Transcript document

Micro-organisms
Aim
To be able to test milk to see how fresh it is
Context
When milk is collected from farms it is
then transported in tankers. It is
important that the milk collected is fresh
or it could contaminate the whole tanker.
A farmer needs to ensure that his milk is
fresh enough and the Milk Marketing
Board can help with this by testing his
milk.
Context
As milk gets older bacteria grows in it.
The bacteria respire using up oxygen and
lactose (sugar in milk) turning it into
carbon dioxide and lactic acid (makes
milk taste sour). Resazurin is a chemical
which detects the amount of oxygen
present by changing colour. (click here)
Results
Colour of sample
Quality of milk
Blue (no colour
change)
Blue to mauve
Excellent
Mauve to pink
Fair
Pink to pale pink
Poor
White
Bad
Good
Risk Assessment
Risk:
Hazard:
Control Measure:
Equipment
Method: Testing milk
1. Label test tubes S (sample from farm), F (fresh milk), 1 (1
day old), 2 and 3.
2. Using a pipette add 1cm3 of Resazurin solution to each tube
3. Using the measuring cylinder place 5cm3 of fresh milk in the
tube labelled S and put a stopper in it.
4. Repeat with the fresh milk in tube F, 1 day old milk in tube
1 etc
5. Put all of the test tubes into a rack and place rack into a
water bath for 30mins
6. Record the colour differences in a suitable table of results
Results table
Test tube
Sample (S)
Fresh (F)
1 day old (1)
2 days old (2)
3 days old (3)
Colour of
sample
Quality of
milk
Analysis and Evaluation
Aim
To be able to explain what our results
show and evaluate our experiment.
Analysis
My results show that the older the
milk……………………
These results happened because
…………………
The milk sample taken from the farmer was
of ……………………. quality
Evaluation
My experiment went…
I had problems with … because…
To improve my experiment I could…
My results would be more reliable if I…
I did/did not have odd results……….
This was because……………….