3.1.1 Micro-organisms and Enzymes

Question 1

What are micro-organisms?

Answer 1

tiny organisms found in many places that can spoil foods. also known as microbes. yeast, moulds and bacteria are types of this

Question 2

How is food spoilt?

Answer 2

contamination of yeasts, moulds or bacteria and contaminates with their waste products (toxins they produce)
enzymic activity can spoil food + ripen fruit and veg

Question 3

What conditions do micro-organisms need for growth?

Answer 3

yeast, moulds and bacteria require:
food, moisture, warmth, time and correct pH

Question 4

Why is food a condition for micro-organism growth?

Answer 4

nutrients are needed for growth

Question 5

How can you prevent growth and multiplication of micro-organisms in food?

Answer 5

prevent contact with food and keep it covered

Question 6

Why is moisture a condition for the growth of micro-organisms?

Answer 6

water is needed for all biological processes. if water is removed they cannot grow/multiply

Question 7

How and why might you remove moisture from a food?

Answer 7

drying: adding high concentrations of sugar/salt - the water from cells are removed by osmosis

in order to prevent micro-organisms to grow/multiply

Question 8

Why is warmth a condition for the growth of micro-organisms?

Answer 8

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

Question 9

How to control micro-organism growth/multiplication by temperature?

Answer 9

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.

Question 10

Why is time a condition for the growth of micro-organisms?

Answer 10

bacteria multiply every 10-12 minutes in the right conditions by binary fission

Question 11

How to control the growth/multiplication of micro-organisms through time?

Answer 11

cook and cool foods thoroughly and use within “use by date”/ expiry date

Question 12

Why is pH level a condition for the growth of micro-organisms?

Answer 12

right amount of acidity/alkalinity (pH) needed. if too much of one they cannot grow.

Question 13

How can you prevent the growth of micro-organisms through pH level?

Answer 13

preserving food in vinegar is a method of preventing multiplication

vinegar is pH 2-3 (strongly acidic)

Question 14

What are yeasts?

Answer 14

single celled fungi that reproduce by “budding”

Question 15

What is ‘budding’?

Answer 15

the yeast cells grows a bud that becomes bigger, until it it breaks off and becomes a new yeast cell

Question 16

How can yeasts grow?

Answer 16

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)

Question 17

What kind of foods do yeasts prefer?

Answer 17

most, acidic foods (eg. oranges)

Question 18

What temperature are yeasts destroyed at?

Answer 18

55 degrees celcius

Question 19

What are moulds?

Answer 19

tiny fungi that produce thread like filaments that help the mould spread around the food

Question 20

In which foods do moulds grow in?

Answer 20

foods with high sugar and salt concentrations
fairly dry food (like hard cheese)
often breads and bakery products

Question 21

In which temperatures do moulds grow in?

Answer 21

grow best between 20-30 degrees
can grow at refrigerator temps (0 - below 5 degrees)

Question 22

How can mold growth be sped up?

Answer 22

high humidity and fluctuating temperatures

Question 23

What must you not do with foods with moulds?

Answer 23

eat them. even if scraped off, they can spread harmful substances deep into the food

Question 24

What is bacteria?

Answer 24

single-celled micro-organisms

Question 25

What groups can bacteria be divided into?

Answer 25

harmless bacteria, pathogenic bacteria and food spoilage bacteria

Question 26

Where can bacteria be found?

Answer 26

everwhere around you - skin, food, water, soil, air etc

Question 27

What do pathogenic bacteria do?

Answer 27

these are harmful and can cause food poisoning

Question 28

What do food spoilage bacteria do?

Answer 28

they cause food to decay - to smell and lose its texture + flavour

Question 29

What are the conditions for growth of bacteria?

Answer 29

warmth (body temp 37 degrees) moist conditions on neutral foods with protein

Question 30

How do bacterias reproduce?

Answer 30

binary fission: when one bacterium divides into two cells

Question 31

How can bacterial growth be slowed/prevented?

Answer 31

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

Question 32

What are the ideal conditions for bacterial growth and what are these types of food?

Answer 32

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

Question 33

What are some high risk foods?

Answer 33

cooked meat and poultry cooked meat products like gravy, soup, stock milk and eggs + their dishes shellfish like mussels, crabs, lobsters cooked rice

Question 34

What are enzymes?

Answer 34

biological catalysts made from proteins to speed up chemical reactions

Question 35

What do enzymes do?

Answer 35

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

Question 36

How is enzymic action controlled?

Answer 36

by causing them to denature through heat or acids

Question 37

What is blanching?

Answer 37

heating food in boiling water for a short time to destroy enzymes before plunging it in iced water to stop the cooking process

Question 38

When can enzymes still be active?

Answer 38

at freezer temperatures of -18 degrees of below

Question 39

What can be used to prevent enzymic browning?

Answer 39

acids such as lemon juice. the acid denatures the enzymes so they become inactive (due to acidic pH)

Question 40

What is sterlisation?

Answer 40

the complete destruction of all microbes in food processing