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Science experiment Group 8 Determine the presence of microorganism in different brands of milk. Aim: To detect the presence of microorganism in milk by using methylene blue. Hypothesis: Methylene blue reacts to the lack of dissolved oxygen by turning translucent in milk when there is no dissolved oxygen in a sample. Apparatus: Test tubes, eye dropper, measuring cylinder, 3 brands of milk (Dutch Lady, Goodday, HL), methylene blue Procedure : 1. Prepare 2 test tubes. 2. Measure 10ml milk by using measuring cylinder and pour it into both test tubes. 3. Use eye dropper to measure 1ml of methylene blue and pour it into one of the test tubes. 4. The test tube with the methylene blue is test sample and the other which without methylene blue is for compare. 5. Pick up the test tubes and shake them so that the methylene blue is dissolved. 6. Place them about 3 days for observation. 7. Repeat step 1~6 for other two brands of milk at the same time. Result:
 Before the test
 After 3 days
Discussion : Milk contains carbohydrates, proteins, fats, salts and vitamins, its pH value is about 6.8, so it will be decomposed easily by microorganism. Conclusion : Methylene blue is an oxidation reduction indicator. In an anaerobic environment, it will be reduced to colorless. If there are bacteria in milk, which will inevitably lead to a reduction of dissolved oxygen, redox potential of milk samples is reduced. Hypothesis is accepted.

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