pasteurisation Flashcards
1
Q
definition of pasteurisation
A
heat treatment to kill bacteria and MO to increase shelf life
2
Q
what is pastuerisation
A
heating to a specific temp then radpily cooling it
3
Q
types of pastuerisation
A
- LTLT = low temp, long time
- HTST = high temp, short time
- UHT = ultra high temp
4
Q
LTLT
A
63oC
30 mins
5
Q
HTST
A
72oC
15 seconds
6
Q
UHT
A
135oC
2-5 seconds
7
Q
how to know if pasteurisation was successful?
A
- temperature and time control
- phosphatase test
- microbiological testing
- homogeneity
- taste and smell
8
Q
temperature and time control
A
accurate monitoring: ensure milk reaches required temperature
9
Q
phosphatase test
A
alkaline phosphatase (naturally present in raw milk) is destroyed at lower temperatures than most pathogenic bacteria
10
Q
microbiological testing
A
- bacterial plate count - after pasteurisation test for presence of bacteria
- coliform test - (faecal contamination)
11
Q
homogeneity
A
visual inspection - properly pasteurised shouldn’t clump or separate
12
Q
HTST principle
A
- cold raw milk 4oC into plant
- goes to regenerative head, passing through cold plates (57-68oc)
- milk goes to heating part = 72oC
- hot milk goes through holding tube (takes 15s) - pasteurised milk goes back to regenerative part, warming incoming cold milk - coolingg pasteurised milk to 32oC
- cooling part reduces milk to 4oC
13
Q
disadvantage of HTST
A
- increase temp inactivates enzymes, increases risk of spoilage
- increase temp = discolouring of milk
- increase temp, alters protein structure
14
Q
UHT
A
- heating milk/cream to 135-150oC for 1-2s then chilling
- usually sterilised too
- shelf life of 9 months without fridge
