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Food BiotechnologyDr. Kamal E. M. Elkahlout

Food Microbiology 2 Sources of

microorganisms in food& Important Bacterial

Groups in Foods

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Sources of microorganisms in foods

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• The internal tissues of healthy plants (fruits and vegetables) and animals (meat) are essentially sterile.

• Raw and processed (except sterile) foods contain different types of molds, yeasts, bacteria and viruses.

• Microorganisms get into food from natural sources and external sources.

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Natural sources for foods of plant origin

• Surfaces of fruits, vegetables and grains and damaged tissues and pores in some tubers (e.g. radish and tubers).

Natural sources for foods of animal origin

• Skin, hair, feathers, gastrointestinal tracts, urinogenital tract, respiratory tracts and milk ducts (teat canals) in animals producing animals.

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An understanding of the sources of microorganisms in food is important to:

• develop methods to control access of some microbes in food.

• develop processing methods to kill them in food.

• Determine the microbiological quality of foods.

• Setup microbiological standards and specifications of food and food ingredients.

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Pre dominant microorganisms in plants (fruits and vegetables).

• Internal tissues are sterile except for few porous vegetables and leafy vegetables.

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

• Fruits and vegetables harbour microbes on their surfaces and microbe presence depends on their type, soil condition, water used and air quality.

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• Molds and yeasts

• Lactic acid bacteria

• Bacteria from the genera: Pseudomonas, Alcaligenes, Micrococcus, Erwina, Bacillus, Clostridium and Enterobactor.

• Pathogens especially of enteric types (Salmonella, Escherichia coli, Campylobacter, Shigella, Cyclospora, Giardia can be present if the soil is contaminated with untreated sewage.

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Factors contributing to increase in microbial numbers

• Diseases of the plants.

• Damage of the surface before (during and after harvest).

• Long delays between harvesting and washing. • Unfavorable storage and transport conditions after

harvesting and before processing can greatly increase the microbial numbers.

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Reducing microbial loads in foods of plant origin

• Proper methods used during growing (such as use of treated sewage or other types of fertilizers).

• Damage reduction during harvesting.

• Quick washing with good quality water to remove soil and dirt.

• Storage at low temperature before and after processing.

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• Are carriers and can carry pathogens such as – Salmonella spp., pathogenic Escherichia coli,– Campylobacter jejuni, Yersinia enterocolitica

and Listeria monocytogenes

• Laying birds – suspect of carrying Salmonella enteritidis in ovaries and contaminating yolk during ovulation.

• Fish and shellfish carry normal microflora in the scales, skin and digestive tracts. Carry pathogens such as Vibrio parahaemolyticus, Vib vulnifus.

Pre dorminant microroganisms in animals birds, fish and shellfish

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Contamination of foods of animal origin during production and processing:

• Milk – contaminated with fecal materials on the udder surface

• Egg shells – contaminated with fecal material

• Meat- contaminated with the intestinal contents during slaughtering

• Enteric pathogens from fecal materials common are Staphylococcus aureus, Micrococcus spp, moulds and yeasts.

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Reduction in microbial load – foods of animal origin• Effective use of husbandry of live animals and birds:

- good housing- avoid overcrowding- supply of uncontaminated water

• Testing animals and birds for pathogens and culling the carriers-to reduce the incidence of pathogenic microorganisms in food.

• Cleansing carcasses with good quality water.

• Careful hair, feather removal and digestive, urinogenital and respiratory organs.

• Proper sanitation during slaughtering and processing.• Proper cleaning of the udder before milking and after milking.• Eggs should be collected soon after laying and washed and stored as per

recommended procedures.

• Fish and marine products should be harvested from unpolluted waters. Observe proper sanitation during processing. Use ice for storage.

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Sources of microorganismsAir

• Microorganisms are present in dust in air

• Do not grow in dust but are transient and variable depending upon the environment

• Their level is controlled by the degree of – humidity, size and level of dust particles, – temperature and air velocity and resistance of

microorganisms to drying

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• Dry air with low dust content and higher temperature has a low microbial level.

• Predorminant microbes in air include spores of Bacillus spp. Clostridium spp., mold and Gram-positive bacteria (Micrococcus spp and Sarcina).

• Microbial contamination in the air can be reduced by – removing the potential sources,

– controlling dust particles in the air (using filtered air) using positive air pressure,

– reducing the humidity level and installing UV light.

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Soil• Soil contains several varieties of microorganisms

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

• Moulds, yeasts and bacteria genera (Enterobacter, Pseudomonas, Proteus, Micrococcus, Enterococcus, Bacillus and Clostridium) can get into foods from the soil.

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• Soil contaminated with fecal materials can be source of enteric pathogenic bacteria

• Sediments where fish and marine foods are harvested can also be a source of microorganisms in those foods

• Prevention - removal of soil (and sediments) and avoiding soil contamination are used to reduce microorganisms in foods

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Sewage

• Sewage when used as fertilizer in crops can contaminate food with microorganisms.

• Predominant types include enteropathogenic bacteria and viruses.

• Major concern with organically grown foods and many imported fruits and vegetables where untreated sewage may be used as fertilizers.

• Prevention –

– not to use sewage as fertilizers, or should be efficiently treated to kill the pathogens.

– Wash foods following harvesting is important

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Water

• Is used to produce, process and in some cases store foods.

• Used for irrigation of crops, drinking by food animals.

• Raising fishery and marine products.

• washing foods, processing (pasteurization canning and cooling of heated foods).

• washing and sanitation of equipment , processing and transportation facilities

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• Water is used as an ingredient in many processed foods thus can greatly influence the microbial quality of foods.

• Wastewater can be recycled for irrigation

• Chlorine-treated potable water should be used in processing, washing, sanitation and as an ingredient.

• Although potable water does not contain coliforms and pathogens. It can contain other bacteria capable of causing food spoilage (including Pseudomonas, Alcaligenes and Flavobacterium)

• Improperly treated water can contain pathogen and spoilage microorganisms

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Humans

• Between production and consumption foods come in contact with people handling the foods.

• people working in a food processing plant, handling foods at restaurants, catering services, retail stores and at home.

• Improperly cleaned hand, lack of aesthetic sense and personal hygiene, dirty clothes and hair can be a major sources of microbial contamination in foods.

• Pathogens such as Staphylococcus aureus, Salmonella spp. Shigella spp. Pathogenic E. Coli and hepatitis A can be human sources.

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Food ingredients

• prepared or fabricated foods many ingredients or additives are included in different quantities.

• Many ingredients can be a source of both spoilage and pathogenic microorganisms

• various spices can possess very high populations of mold and bacterial spores.

• Starch, sugar and flour might have spores of thermophilic bacteria.

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• ingredients should be produced under sanitary conditions.

• and given antimicrobial treatments.

• Setting up acceptable microbial specifications for the ingredients will be important in reducing microorganisms in foods from this source

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Equipments • wide variety of equipment are used in

– harvesting, transportation, – processing and storage of foods

• microorganisms from air, raw foods, water and personnel can get into the equipment and contaminate foods.

• Depending on environment and time, – microbes can multiply from low initial population to

reach high level and contaminate large volumes of foods

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• processing used continuously for a long period of time, – microorganisms resent initially can multiply and

act as a continuous source of contamination in the product.

• small parts, inaccessible sections and certain materials may not be efficiently cleaned and sanitized therefore can serve as sources of both pathogenic and spoilage microorganisms in food

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• Small equipments such as cutting boards, knives, spoons due to improper cleaning can be source of cross-contamination

• Salmonella, Listeria, Escherichia, Enterococcus, Micrococcus, Pseudomonas, Lactobacillus, Listeria and yeasts and moulds can get into food from equipment

• Proper cleaning and sanitation of equipment at prescribed intervals are important

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Miscellaneous sources

Several other sources of food contamination include :

• Many types of packaging materials are used in food. (wrapping materials, containers).

• Flies, birds, house pets and rodents.

• proper microbiological standards (or specifications) for packaging materials are necessary

Important Bacterial Groups in Foods

Lactic Acid bacteria• produce relatively large quantities of lactic acid

from CHO's. • Lactoccus, Leuconostoc, Pediococcus,

Lactobacillus and Streptococcus thermopillus

Lactococcus Leuconostoc

Lactic Acid bacteria

Pediococcus

Lactobacillus

Streptococcus thermopilus

Acetic acid bacteria• bacteria that produce acetic acid.

• Acetobacter aceti.

Propionic acid bacteria• bacteria that produce propionic acid and are

used in dairy fermentation. • Propionibacterium freudenreichii.

Butyric acid bacteria• bacteria that produce butyric acid in relatively

large amounts. • Some Clostridium spp such as Clostridium

butyricum .

Proteolytic bacteria• those that are capable of hydrolyzing

proteins, due to production of extracellular proteinases.

– Species in genera Micrococcus, Staphylococcus, Bacillus, Clostridium, Pseudomonas, Alteromonas, and Flavobacterium.

Proteolytic bacteria

StaphylococcusMicrococcus

Bacillus

Pseudomonas

Clostridium Flavobacterium

Lipolytic bacteria• able to hydrolyze triglycerides due to

production of extracellular lipases. – Species in genera Micrococcus,

Staphylococcus, Pseudomonas, Alteromonas and Flavobacterium.

Alteromonas

Saccharolytic bacteria• able to hydrolyze complex CHO's.

• Bacillus, Clostridium, Aeromonas, Pseudomonas and Enterobacter.

AeromonasEnterobacter

Thermophilic bacteria• able to grow at 50°C and above.

• Include some species from genera Bacillus, Clostridium, Pediococcus, Streptococcus and Lactobacillus.

Pediococcus

Psychrotrophic bacteria able to grow at refrigerated temperatures

(5°C). Pseudomonas, Alteromonas, Alcaligenes,

Flavobacterium, Serratia, Bacillus, Clostridium, Lactobacillus, Leuconostoc, Carnobacterium, Brochothrix, Listeria, Yersinia and Aeromonas.

Alcaligenes Serratia

Listeria

Thermoduric bacteria• able to survive pasteurization temperature

treatment. • Include some species from Micrococcus,

Enterococcus, Lactobacillus, Pediococcus, Bacillus (spores) and Clostridium (spores).

Enterococcus

Halotolerant Bacteria able to survive high salt concentrations (10%).

Bacillus, Micrococcus, Staphyloccus, Pediococcus, Vibrio and Corynebacterium.

Vibrio

• Aciduric Bacteria: – able to survive at low pH (below 4.0).

• Lactobacillus, Pediococcus, Lactococcus, Enterococcus and Streptococcus.

• Osmophilic bacteria:– can grow in a relatively higher osmotic environment

than other bacteria. • Some species from genera Staphylococcus,

Leuconostoc and Lactobacillus are included. They are much less osmophilic than yeasts and molds

Gas-producing bacteria produce gas (CO2, H2, H2S) during metabolism of nutrients.

Leuconostoc, Lactobacillus, Propionibacterium, Escherichia, Enterobacter, Clostridium and Desulfotomaculum.

Escherichia

• Slime Producers:

– produce slime due to synthesis of polysaccharides.

• Xanthomonas, Leuconostoc, Alcaligenes, Enterobacter, Lactococcus and Lactobacillus.

• Sporeformers:

– ability to produce spores. • Bacillus, Clostridium and Desulfotoaculum

spp.

They are divided into • aerobic sporeformers, • anaerobic sporeformers, • flat sour sporeformers, • thermophilic sporeformers • sulfide-producing sporeformers.

• Coliforms:

– includes species of Escherichia, Enterobacter, Citrobacter and Klebsiella and used as index of sanitation.

• Fecal Coliforms: – mainly Escherichia coli. Also used as index

of sanitation.

• Enteric Pathogens:

– includes pathogenic Salmonella, Shigella, Campylobacter, Yersinia, Escherichia, Vibrio, Listeria,

– hepatitis A and others that can cause gastrointestinal infection.