∙ Fridge
∙ Colorimeter
Method:
Pour a carton of UHT milk into a 10ml beaker, using a 10cm3 sterile pipette draw out 10cm3 of milk and release the milk into a test tube, repeat this procedure for three test tubes. Once the milk is in the test tubes add a drop of 1% methylene blue concentration to all the milk solutions, with a cork securely fixed on the test tubes thoroughly shake the mixture a blue precipitate should form. Repeat these steps for the pasteurized milk pour a carton of pasteurized milk into a 10ml beaker, using a 10cm3 sterile pipette draw out 10cm3 of milk and release the milk into a test tube, repeat this procedure for three test tubes. Once the milk is in the test tubes add another 1% methylene blue concentration into the milk solution, with a cork securely fixed on the test tube thoroughly shake the mixture a blue precipitate should form. Before concluding make sure that all the methylene blue milk solutions are left in their appropriate conditions for the first day. For one of the UHT leave one colorimeter tube in an incubator at approximately 27 degrees, another at room temperature and the last in a refrigerator, repeat this procedure for the pasteurized milk. The next day using a pipette draw out a drop of the methylene blue and milk solution and release this into a colorimeter tube, using a measuring cylinder measure 5cm3 of distilled water and use this to dilute the methylene blue and milk solution. Meanwhile set up the colorimeter by selecting a suitable filter, a red filter would be the most suitable when analysing a blue solution, because the filter will absorb all light frequencies except blue. After selecting a suitable filter, pour water into a colorimeter tube and put it into the colorimeter, then press the reference (“R”) button to zero the reading of the colorimeter, water is suitable for the reference because water doesn’t absorb any light. Place the first colorimeter tube with the methylene blue and milk solution in the colorimeter and press the test (“T”) this should give a reading for the solution, repeat this for the rest of the other five solutions, once the readings have been recorded, discard of the diluted solutions and leave the original solutions in their appropriate conditions for another day. The next day repeat the same dilution procedure remembering to use the same colour filter, place all the diluted solutions in the colorimeter and take a recording of the readings, discard of the diluted samples and store the original samples in their appropriate conditions and leave for one more day. By the third day the colours should become noticeably different in contrast, repeat the same dilution procedure once again, remembering to use the same colour filter, place all the diluted solutions in the colorimeter and take a recording of all the readings, then discard of all the diluted solutions. If more readings need to be taken the original solutions can be left for another day and recorded to a get more accurate average of all the readings, if the solutions are no longer needed then all the original solutions may be discarded. (Reference 4)
Prediction:
My prediction is that the pasteurized milk will produce more enzymes than UHT milk, and will therefore decompose at a faster rate than the UHT milk making its shelf life much shorter than that of UHT. Furthermore I believe that the three conditions have a big impact on the speed of the decomposition, both types of milk will decompose faster under higher temperatures, the milks in the incubator will decompose at the fastest rate, then the mil at room temperature, then the milk in the refrigerator.
Scientific reasoning:
Milk is an opaque white solution made up of mainly water, lactose, soluble proteins, minerals, vitamins, milk fat, acids and enzymes. UHT milk is heated at high temperatures for a short period of time before it is left to cool down. The heating of the milk kills most vegetative micro organisms; it inactivates some of the soluble proteins, furthermore it minimizes a lot of the chemical reactions such as the browning reaction between sugar and proteins increasing the shelf life of the milk. However pasteurized milk is heated at a moderate temperature compared to UHT, the heating kills micro organisms and vegetative organisms, and a lot of the bacteria in the milk, furthermore pasteurized milk has higher concentration of bacteria compared to that of UHT milk (Reference 5 ), because the pasteurized milk has more bacteria than the UHT milk, the bacteria and enzymes acts as the biological catalysts and speed up the rate at which the milk decomposes therefore the pasteurized milk has a shorter shelf life and spoils faster than the UHT milk with a lower concentration of bacteria which has a longer shelf life. Furthermore the change of conditions affects the rate at which the milk decomposes. The higher the temperature the more energy is provided, and the faster the reaction of the decomposition occurs, therefore the milk samples left in the warm conditions will spoil first, then the room temperature, and finally the samples left in the fridge.
The higher the concentrations of enzyme and substrate molecules, the more higher the chance of successful collisions so the overall reaction is speeds up, however the lower the concentration the less frequent the enzyme and substrate make successful collisions, so the overall reaction is slower.
(Reference 6)
The higher the temperature the more kinetic energy provided for molecules to collide and to successfully react. (Reference 7)
Analysis of variables:
Independent variables: In this experiment the temperature was the independent variable, the temperature was varied to see what effect it would have on the milk.
Dependent variable: In this experiment the methylene blue and milk solution was the dependent variable by leaving the solutions in a variety of conditions, in the incubator, at room temperature, and in the fridge, we are able to observe and analyse how temperature affects the rate at which the milk spoils. Using methylene blue dye the more enzymes produced by the increase in temperature, the clearer the dye would go until it went colourless, using a colorimeter to help collect accurate readings an results, by measuring the absorbance, the more enzymes that was produced the clearer the solution would go and the lower the absorbance readings, the absorbance of the solution was measured over a period of three days.
Controlled variables:
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The six solutions of milk were all made on the same day so the rate at which the milk spoilt stayed the same.
- The same milk type was used for each of the solutions.
- Each of the solutions was repeatedly left in the same conditions they originally were in.
- All milk solutions were diluted with the same volume of water.
Results:
