Sources Of Microorganisms In Foods

Prof. Mohammad Shubair

Microorganisms get into food from both natural sources and from external sources to which a food comes into contact from the time of production until the time of consumption.

Natural sources for foods of animal origin include skin, hairs, feathers, gastrointestinal tract, urogenital tract, respiratory tract, milk ducts(teat canal) in udders of milk animals.

Natural micro-flora exist in ecological balance with their hosts, and their types and levels vary greatly with the types of plants and animals as well as their geographical locations and environmental conditions.

Besides natural microorganisms, foods can be contaminated with different types of microorganisms coming from outside sources such as: air- soil- sewage- water- feeds- human- food ingredients- equipment- packages- insects

Microbial types and their levels from these sources getting into foods vary widely and depend on the degree of sanitation used during the handling of foods.

Predominant Microorganisms In Different Sources

Plants( Fruits and Vegetables)• The inside tissue of foods from plant sources are

essentially sterile except for few porous vegetables( radishes, onion, cabbage).

• Some plants produce natural antimicrobial metabolites that can limit the presence of microorganisms.

• Fruits and vegetables harbor microorganisms on the surface ; their types and level vary with:

soil condition, type of fertilizer, water used, air quality.

Examples of Microorganisms In Plants

Molds, Yeasts, lactic acid bacteria,Pseudomonas, Alcaligenes, Micrococcus, Erwinia, Bacillus, Clostridium, Enterobacter.

Pathogens like enteric types can be present if the soil is contaminated with untreated sewage.

Factors increasing the number of microorganisms in plants:

- Diseases of the plant, damage of the surface, long delay between harvesting and washing, unfavorable storage and transport before processing and improper storage after processing

Reduction of Microbial Load In Foods Of Plant Origin

• Use of treated sewage for fertilizers• Damage reduction during harvesting• Quick washing with good quality water to

remove soil and dirt.• Storage at low temperature before and

after processing.

Animals, Birds, Fish and Shellfish

• Food animals and birds normally carry many types of indigenous microorganisms in gastrointestinal tract, respiratory tract, urogenital tract and teat canal in the udder as well as in skin, hooves, hair and feathers.

• The number of these microorganisms depends on the specific organ e.g. in large intestine >1010/g.

• Many animals act as carriers, they can harbor pathogens like S. aureus, E. coli, Campylobacter, and Listeria without showing symptoms.

• Laying birds may carry S. enteritidis in the ovaries.

• Fish and shellfish carry normal flora in the scales, skin and digestive tracts. They can also carry pathogenic bacteria e.g. V. parahaemolyticus .

• Many spoilage and pathogenic microorganisms can get into foods of animal origin (milk, egg, meat, fishery products) during production and processing.

• Milk can be contaminated with fecal materials on the udder surface.

• Meat can be contaminated with intestinal contents during slaughtering.

• Meat from food animals and birds can be contaminated with several spoilage and pathogenic microorganisms from skin, hair and feathers e.g. S. aureus, Micrococcus, Propionibacterium, Corynebacterium, Molds and Yeasts.

Prevention Of Food Contamination From Animal

SourcesGood housing and supply of uncontaminated

feed and water.Testing animals and birds for pathogens and

culling the carriers.Using good quality water for washing the

carcases.Hair removal.Removal of Contaminated partsProper cleaning of the udder before milking

Cooling milk immediately after milking and processing .

Collection of eggs quickely after laying.Fish and marine products should be harvested

from unpolluted water, and stored properly.

AIR

Microorganisms are present in dust and moisture droplets in the air.

Microorganisms do not grow in dust.Microorganisms in air are transient and variable

depending on the environment.Level of Microorganisms in air is controlled by:• The degree of humidity, Size, Level of dust particles,

Temperature, Air velocity and Resistance to drying .• Dry air with low dust content and higher temperature has

a low microbial level.

Examples Of Microorganisms Present In Air

• Spores of Bacillus Spp.• Clostridium Spp.• Molds and Yeasts• Cells of Gram Positive Bacteria e.g. Micrococcus and Sarcina If the surroundings contain a source of pathogens e.g.

animal and poultry farms or a sewage treatment plant, different types of bacteria including pathogens and viruses can be transmitted via air.

Control Measures: • Removing potential sources, Air filtration, Reducing

humidity, Installing ultra violet lamps.

Soil

• Soil used to grow agricultural produce and raise animals and birds contains several varieties of microorganisms.

• Microorganisms can multiply in soil and their numbers can be very high(billions/g).

Microorganisms Found In Soil:• Molds and Yeasts, Enterococcus, Bacillus, Clostridium,

Enterobacter, pseudomonas, Proteus, Micrococcus and Parasites.

• Soil contaminated with fecal materials can be the in foods. source of enteric pathogens and viruses

Sewage

Sewage can contaminate crops with microorganisms when it is used as fertilizer e.g. enteropathogenic bacteria, viruses and parasites.

Sewage should be treated before using as fertilizer to kill pathogens.

Effective washing of foods following harvesting is important.

Water

• Contamination of foods with pathogenic bacteria , viruses and parasites has been recorded.

• Waste water can be recycled for irrigation. • Potable water may contain bacteria capable of

causing food spoilage such as Pseudomonas, Alcaligenes, flavobacterium.

• Improperly treated water can contain pathogenic and spoilage microorganisms.

• Water used in food processing should be of higher microbial quality than that of potable water.

Humans

Between production and consumption, foods come in contact with different people handling the foods, they include:

• People working in farms• People working in processing plants.• People handling food in restaurants• People in retail stores and at home.• Human carriers have been a source of

pathogenic microorganisms in food.

Major Sources Of Microbial Contamination Of Foods By

Humans• Improperly cleaned hands.• Lack of aesthetic sense and personal

hygiene.• Dirty clothes and hair.• Presence of minor cuts and infection in

hands and face.• Diseases(Influenza, Throat infection,

Hepatitis A and others).

• Pathogens such as S. aureus, Salmonella, Shigella, Pathogenic E. coli, Hepatitis A can be introduced into food from human sources.

Control Measures:• Proper training of personnel in personal

hygiene.• Regular checking of health• Maintaining efficient sanitary and aesthetic

standards.

Food Ingredients

Many ingredients can be the source of spoilage and pathogenic microorganisms

• e.g. Spices have very high populations of mold and bacterial spores

The ingredients should be produced under sanitary conditions.

Setting up acceptable microbial specifications for the ingredients.

Equipment

Equipment can be a source of contamination• Many microorganisms can get in food from

equipment e.g Salmonella, Listeria, Enteric bacteria, Micrococcus, Escherichia, Pseudomonas, Lactobacillus, Leuconostoc, Clostridia, Bacillus, Yeast and Molds.

• Proper cleaning and sanitation of equipment should be emphasized.

Miscellaneous

• Food might be contaminated from other sources; • Packaging and Wrapping materials• Containers• Flies• Vermins• Birds • House pets• Rodents• Proper care should be taken not to contaminate food

from these sources.