Download Sources of microorganisms in food.

Food Biotechnology
Dr. Kamal E. M. Elkahlout
Food Microbiology 2
Sources of
microorganisms in food
& Important Bacterial
Groups in Foods
1
Sources of microorganisms in foods
2
• 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.
3
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
4
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.
5
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.
6
• 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.
7
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.
8
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.
9
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.
10
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.
11
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.
12
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
13
• 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 Grampositive 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.
14
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.
15
• 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
16
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
17
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
18
• 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
19
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.
20
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.
21
• 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
22
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
23
• 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
24
• 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
25
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
26
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
Streptococcus thermopilus
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
Micrococcus
Bacillus
Staphylococcus
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.
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).

Alcaligenes
Pseudomonas, Alteromonas, Alcaligenes,
Flavobacterium, Serratia, Bacillus, Clostridium,
Lactobacillus, Leuconostoc, Carnobacterium,
Brochothrix, Listeria, Yersinia and Aeromonas.
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.