Lecture 1
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What are the 3 main microorganisms in food?
Mould Bacteria Yeast
What is yeast?
One cell microorganisms Reproduced by budding Grow best in the presence of: -moisture -O2 -Sugar -Acidic pH Ferments sugar into alcohol and CO2
What food is yeas important in?
Bread Wine Beer
What is a mould?
Multicellular and filamentous Reproduce by spores Grow on dry food, cereals, grains (unique to them) Can grow at room temp or cold temps
What food is mould important in?
Cheese and soy sauce
What are the different bacterial morphologies?
Cocci diplococci Sarcina Staphylcocci Streptococci Rods Vibrio
What are 2 important factors that are important to microbial growth?
Extrinsic Factors Intrinsic factors
What are extrinsic factors?
Depends ono the storage environment such as: • Temp • HUmidity • Envrionmental Gases(O2, CO2)
What are intrinsic factors?
Properties inherent to food to help protect them such as: • biological structure (skin, shell) • pH, water activity, anti-microbial compounds, nutrients
What are the 2 kinds of water activity?
Higher the free water the higher the water activity ○ Free water available for physical and chemical reactions ○ Bound water bound to sugars and not able to participate in andy chemical reactions
How can low water activity be brought about?
Dehydration Addition of Salt or sugar (binds water to make in unavailable)
What water activity do most fresh foods have?
0.96-0.99
Bacteria that causes food-born illness will grow on foods that have a water activity of what?
0.85 and above
What are the 3 temp categories that bacteria like to grow at?
Psychrophilic Cold Thermophilic >40C Mesophilic ~30C
How do we classify bacteria based on their need for O2?
Aerobic or Microaerophile (likes small % of O2) Anaerobic Facultative (can grow in presence or absence of O2)
What are spore formers?
Bacteria form spores around themselves to protect against harsh environment Can have dorment spores, activated in better conditions
In general what do molds require for growth?
O2
What conditions does yeast grow best in?
Aerobic
What is food spoilage?
Indicative of deterioration in taste, smell, sight and texture -deterioration of sensory products
How can spoilage occur?
Chemical reaction: oxidation of fats causes rancidity Physical change: bruising/dehydration Microbial growth
What are the typical indications of food spoilage?
Mold growth Gas Slime Off odour Off Flavour
What is the most common off odour ?
Smell of ammonia, sulphides and hydrogen sulphide -typical smell of eggs
What is the most common off flavour?
Acidic Bitter Not fresh
What is the most common off texture?
Slimy Mushy