Lecture 8 - Food Microbiology
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What are the types of microbes in our food?
Bacteria/Virus/Fungi/Protozoa
What are some common shapes of bacteria?
Round (Cocci) Rod-Shaped (Bacilli) Curved-Shaped (Spirilla)
What is the purpose of gram staining?
Bacteria Identification
What are gram positive cells?
Cells have a larger and more highly cross-linked peptidoglycan
What are gram negative cells?
Cells that do not possess a peptidoglycan layer
What are the factors that affect microbial growth?
• Food composition/ Availability of nutrients • pH • Availability of oxygen • Temperature
What is the minimum water activity required for bacteria growth?
0.60
Which type of bacteria has a higher minimum water activity? Gram positive or gram negative?
Gram Negative
Do bacteria require higher or lower water activity and pH for growth compared to yeast and moulds?
Higher
What is the minimum number of bacteria cells per gram in order to cause food spoilage?
10 million cells per gram
What are food spoilage microorganisms?
Microorganisms that produce undesirable aromas, colour defects and slime formation and renders a food to be unsafe for consumption
What are some of the causes of food associated outbreaks?
Improper storage temperatures Poor personal hygiene Inadequate cooking temperatures Cross-contamination Contaminated raw materials
What are some of the hurdles that inhibit the growth of microbes?
High temperature (for psychrophiles) Low temperature (for thermophiles) Reduce water activity Addition of preservatives (sucrose, sodium chloride, lactic acid, hydrogen peroxide, nitrates)
What is the microorganism responsible for the fermentation of barley to make beer, ferment grapes to make wine and to bake bread?
Saccharomyces Cerevisae
What is the microorganism responsible for pickling cucumbers?
Lactobacillus plantarum
What are some examples of food spoilage microorganisms?
Lactobacillus (lactic acid formation), Enterobacter(slime formation)
What are some examples of pathogenic microorganisms?
Shigella, Salmonella, E.Coli (O157:H7)
What are the characteristics of Salmonella? What are its symptoms and what is it commonly found in?
Gram-negative, rod-shaped, facultative anaerobic Fever, diarrhoea and abdominal cramps Commonly found in eggs and milk
What are the characteristics of E.Coli (O157:H7)? What are its symptoms and what is it commonly found in?
Gram-negative, rod-shaped, facultative anaerobic Urinary tract infections and diarrhoea Commonly found in raw food, raw milk
What are the characteristics of Listeria Monocytogenes? What are its symptoms and what is it commonly found in?
Gram-positive, rod-shaped, facultative anaerobic Fever, Muscle Ache, Diarrhoea Commonly found in raw milk
What are the characteristics of Vibrio? What are its symptoms and what is it commonly found in?
Gram-negative, comma-rod shaped, facultative anaerobic Watery diarrhoea, vomiting and rapid heart rate Commonly found in raw or undercooked seafood