clostridium sclerotia and chlamydospores of numerous fungi, that are able to endure desiccation and a broad variety of temperature fluctuations.
  • Bacterial endospores have a particular resistance to high temperatures. In fact, their subsequent germination can be initiated by exposure to high temperatures. Furthermore, their frequent presence in soil makes them an extremely potent source of loss of food and food-borne poisoning bacteria as well as Clostridia.
  • There are many kinds of microorganisms, but large quantities are also found in soils that are fertile, and capable of contaminating the surface of plants that grow within them or on them, and the surfaces of animals who roam all over the earth.
  • Soil dust is whipped by air currents. Soil particles are transported by flowing water to enter or onto food items.
  • The soil is a major source of heat-resistant spore-forming bacteria.
  • Most important are different yeasts and molds, as well as species belonging to the bacterial genera Bacillus, Clostridium, Enterobacter, Escherichia, Micrococcus, Alcaligenes, Flavobacterium, Chromobacterium, Pseudomonas, Proteus, Streptococcus, Leuconostoc, and Acetobacter, as well as other higher bacteria like the actinomycetes and iron bacteria.
  • Modern methods of handling food generally involve cleaning the food’s surfaces, and, consequently, the removal of most of the soil off these surfaces. Also, care is taken to ensure that food surfaces are not contaminated with soil dust.

2. Contamination of Foods From Water

  • The aquatic ecosystem is in terms of area and volume, the biggest portion of the biosphere. Both sea and freshwater have a variety of micro-organisms that have been adapted to specific habitats.
  • Natural waters are not just home to their own flora, but also microorganisms that come from the soil, and perhaps from animals or wastewater.
  • The surface waters of streams and storage waters in large ponds and lakes differ in levels of microbial matter, ranging from thousands per milliliter following an event of rain to the small numbers that are the result of the self-purification of calm lakes and ponds, or from flowing water.
  • The water that comes from springs and wells has traversed layers of soil and rock to a certain level; therefore, the majority of the bacteria along with the majority of the other suspended materials has been eliminated. The number of bacteria in these water sources could vary from a few hundred to hundreds of microliters of bacteria.
  • The types of bacteria found in natural waters include mainly varieties of Pseudomonas, Chromobacterium, Proteus, Micrococcus, Bacillus, Streptococcus (enterococci), Enterobacter, and Escherichia. The bacteria that live in the waters around fish, as well as other sea creatures, establish themselves on the surface as well as in the digestive tracts that comprise marine fauna.
  • The fish’s surfaces from cold waters in the open ocean will be able to display a bacterial flora that reflects their surroundings and comprises primarily psychrophilic and psychrotrophic species.
  • A lot of these organisms break down macromolecules, like proteins, polysaccharides, and lipids. They could be able to double in as little as ten minutes at temperatures of 0-7°C. So, in 10 days, i.e. the time of 240 hours, a single organism could have grown to 2^24 or between 10^7 and 10^8 in these conditions. If a flora is at the numbers, it may be the cause of off-odors. This could lead to deterioration.
  • Fungi are found in fresh and marine waters, however, they don’t have the same importance in food microbiology like other microorganisms. Certain groups include aquatic fungi, including some micro-organisms as well as Food Materials which are serious pathogens of fish and molluscs. They comprise members of all the major terrestrial fungi: ascomycetes, basidiomycetes, zygomyce and deuteromycetes. There is a possibility that a certain species of this diverse flora may cause the spoilage of the food product that is specialized and related to water like a salad crop that is grown with an overhead irrigation source from the lake or river however this is only speculation.
  • The aquatic photosynthetic micro-organisms such as the cyanobacteria or blue-green algae, which are found among the prokaryotes as well as the dinoflagellates in the eukaryotes, have affected the safety and quality of food. Both of these micro-organisms produce extremely toxic metabolites that can be trapped in shellfish, but without doing any harm. When humans consume them however, they could cause serious disease, such as toxic shellfish paralysis.
  • In general, however, water is more significant in terms of the types of microorganisms it could introduce into food items or onto them as opposed to the total number. Contamination can be caused by the use of water in production.
  • For washing food as well as cooling hot foods and also for manufacturing frozen ice to preserve food items. Each food product is certain microorganisms that need to be avoided in particular.
  • The gas-forming bacteria coliform can enter milk through cooling tank water and cause problems for cheese made from milk.
  • Anaerobic gas forming gas can get into food items through soil-laden water.
  • The cooling water in canneries typically includes coliform as well as other bacteria that spoil food that can enter the canned food during cooling by tiny holes in the seals and seams of the cans.
  • Bacteria that cause ropiness in milk e.g., Alcaligenes viscolactis * and Enterobacter aerogenes, are usually derived from water, and so the slime-making species from Achromobacter and * Alcaligenes and Pseudomonas that cause problems within cottage cheese. The bacterium responsible for the taint that appears on the surface of butter Pseudomonas putrefaciens, comes mostly from water.

Source of Microorganisms in Sea Water

  • The waters around the coasts are affected by the inputs of freshwater and terrestrial micro-organisms as well as, more important, human activities.
  • The sea has evolved into an excellent place to dispose of wastewater and other waste products and, while it’s certain that the oceans have the capacity to disperse these substances and remove them from the environment, however, the extent of human activities has had a negative impact on the coastal waters.
  • If the waters are affected by sewage, there’s always the chance that enteric bacteria from affected people could be present and will be absorbed by food filtering activities of shellfish.
  • Insidious diseases like hepatitis or typhoid fever as well as less severe illnesses such as gastroenteritis are caused by eating oysters and mussels, which appear to be completely regular in appearance and taste.
  • In warmer waters, even water that is not polluted might contain substantial amounts of Vibrio parahaemolyticus. These could also be absorbed by the filter feeding of shellfish. Indeed, they could form a permanent element of the natural in the flora that is found in some shellfish. This organism could be the cause for food poisoning outbreaks particularly in connection with sea food.

Source of Microorganisms in Fresh Water

  • The fresh water of lakes and rivers contain a diverse flora of microorganisms that will include real aquatic species as in components derived from animal, terrestrial and plants.
  • Similar to the ocean waters of the oceans fresh water could be a source for protozoa, bacteria, and viruses that cause illness through contamination of sewage effluents that contain human faecal materials.
  • They do not typically grow in lake and river water , and can be found in extremely small, nevertheless significant numbers, which makes it difficult to prove their presence using specific methods.
  • It is typical to assess the possibility of these bacteria by searching for a specific kind of bacterium that is found in constant amounts in human faeces. will not grow within freshwater, however it can survive for at least the same time as pathogens.
  • The organism is also known as an indicator organism and the most commonly used species for temperate climates is Escherichia Coli.

How to Treat Water

It’s clear from the discussion above that it is crucial to select a place with an adequate water supply before setting up a facility to process or handle food items and food items. It is often required for the treatment of water in order to ensure it is of satisfactory chemical and bacteriological purity. The water supply should be secured from sewage contamination. They can be cleansed through sedimentation in lakes or reservoirs as well as through filtration using filters made of sand or other finer materials or through chlorination, ultraviolet radiation, or boiling. The purification process is only likely to occur as a result of sedimentation. Filtration that is efficient greatly reduces Microbial content, but the filters may cause contamination of water by harmful bacteria. So, filters used for water that is used for drinks has been observed to contain significant amounts of coliform bacteria. Treatment of water using ultraviolet radiation has been utilized on soft drink water.

3. Contamination of Foods From Air

  • Food contamination from the air can be crucial both for health and economic reasons.
  • Disease-causing organisms, in particular respiratory infections, could be spread to employees via air. Or, the food products could be infected.
  • The number of microorganisms that can be found in food items can increase from air, particularly if the air is used to aerate the product, for instance, in the production of bread yeast, however the number of microorganisms brought in by air sedimentation are not significant.
  • Spoilage organisms could be derived from the air, or they may be which interfere with food fermentations.
  • Airborne mold spores can cause issues in meat, cheese and sweetened condensed milk and bacon and bread slices.

Sources of Microorganisms in Air

  • Air doesn’t contain an organic flora of microorganisms All of them have gotten from the air by chance and occur on suspended solids or in water droplets.
  • Microorganisms are able to enter the air through dust or lint, dry soil, spray from lakes, streams or oceans; drops of moisture from coughing speaking, or sneezing; and the growth of sporulating molds on ceilings, walls and floors, as well as food items and other ingredients.
  • So the air around factories that manufacture yeast is awash in yeasts and the air around dairy plants may be contaminated with bacteriophages , or at the very least the starter bacteria that are utilized in the plant.

Types of Microorganisms in Air

  • The airborne microorganisms don’t have the opportunity to grow they simply remain there and the ones that are the most resistant to the effects of desiccation will survive the longest.
  • The spores of mold, due to their small size, their resistance to drying, as well as their large number per mold plant generally are found in the air. Most mold spores don’t easily water-wet and have a lower chance of disperse out of humid environments than particles that are easily wet.
  • There is a possibility for every type of bacterium or fungus to be found in the air, particularly in dust or droplets of water, but certain types are more prevalent than others in uninhibited air. Cocci generally are more prevalent than rod-shaped bacteria, and bacteria spores are not common in air that is free of dust.
  • The chromogenic asporogenous yeasts, particularly the asporogen ones, can be found in the majority of air samples. Naturally, when the dust or sprays made of different materials are released in the air microorganisms associated with those suspended substances will be present, including soil organisms from soil as well as dust as well as water organisms from water sprays plants, and organisms that feed on or fodder dust, etc.

Numbers of Microorganisms in Air

  • The number of microorganisms that are present in the air at any given moment is influenced by such variables as the volume of movement, sun as well as humidity, the place of residence, as well as the quantity of dust that is suspended or spread.
  • The numbers vary in the range of less than one cubic foot on a mountaintop to thousands of people in the extremely dusty air.
  • Individual microorganisms as well as those on suspended dust or droplets settle out in the quiet air. Conversely, moving air draws organisms into it.
  • Thus, the number of microorganisms that live in air are increasing due to airflow caused by movement of people, through air circulation, and also by air breezes.
  • Sun’s direct rays destroy microorganisms that are suspended in the air and, consequently, reduce their numbers.
  • Dry air generally has more microbes than the same air when it is in humid situation.
  • Rain or snow sifts out creatures from air making a steady regular rain could effectively cleanse the air of all living things.
  • Based on a review of the airborne contamination of food products from Heldman (1974) different studies have revealed the following: (1) the Microbial populations of the different processing facilities are comparable, (2) populations vary drastically in the number of people living in the one area of a plant to the next, (3) population in the plant is correlated to air quality outside of the plant as well as (4) the levels of population are linked to the level of work activity of the workers.

Treatment of Air

  • It has been noted that the number of microorganisms present in the air could be reduced under natural conditions due to the sun’s rays, sedimentation, or washing off by snow or rain The removal of microorganisms from air through artificial means could require these methods or the ones of chemical treatment, filtration as well as electrostatic precipitation.
  • The most widely employed of these techniques is through fibers of various sorts, e.g., cotton, fiberglass, or activated carbon.
  • The fibers are changed regularly or sterilized using heat or gas. The washing process using a spray of water or steaming water through a bubbler is not effective and rarely is it used on its own.
  • Air-cleaning chemicals are becoming more popular.
  • The passage of air through tunnels lined by ultraviolet lamps, or the placement of these lamps in space or on a surface where air pollution is believed to be a problem is done in some locations.
  • Electrostatic precipitation of microorganisms and dust particles from the air has also been done with success.
  • Treatment of air using heat at extremely high temperatures has proved to be successful however it is costly.
  • After the microorganisms are eliminated from the air, steps are required to avoid their re-entry.
    • Positive pressure in rooms keep the outside air out.
    • Filters in ventilating or air-conditioning systems prevent the spread of organisms from one part of a plant to another, and ultraviolet-irradiated air locks at doors reduce the numbers of organisms carried in by workers.

4. Contamination of food from From Green Plants And Fruits

  • The natural flora on the surface of plants is different depending on the plant, but generally comprises the species Pseudomonas, Alcaligenes, Flavobacterium as well as Micrococcus along with coliforms and bacteria that produce lactic acid.
  • Lactobacillus plantarum and lactobacillus brevis, Leuconostoc mesenteroides and dextranicum and Streptococcus Faecalis and faecium.
  • The Bacillus species and yeast and molds are also present.
  • The number of bacteria depends on the plant’s condition and the environment which can range from a few hundred to thousands per square centimeter surface area to millions.
  • The exterior of a properly cleaned tomato, for instance, could have 400-700 microorganisms for every square centimeter, even an unwashed tomato could have a number of thousand.
  • The outer layer of cabbage that is not washed may contain anywhere from 1 up to two million microorganisms in a grams, however cut and washed cabbage may contain between 200,000 and 500,000.
  • The tissue inside the cabbage, which is where the leaves’ surface will be home to the majority of the natural flora, has less varieties and less numbers, which range between a few hundred and 150,000 grams.

Source of Microorganisms

  • The surfaces of plants that are exposed are contaminated by soil, air, water, sewage and even animals, meaning that microorganisms that come from these sources are added to natural plant flora.
  • If the conditions for the expansion of natural flora as well as contamination are present, an increase in the numbers of certain types of microorganisms occur particularly after harvesting, which we will discuss later.
  • Certain fruits have been discovered to have viable microorganisms within their insides.
  • Healthy, normal tomatoes have been found to be contaminated with coliforms, Pseudomonas, Achromobacter * , Micrococcus and Corynebacterium and yeasts were found in healthy, unharmed tomatoes. Organisms have also been discovered in the health tuber and root vegetables.

5. Contamination Of Foods From Animals

  • Animal sources of microorganisms include the flora of the surface and the flora of the respiratory tract as well as the flora of the digestive tract.
  • The natural surface flora found in meat animals typically isn’t so important as the microorganisms that pollute their respiratory tracts or intestinal tracts.
  • However hides, hooves and hair are not just home to huge quantities of microorganisms that come from manure, soil water, and feed but as well important types of spoilage organisms.
  • The feet and feathers of chickens carry heavy contaminants from the same sources.
  • The skin of a lot of meat animals could include staphylococci, micrococci as well as beta-hemolytic streptococci.
  • Staphylococci in the skin, or in the respiratory tract can get onto the carcass before moving on onto the final product.
  • The feces and products contaminated by feces of animals may contain a variety of species of enteric bacteria, such as Salmonella.
  • In animals, Salmonellosis may result in the contamination of from animal products or by-products and, consequently, contaminate food products that are derived from them Salmonella.
  • The carcasses of pigs or cattle could be infected with salmonella.
  • In the course of further processing and handling, the majority of these organisms do not produce human salmonellosis.
  • Actually, the meat that comes from slaughtered animals is rarely connected with salmonellosis in humans.
  • The risk of salmonellosis in eggs has been decreased as a result the pasteurization process used in eggs and egg products.
  • A variety of infectious diseases that originate from animals are transmitted to humans through food items, but this is just one of many transmission routes.
  • A lot of these illnesses are being eliminated or lessened through improved management of animals, but the list of agents of animal diseases that can cause infection from foods could be Brucella, Mycobacterium, tuberculosis, Coxiella, Listeria, Campylobacter beta-hemolytic streptococci Salmonella Enteropathogenic Escherichia Coli as well as parasites and viruses.
  • From the most primitive to the most advanced forms are responsible for their waste and then their bodies to the soil and water, and to the plants that are growing there.
  • Little attention has been paid to the contamination direct of plants that feed us resulting from this source, except as enterococci or coliform bacteria could be present. Birds and insects cause mechanical harm to vegetables and fruits, introducing microorganisms, and opening the door to microbial spoilage.

6. Contamination Of Foods From Sewage

  • If untreated domestic sewage is used to fertilize plants it is likely that plant foods that are consumed raw could be contaminated by bacteria that are harmful to humans, specifically those that cause digestive diseases.
  • The usage of “night soil” as a fertilizer continues to be used in certain regions of the world, however, it is not common across the United States.
  • In addition to pathogens, coliform bacteria enterococci, anaerobes, intestinal bacteria, and viruses could contaminate food items through this source.
  • Natural waters that are contaminated by sewage can contribute to microorganisms that cause fish, shellfish and other fish.
  • The treated sewage that is pumped into the soil or into the water provides microorganisms. However, it is likely to contain fewer and fewer pathogens than raw water or sewage.

7. Food Contamination During Handling And Processing

  • The contamination of food products by the natural sources discussed could happen prior to the time that food items are collected or harvested, or even during the processing and handling or processing.
  • The additional contamination can come from equipment that is in contact with food or packaging materials as well as from the personnel.
  • The processor tries to wash as well as “sanitize” equipment to reduce the risk of contamination. It also employs packaging materials that reduce contamination.
  • The word “sanitize” is used here in place of “sterilize” because although an attempt to sterilize device, i.e., free it from all life-forms and organisms that can live in it, the goal of sterility has not been achieved.
  • Workers in food processing facilities are at risk of contaminating food when processing and handling.
  • Many researchers suggest human beings shed anywhere from 103 to 104 viable living organisms every minute.
  • The number and type of living organisms that are shed is connected to the subject’s work conditions.
  • The role of food handlers in outbreaks of foodborne diseases is well-established from a public health perspective the source for contamination attracted significant focus.

8. Other Sources of Contamination

  • Animal hides: In the case of cows that milk the kinds of bacteria present in milk raw can reflect the biota in the udder if proper protocols are not adhered to during the process of milking, as well as in the general environment that surrounds these animals. In both the udder as well as the hide, bacteria can be a threat to the general surroundings, the milk containers as well as the handles of handlers.
  • Animal Feeds: The food source is the cause of salmonellae in livestock and poultry. If you’re using silage, it’s an established food source for Listeria monocytogenes that affect meat and dairy animals. The organisms that are found in dry animal feed are dispersed all over the animal population and could appear on hides of animals.
  • Gastrointestinal Tract Biota: This organ becomes a source of water in the event that polluted water can be used for washing foods. The intestinal biota comprises several organisms that do not remain as long in water like other organisms of them, and among them are pathogens like salmonellae. All or any of Enterobacteriaceae could be present in fecal wastes together with intestinal pathogens, including the protozoal species of five that are already mentioned.
  • Food Utensils: If vegetables are harvested in containers as well as Utensils, it is normal to find at least some of the organisms living on the surfaces of the product to infect the surfaces they contact. When increasing amounts of vegetables are stored inside the container there will be a normalization of microbiota could take place. In the same way cutting blocks in a market for meat as well as cutting grinders and knives are affected by the initial samples This creates a plethora of microorganisms, ensuring the constant contamination of meat-borne bacteria.


  • Hussain MA. Food Contamination: Major Challenges of the Future. Foods. 2016 Mar 23;5(2):21. doi: 10.3390/foods5020021. PMID: 28231116; PMCID: PMC5302336.

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