Lecture 4: Spoilage/Pathogens
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How do yeasts reproduce?
• Budding 2. Fission
Name and describe the two different possible life stages of bacteria
• Vegetative cells (Normal organism) • Vegetative pathogen - active, growing form; Easier to kill • Growing or able to grow • Spores - When conditions are poor; harder to kill • Not able to grow - lays dormant until conditions are ripe (100s of years) • Resistant to heat, cold, drying (survive pasteurization) • Will germinate and grow under ideal conditions • eg: C. botulinum, Bacillus
Name and describe the growth factors of pathogens
1. Food • Water • Source of energy (food) - CHO, PRO; Less common starches & cellulose • Source of nitrogen (amino acids) • Vitamins and related growth factors • Minerals 2. Acidity - Majority of foods are <7pH • Bacteria - grow in 7-9pH range • Molds cover widest range - 2-12pH • Yeast is middle 3. Time • 2hr Danger Zone (40-140 F) • Spoilage organisms may grow slowly over the shelf life of food (months to years) 4. Temp • Majority organisms are mesophiles (50-122 F) • But are organisms that can grow from 14-194 F 5. Oxygen 6. Moisture/ Water Activity • Influenced by the presence of solutes (salt, sugar) • Does not correlate with moisture • >.85 Aw
What is the relationship between spoilage and foodborne illness?
Spoilage - Microorganisms cause an undesired change to the food’s smell, taste, appearance, texture; No human health risk • Yeast in juice • Mold on cheese & bread • Bacteria - spoiled milk, sulphur-y smell, swollen packaging Foodborne Illness/ Pathogenic - Microorganism causes illness • Public health hazards
Describe Clostridium botulinium
• Anaerobic • Spore forming • Produce toxin- botulin (same toxin as Botox) • Most common foods: - home-canned goods - low acid foods (i.e. asparagus, beets, corn) - Honey (infant) • Has to process in 121oC to kill both spores and bacteria cells.
Describe Escherichia coli
• Facultative anaerobic • Non-spore forming • Produce toxin - shiga food vehicles: meat, fresh produce - exist in all warm blood animals’ intestine, feces and raw meat contamination • Bacteria cells is easy to kill (71oC but spores are heat resistant 100oC)
Describe Listeria monocytogenes
• Facultative anaerobic • Non-spore forming • Pregnant women need to watch out for it.
Describe Salmonella
• Facultative anaerobic • Non-spore forming • All strains are pathogenic • Poultry and eggs are most important carrier • Killed by heat treatment (72oC).
If a food contains 24,000 CFU/mL, how many serial dilutions you have to make in order to get ideal plate count.
Goal is to get 30-300 CFU/ml in order to accurately count bacteria. Dilutions are by factors of 10, so that means you want to get the 24,000 per sample down to 240 (to fit within the 30-300 parameters). So in order to do that, you move the decimal (or divide by 10) two times. Therefore, you need to do two dilutions of factors of 10