Food Biotechnology Dr. Kamal E. M. Elkahlout Food Microbiology 2 Sources of microorganisms in food & Important Bacterial Groups in Foods

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Food Biotechnology Dr. Kamal E. M. Elkahlout Food Microbiology 2 Sources of microorganisms in food & Important Bacterial Groups in Foods. Sources of microorganisms in foods. The internal tissues of healthy plants (fruits and vegetables) and animals (meat) are essentially sterile.
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  • Food BiotechnologyDr. Kamal E. M. ElkahloutFood Microbiology 2 Sources of microorganisms in food
  • & Important Bacterial Groups in Foods
  • Sources of microorganisms in foods
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Pre dorminant microroganisms in animals birds, fish and shellfish
  • 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.
  • 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.
  • 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.
  • Sources of microorganisms Air
  • 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
  • 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.
  • 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.
  • 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
  • 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
  • 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
  • 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
  • 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.
  • 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.
  • 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
  • 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
  • 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
  • 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
  • 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
  • Leuconostoc Lactococcus Lactic Acid bacteria Streptococcus thermopilus Pediococcus Lactobacillus 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 Staphylococcus Micrococcus Pseudomonas Bacillus 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.
  • Aeromonas Enterobacter 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.
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