1. Food Safety and Foodborne Disease
ENVR 191
Food Safety and Foodborne Disease
Lecture 2 - December 6, 1999
Mark D. Sobsey

2. 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

3. 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

4. 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.

5. Thermal Destruction of Microbes: Thermal Death Time and D Value
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
Assumes first-order (exponential; log-linear) destruction kinetics
Survivors (%)
1--
D value
Time (min.)

6. 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
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

7. Chemical Treatments Preservatives: Disinfectants and sanitizers:
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:
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

8. 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.

9. 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

10. 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).
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.