Food Microbiology II Flashcards
Water activity level
Fresh food > .95
- most spoilage up to .9
< .9 water activity - most bacteria/yeasts cannot grow but molds can
< .8 only Xerophiles (dry, low osmolarity), Osmophiles (high osmolarity, high sugar) and Halophiles (high salt) can grow
Ex. S. aureus can grow at > .83
Psychrophile vs. psychrotrophs
Safe temps
Pathogens which grow at 4.5°C
Safest cold temp
Psychrophiles grow best at low temp
Psychrotrophs can grow at low temps
Keep food below 4.5°C and above 60°C
4.5°C pathogens: Yersinia enterocolitica, Listeria monocytogenes, Clostridium botulinum
- but microbes can survive at 4°C, just can’t grow
Only at -20°C the water activity is .82 and most microbes cannot grow
pH and microbial growth
Lactic acid bacteria can grow at 4 pH
- Few bacteria grow below 4 pH
Many yeasts/molds grow below 4 pH
Oxygen restriction inside food packaging
Restricts growth of aerobic bacteria yeasts and molds
Reduces oxidation of foods
Swelling of packaging (cans, vacuum packaging or MAP) –> don’t eat, implies growth of aerobic organisms
Microbes associated with high fat/protein foods
Microbes associated with higher carbohydrate foods
Bacteria and molds - yeasts cannot
Bacteria, yeasts and molds
Food poisoning/intoxication vs. food infections
Intoxication: caused by microbial toxins and usually symptoms appear quickly
Food infection: Microbes multiply in host and symptoms take longer to develop
- illness can be due to toxins or tissue damage
Dose vs. time is what determines severity - fresh foods have pathogens but in low quantity
Top 10 causes of food-borne disease
1) Leaving cooked foods at room temp or storing foods in large containers
2) 12h between prep and consumption
3) Infected person handling food
4) Inadequate reheating
5) Improper hot handling (too low temp)
6) Contaminated raw ingredients
7) Foods from unsafe sources
8) Improper cleaning of equipment
9) Cross contamination between raw-cooked foods
10) Inadequate cooking
Botulism type, symptoms, prevention and risk areas
Food poisoning AB-type neurotoxin from Clostridium botulinum
10% mortality from paralysis, cardiac/respiratory failure
Toxin destroyed by cooking
Risk areas: canning, non-reheated processed foods
Staphylococcal type, symptoms, prevention and risk areas
Type: food poisoning, enterotoxin from some strains of S. aureus
- 40% of food poisoning
Symptoms: nausea, vomiting and diarrhea after 1-6 hours
Toxin NOT destroyed by cooking
Risk area: food in large quantities then left at room temp, salted room temp foods (halotolerant)
Salmonella enterica type, symptoms, prevention and risk areas
Type: food infection, zoonosis
- 2000 serotypes in many mammals, birds and reptiles
Symptoms: grows in GI (most often Enteritidis and Typhi) causing nausea, vomiting, fever, diarrhea for 4-7 days
- invasion and destruction of intestinal epithelium
Cooking kills it
Risk areas: uncooked or slightly cooked foods or cross contamination
- requires time to multiply in food to 10^5-10^8
E coli O157:H7 type, symptoms, prevention and risk areas
Type: food infection which produces AB exotoxin, fecal coliform undetected bc it grows at 44.5°C
Symptoms: bloody diarrhea from damage to underlying mucosal tissues of GI
- toxins can travel to kidney –> hemolytic uremic syndrome and acute renal failure
- shiga-like toxin which inhibits protein synthesis
Cooking kills E coli
Risk areas: undercooked beef or beef left out
Alice Evans
Demonstrated in 1917 that raw milk could cause disease and that pasteurization could be used to avoid this
1930 milk pasteurization was adopted as policy as a result of her work
Pasteurization subjects and types
Dairy products, liquid egg, alcohol, fruit juice
LTLT: 30 min at 62.8°C (poor taste, cheap)
HTST: 15 sec at 71.7°C for drinking milk
UHT: 2 sec at 141°C long shelf life at room temp
LTLT = HTST in safety
Time/temp affected by protein, fat and sugar content in food
Canning temperatures and concept
Heat food inside closed container to create anaerobic environment
For acidic foods: 100°C
For low acid foods: 121°C
12D process: temp/time must kill 10^12 spores of Clostridium botulinum
Types of irradiation
For reducing contamination of fresh foods
Radappertization: kill all microorganisms
Radicidation: kill specific microorganisms
Radurization: reduce overall contamination
