Site pages
Current course
Participants
General
18 February - 24 February
25 February - 3 March
4 March - 10 March
11 March - 17 March
18 March - 24 March
25 March - 31 March
1 April - 7 April
8 April - 14 April
15 April - 21 April
22 April - 28 April
13. Determination of microbiological quality of food by dye reduction test
13. Determination of microbiological quality of food by dye reduction test
Dye reduction test is a simple and easy to perform enzymatic test useful for determining the microbiological quality of food samples such as milk. A milk sample containing large population of actively metabolizing microorganisms lower dissolved oxygen because of vigorous growth of microorganisms thereby lowering oxidation-reduction potential in the sample. The dye methylene blue, a redox indicator, becomes reduced in an anaerobic environment and loses its color. Thus, there is direct relation between the length of time required for reduction and the number of bacteria present. The speed at which methylene blue becomes colorless following addition to sample indicates quality of milk. The shorter the reduction time, lower the quality of milk. Based on dye reduction test four grades of milk quality is recognized.
Decolonization Time |
Approx. no of microorganisms/ml |
Quality grade |
0- 20 minutes |
> 2 x 107 |
Very bad |
Materials required
1. Sterile test tubes with stopper
2. Milk sample
3. Metylene blue solution (1: 25,000)
4. Pipettes (10ml, 1ml)
Procedure