Preservation

Question 1

Give 6 ways to preserve food products

Answer 1

Drying
High temps - eg. Pasteurisation, Canning, Sterilisation, Ultra heat treatment
Freezing
Altering pH
Removal of oxygen 
Preservatives
Irradiation

Question 2

What is pasteurisation?

Answer 2

Pasteurisation is a method of heat treatment.
Kills harmful microorganisms and extends storage time
Used mainly on milk
Milk is pressed through plate heat exchanger heats it to 71 and holds it for 15 seconds and then is rapidly cooled to 10 degrees

Question 3

What is drying?

Answer 3

Removes water from food
Can be used on milk
Milk is heat treated, evaporated and sprayed into chamber of hot air causing the water to evaporate and milk to form powder

Question 4

What is canning?

Answer 4

Sealing food in air tight containers and heating to temps of 250 degrees to sterilise contents
Kills microorganisms to avoid poisoning and spoilage
Prevents recontamination
Some canning uses low ph or presence of salt of sugar as control

Question 5

What is sterilisation?

Answer 5

Heat treatment for longer time at higher temps than pasteurisation
Between 115 and 130 maintained for 10 to 30 minutes
Extends storage period
Milk and fruit juice
Slight caramelisation of milk
Put in glass bottles and sealed air tight which are then heat treated
Does not require refrigeration

Question 6

What is ultra heat treatment?

Answer 6

Very high temp to destroy all bacteria 
Extends storage
Steam raises temp to 145 for short time seconds
Cooled in sterile vacuum chamber 
Keep for months unrefrigerated
Airtight cartons
Only slight change in taste

Question 7

What is freezing?

Answer 7

Temperatures below 0 degrees stops microbial action
Various methods: immersion, plate, cryogenic and blast
Microorganisms cannot grow and multiply

Question 8

What 5 things are necessary to microorganism growth and survival?

Answer 8

Oxygen
pH
Water
Warmth
Food (proteins)

Question 9

Explain how microbial risk assessments are carried out

Answer 9

Sample is taken from one batch
Made into liquid solution
Smeared on agar medium
Left to incubate (sterile conditions)
When done placed under microscope
Colonies of microorganisms identified and counted using a clicker pen
If large quantities of pathogenic bacteria are found the product may be unsafe for human consumption and contaminated removed from circulation
Also used to calculate use by and sell by dates

Question 10

Name 3 types of microorganisms

Answer 10

Yeasts
Moulds
Bacteria

Question 11

What is a yeast and how does it affect food?

Answer 11

Break down sugar to produce ethanol and carbon dioxide known as fermentation
Used in bread making and brewing
Used for yeast extract spreads
Can cause spoilage in high sugar foods Eg fruit, jam
Found in air soil and skin of fruit

Question 12

What is a mould?

Answer 12

Used to produce specific flavours and textures eg. Blue cheese
Considered harmless
Produce heat resistant spores
Very high temps required to destroy spores
Can produce mycotoxins which are poisonous

Question 13

What is a bacteria?

Answer 13

Pathogenic bacteria cause food poisoning
Reproduce quickly
Thrive in variety of conditions and temperatures
Produce spores
Not easily detected
Used to make cheese and yogurt

Question 14

What is clostridium perfringens?

Answer 14

Found in soil, excreta, raw meat and insects
Multiplies during slow cooking
Found in gravy, cooked meat, pies
Have to cool food quickly so that spores do not germinate

Question 15

Give 5 ways of managing risk of bacteria and viruses

Answer 15

Cross contamination
Cleaning
Chilling
Cooking
Management

Question 16

How do you prevent cross contamination?

Answer 16

Personal hygiene
Cloths
Separating foods
Pest control
Maintenance
Physical and chemical contamination
Fridge handles
Light switches

Question 17

How can cleaning prevent microorganism growth?

Answer 17

Cleaning effectively
Clear and clean as you go
Cleaning schedules

Question 18

How can chilling prevent food contamination by microorganisms?

Answer 18

Chilled storage and display
High risk foods
Defrosting 
Chilling down hot food
Freezing

Question 19

How does cooking reduce the risk of bacteria and viruses?

Answer 19

Cooking safely
Foods that need extra care - meat eggs etc
Reheating temps
Hot holding temps
Ready to eat food

Question 20

How can management reduce risk of bacteria and virus?

Answer 20

Training and supervision/customers
Suppliers and contractors/ stock control
Product withdrawal and recall
Records of food traceability
Random sampling

Question 21

How can we prevent rancidity from occurring in production and storage of food products?

Answer 21

Using antioxidants absorb oxygen to stop development of free radicals and oxidative rancidity
Fats should be heat treated to kill microorganisms and inactive enzymes present to stop hydrolytic rancidity
Fat should be stored away from heat sources, light and traces of metal to prevent oxidative rancidity
Oil stored in glass lined containers as iron will initiate oxidative rancidity
Kept cool and free from air(oxygen)

Question 22

What nutritional effects does pasteurisation have on milk?

Answer 22

Not a lot
10% thiamin and vit b12
25% vitamin c

Question 23

What sensory effects does pasteurisation have on milk?

Answer 23

None

Question 24

What effect does UHT have on nutritional content of milk?

Answer 24

B and c may be affected because unstable at high temps but time is so short the content won’t be significantly reduced, similar to pasteurised milk

Question 25

What is the sensory effect of UHT on milk?

Answer 25

Homogenised so appear slightly thicker or creamy because fat globules are evenly spread in milk
Lactose partially caramelised slightly cooked flavour

Question 26

Effect of spray drying on nutritional content of milk?

Answer 26

Reduced fat and fat soluble vits because skimmed milk is used

Question 27

What is the effect of spray drying on the sensory qualities of milk?

Answer 27

When recombined with water does form a perfect solution so is powdery, bitty texture
Appears thinner in drinks

Question 28

What is the effect of evaporation on nutritional content of milk?

Answer 28

Lost about 60% vit C and 40% thiamine

Other nutrients concentrated due to loss of moisture

Question 29

What is the effect of evaporation on the sensory qualities of milk?

Answer 29

Milk is homogenised and sterilised in the can concentrated to about twice the density of original milk
Pronounced flavour
Tan colour due to reaction between lactose and protein when milk is sterilised

Question 30

Explain the use of preservatives in food manufacture

Answer 30

Keep food fresh for longer than normal
Extend shelf life and prevent growth of microorganisms causing food spoilage and lead to food poisoning
Sulfur dioxide and benzoic acid

Question 31

What is plate freezing?

Answer 31

Food produced in usual way and put in flat container usually cardboard
Container placed between flat hollow refrigerated metal plates which press tightly to pack
Method is slowed if air gap between food and plate
Less efficient than other methods

Question 32

What is blast freezing?

Answer 32

Ideal for irregular shaped foods
Large cabinet with fan to move air over the product
Moving air readily takes up heat and loses it again
Air is -25C or lower and moves at velocity 400m/min
Blast freezer generally batch system

Question 33

What is cryogenic freezing?

Answer 33

Very cold liquified gases such as nitrogen
Rapid method of freezing
Can cause thermal shock to some foods because of sudden contraction
Sprayed on conveyor belt
Good for soft fruit and prawns