1 Food Biotechnology Dr. Kamal E. M. Elkahlout Food
Microbiology 2 Sources of microorganisms in food & Important
Bacterial Groups in Foods
Slide 2
2 Sources of microorganisms in foods
Slide 3
3 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.
Slide 4
4 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.
Slide 5
5 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.
Slide 6
6 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.
Slide 7
7 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.
Slide 8
8 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.
Slide 9
9 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.
Slide 10
10 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
Slide 11
11 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.
Slide 12
12 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.
Slide 13
13 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
Slide 14
14 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.
Slide 15
15 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.
Slide 16
16 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
Slide 17
17 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
Slide 18
18 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
Slide 19
19 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
Slide 20
20 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.
Slide 21
21 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.
Slide 22
22 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
Slide 23
23 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
Slide 24
24 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
Slide 25
25 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
Slide 26
26 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
Slide 27
Important Bacterial Groups in Foods
Slide 28
Lactic Acid bacteria produce relatively large quantities of
lactic acid from CHO's. Lactoccus, Leuconostoc, Pediococcus,
Lactobacillus and Streptococcus thermopillus Lactococcus
Leuconostoc
Acetic acid bacteria bacteria that produce acetic acid.
Acetobacter aceti.
Slide 31
Propionic acid bacteria bacteria that produce propionic acid
and are used in dairy fermentation. Propionibacterium
freudenreichii.
Slide 32
Butyric acid bacteria bacteria that produce butyric acid in
relatively large amounts. Some Clostridium spp such as Clostridium
butyricum.
Slide 33
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.
Lipolytic bacteria able to hydrolyze triglycerides due to
production of extracellular lipases. Species in genera Micrococcus,
Staphylococcus, Pseudomonas, Alteromonas and Flavobacterium.
Alteromonas
Slide 36
Saccharolytic bacteria able to hydrolyze complex CHO's.
Bacillus, Clostridium, Aeromonas, Pseudomonas and Enterobacter.
Aeromonas Enterobacter
Slide 37
Thermophilic bacteria able to grow at 50C and above. Include
some species from genera Bacillus, Clostridium, Pediococcus,
Streptococcus and Lactobacillus. Pediococcus
Slide 38
Psychrotrophic bacteria able to grow at refrigerated
temperatures ( 5C). Pseudomonas, Alteromonas, Alcaligenes,
Flavobacterium, Serratia, Bacillus, Clostridium, Lactobacillus,
Leuconostoc, Carnobacterium, Brochothrix, Listeria, Yersinia and
Aeromonas. Alcaligenes Serratia Listeria
Slide 39
Thermoduric bacteria able to survive pasteurization temperature
treatment. Include some species from Micrococcus, Enterococcus,
Lactobacillus, Pediococcus, Bacillus (spores) and Clostridium
(spores). Enterococcus
Slide 40
Halotolerant Bacteria able to survive high salt concentrations
( 10%). Bacillus, Micrococcus, Staphyloccus, Pediococcus, Vibrio
and Corynebacterium. Vibrio
Slide 41
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
Slide 42
Gas-producing bacteria produce gas (CO 2, H 2, H 2 S) during
metabolism of nutrients. Leuconostoc, Lactobacillus,
Propionibacterium, Escherichia, Enterobacter, Clostridium and
Desulfotomaculum. Escherichia
Slide 43
Slime Producers: produce slime due to synthesis of
polysaccharides. Xanthomonas, Leuconostoc, Alcaligenes,
Enterobacter, Lactococcus and Lactobacillus.
Slide 44
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.
Slide 45
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.
Slide 46
Enteric Pathogens: includes pathogenic Salmonella, Shigella,
Campylobacter, Yersinia, Escherichia, Vibrio, Listeria, hepatitis A
and others that can cause gastrointestinal infection.