Transcript Sources of Foodborne Enteric Microbial Contamination

ENVR 191
Food Safety and Foodborne Disease
Lecture 2 - December 6, 1999
Mark D. Sobsey
Hazard Analysis/Critical Control Points (HACCP)
A program of process control to (1) identify microbial
hazards, (2) identify the most vulnerable (critical) sites
or steps in the process and (3) implement an in-house
monitoring system for quality assurance and hygiene.
Incorporates elements of:
(i) education and training,
(ii) ingredient or commodity control,
(iii) process control,
(iv) inspection, and
(iv) microbiological and related surveys
Design and implement on a commodity-specific and production
facility-specific basis
Methods to Control Fecal Contamination of Foods
• Prevention: keep enteric microbes out
• Remove enteric microbes:
– identify and remove contaminated food items and ingredients
– wash to remove contaminants filtration or other physical
separation methods
– depurate or relay live shellfish.
• Use of heat
– sterilize
– disinfect (e.g., pasteurize and cook to destroy pathogens
• Use of cold and freezing
– cold storage and freezing to prevent proliferation
• Drying, dehydration and intermediate-moisture processing
• Chemical treatments: disinfect and sanitize
• Irradiation: UV and gamma (ionizing) radiation
Heat and Thermal Treatment
• Effects of heat vary with:
– food composition: water, fat, proteins, carbohydrates, salts and pH
– organism factors: form, composition, growth stage, age, etc.
• Sterilize (or nearly sterilize) foods (destroys all viable microbes)
– Heat >100oC; usually uses high pressure and steam;
– Typical target temperature is 115-116oC for about 60 minutes.
• Example: Retorting of Canned Foods.
• Pasteurization:
– Intended to kill pathogens;
– Does not sterilize the food;
– Often used prior to subsequent cold storage so pathogens or
spoilage organisms do not proliferate.
• High Temperature-Short Time Method: 72oC; 15 sec. (milk)
• Low Temperature-Long Time Method: 62.8oC for 30 min.(milk)
– Pasteurization times and temperatures for other foods depend on the
effects of heat on the food, food composition and the target
organisms of interest.
Thermal Destruction of Microbes:
Thermal Death Time and D Value
– Assumes first-order
(exponential; log-linear)
destruction kinetics
100-----
Survivors (%)
• Thermal Death Time (TDT):
time needed to kill a specified
number of organisms at a
specified temperature.
• D value: time needed to
destroy 90% or 1 log10 of
organisms at a specified
temperature
10------------------1--
D value
Time (min.)
Drying, Dehydration and Desiccation
• Low moisture foods: usually <15% moisture
• Intermediate moisture foods (IMF): 15-50% moisture
– fruits, cakes, syrups, candies, jams, milks, some meats and cheeses
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Sun (natural) drying: often used for fruits
Heat drying (dehydration; desiccation)
Freeze drying (lyophilization; cryophilization)
Condensing or evaporating: reducing moisture in a liquid
food; e.g., evaporated or sweetened condensed milk.
• Drying destroys some enteric microbes but is not very
effective for others.
– Inhibitors are often used for dried and IMF foods:
• ex.: potassium sorbate and calcium propionate as fungistats
Chemical Treatments
• Preservatives:
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Most are ineffective against viruses and protozoan cysts
most are designed to control certain bacteria and molds.
propionates, sorbates, benzoates and p-hydroxybenzoates: molds
Nitrates and nitrites (ex., for Clostridia.)
Sulfur dioxide and sulfites
Acetic, lactic and other organic acids
NaCl and sugars
Ethylene and propylene oxides
• Disinfectants and sanitizers:
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Used to treat (by washing or dipping) certain meats and produce
Chlorine, peroxyacetic acid, ozone, hydrogen peroxide
10s to 100s of mg/l; contact times of seconds to minutes
Organic acids (acetic, lactic and citric) at 2-7%; less effective
Food Irradiation
• Ionizing Radiation (X-rays and gamma rays)
– Becoming more widely used.
• Gamma radiation from Co-60 and Cs-137 sources)
– Effectiveness depends on: organism, composition of the food,
temperature, and presence of oxygen
• Undesirable changes in foods from excessive radiation: radiolysis of
water and other chemical reactions on amino acids, etc..
– Doses(approximate) to inactivate 1 log10 of organisms:
• vegetative bacteria: 100-200 Krad
• viruses: 500 Krad
• Cysts and Spores: 500 Krad
• UV Radiation:
– Low (monochromatic 254 nm) mad medium (polychromatic)
– Used primarily for beverages: water, juices, ciders, etc.
Shellfish Depuration and Relaying
• Place live bivalve mollusks shellfish in clean flowing seawater
– Normal pumping, feeding and related activity rids accumulated
microbes
• Relaying:
– transfer shellfish from contaminated (restricted) waters to
uncontaminated natural estuarine waters.
– Typical holding times in the clean water are two weeks or longer.
• Depuration:
– Place restricted shellfish in shore-based tanks of clean, flowing
seawater under controlled conditions for periods of several days
– Factors influencing deputation efficiency:
• tank geometry and loading (quantity of shellfish per volume of tank),
• water quality
• temperature
Factors Influencing Uptake and Persistence of Enteric
Microbes in Shellfish
• Type of microbe: viruses are more persistent than bacteria
• Type of shellfish: differences among shellfish species and genera
• Temperature: uptake and persistence greater at higher temperature (to
a limit); at very low and very high temperature, the animals become
inactive and do not pump water
• Salinity: uptake and persistence greater at higher salinity.
– If salinity is low they become inactive and not pump water.
• Turbidity: excess causes gill clogging and interferes with activity.
– Higher turbidity increases microbial uptake but does not greatly influence
elimination (except for some enteric bacteria).
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Dissolved oxygen: animals become inactive (suffocate at low DO).
pH: in he physiological has little influence on uptake or elimination)
Other water quality factors: toxic chemicals can interfere with activity
Food supply: little direct effect if it does not change pumping activity
Spawning reduces microbial elimination from shellfish.