3.1.1 Micro-organisms and Enzymes Flashcards
What are micro-organisms?
tiny organisms found in many places that can spoil foods. also known as microbes. yeast, moulds and bacteria are types of this
How is food spoilt?
contamination of yeasts, moulds or bacteria and contaminates with their waste products (toxins they produce)
enzymic activity can spoil food + ripen fruit and veg
What conditions do micro-organisms need for growth?
yeast, moulds and bacteria require:
food, moisture, warmth, time and correct pH
Why is food a condition for micro-organism growth?
nutrients are needed for growth
How can you prevent growth and multiplication of micro-organisms in food?
prevent contact with food and keep it covered
Why is moisture a condition for the growth of micro-organisms?
water is needed for all biological processes. if water is removed they cannot grow/multiply
How and why might you remove moisture from a food?
drying: adding high concentrations of sugar/salt - the water from cells are removed by osmosis
in order to prevent micro-organisms to grow/multiply
Why is warmth a condition for the growth of micro-organisms?
if too hot the micro-organisms will be destroyed, if too cold their multiplication slows down until it stops (become dormant)
the ideal temp is 37 degrees celcius
How to control micro-organism growth/multiplication by temperature?
cook food thoroughly at high enough temperature. cook at least to 75 degrees celcius to kill most microbes.
don’t leave food out in warm places. cool cooked and left over food must be refrigerated quickly and not left out. refrigerate between 0-5 degrees celcius or freeze -18 degrees celsius or below.
Why is time a condition for the growth of micro-organisms?
bacteria multiply every 10-12 minutes in the right conditions by binary fission
How to control the growth/multiplication of micro-organisms through time?
cook and cool foods thoroughly and use within “use by date”/ expiry date
Why is pH level a condition for the growth of micro-organisms?
right amount of acidity/alkalinity (pH) needed. if too much of one they cannot grow.
How can you prevent the growth of micro-organisms through pH level?
preserving food in vinegar is a method of preventing multiplication
vinegar is pH 2-3 (strongly acidic)
What are yeasts?
single celled fungi that reproduce by “budding”
What is ‘budding’?
the yeast cells grows a bud that becomes bigger, until it it breaks off and becomes a new yeast cell
How can yeasts grow?
with oxygen (aerobic yeast) or without oxygen (anaerobic yeasts)
in high concentrations of sugar + salt (jam, honey, chutney)
grown best in warm conditions (25-29 degrees)
can grow at refrigerator temps (0- below 5 degrees)
What kind of foods do yeasts prefer?
most, acidic foods (eg. oranges)
What temperature are yeasts destroyed at?
55 degrees celcius
What are moulds?
tiny fungi that produce thread like filaments that help the mould spread around the food
In which foods do moulds grow in?
foods with high sugar and salt concentrations
fairly dry food (like hard cheese)
often breads and bakery products
In which temperatures do moulds grow in?
grow best between 20-30 degrees
can grow at refrigerator temps (0 - below 5 degrees)
How can mold growth be sped up?
high humidity and fluctuating temperatures
What must you not do with foods with moulds?
eat them. even if scraped off, they can spread harmful substances deep into the food
What is bacteria?
single-celled micro-organisms
What groups can bacteria be divided into?
harmless bacteria, pathogenic bacteria and food spoilage bacteria
Where can bacteria be found?
everwhere around you - skin, food, water, soil, air etc
What do pathogenic bacteria do?
these are harmful and can cause food poisoning
What do food spoilage bacteria do?
they cause food to decay - to smell and lose its texture + flavour
What are the conditions for growth of bacteria?
warmth (body temp 37 degrees)
moist conditions on neutral foods with protein
How do bacterias reproduce?
binary fission: when one bacterium divides into two cells
How can bacterial growth be slowed/prevented?
storing food in fridge
cooking perishable food quickly (90 minutes before refrigerating)
reheating leftovers to 75 degrees only once
high concentration of salt/sugar/acid
What are the ideal conditions for bacterial growth and what are these types of food?
foods with moisture, high protein content, neutral pH, in warm environment
foods with these conditions that you can eat without cooking are known as high risk foods
What are some high risk foods?
cooked meat and poultry
cooked meat products like gravy, soup, stock
milk and eggs + their dishes
shellfish like mussels, crabs, lobsters
cooked rice
What are enzymes?
biological catalysts made from proteins to speed up chemical reactions
What do enzymes do?
cause browning in foods that are bruised/cut open - known as enzymic browning
they cause meat + fish tissues to break down once animal is killed
How is enzymic action controlled?
by causing them to denature through heat or acids
What is blanching?
heating food in boiling water for a short time to destroy enzymes before plunging it in iced water to stop the cooking process
When can enzymes still be active?
at freezer temperatures of -18 degrees of below
What can be used to prevent enzymic browning?
acids such as lemon juice. the acid denatures the enzymes so they become inactive (due to acidic pH)
What is sterlisation?
the complete destruction of all microbes in food processing
