Aim: To investigate and compare the amount of proteins, lipids and carbohydrates in three different types of milk; soy milk, skim (or fat free) milk and fresh milk.
* Skim milk will have less fat compared to fresh milk.
* Soy milk will have more proteins than skim and fresh milk.
* Fresh milk will have a balanced amount of proteins, carbohydrates and lipids.
Variables that will be kept constant:
* Volume of samples
* Quantity of milk
* Types of milk
* Impurities in milk
* Skim milk and whole milk come from animals.
* Soy milk comes from plants.
* 15 grams of soy milk (powder form) mixed with 500ml of water
* Skim milk (fat free)
* Fresh milk
* Benedict’s solution
* Sodium hydroxide
* Copper sulphate
* Distilled water
* Piece of fat
* Test tubes
* Filter paper
* Glass rod
* Clamp stand
* Bunsen burner
* Heat proof mat
In order to accomplish our aim, testing for proteins, carbohydrates and lipids had to be done:
Testing for proteins:
1. Pour 1.3 cm3 of fresh milk in a test tube.
2. Add five drops of sodium hydroxide and shake slightly. Add five drops of copper sulphate to the fresh milk. Do not shake.
3. Observe and record any change in the colour of the milk. (If proteins are present the solution will turn purple).
4. Repeat the procedure with 1.3 cm3 of skim milk and with 1.3 cm3 of the soy milk solution.
5. Observe all three samples and see which one turned the most purple. Record the results and scale them from 1 to 3 to be able to know which milk had the most amount of proteins (one for the least amount and three for the largest amount).
Testing for carbohydrates (reducing sugars):
1. Pour 2 cm3 of fresh milk into a test tube.
2. Add 2 cm3 of Benedict’s solution to fresh milk.
3. Pour water into a separate beaker and heat the water using a Bunsen burner.
4. Place the test tube containing 1.3 cm3 of milk and the Benedict’s solution in the beaker with hot water.
5. Observe and record any change in colour of the milk. If reducing sugars are present the milk should turn brown-orange.
6. Repeat the procedure with of skim milk and with soy milk solution.
7. Observe the three samples and see which one turned the most brown-orange. Record the results and scale them from 1-3 to be able to know which milk had the most amount of carbohydrates (one for the least amount and three for the largest amount)
Testing for lipids:
1. Pour 1.3 cm3 of fresh milk into a test tube.
2. Add 0.65 cm3 of alcohol to the milk.
3. After separates into to layers, filtrate the milk using a funnel and filtrate paper.
4. Pour the filtrated solution into 1.3 cm3 of water.
5. Observe and record any changes in the clearness of the water. If lipids are present the water should turn cloudy.
6. Repeat the procedure with 1.3 cm3 of skim milk and 1.3 cm3 of the soy milk solution.
7 . Observe all three samples and scale the cloudiness of the solution from 1-4 (one being the least cloudy and five being the most cloudy)
In order to have something to compare the tests with, different controls were used:
For the protein test, liver was used because it is made entirely of proteins.
1. Mix 5 cm3 of liver and 15 cm3 of water
2. Filtrate the solution
3. Put 1.3 cm3 of the solution obtained in a test tube
4. Add five drops of sodium hydroxide.
5. Add five drops Copper Sulphate.
6. Observe and record the colour change (if any). This colour revels the presence of proteins.
For the Carbohydrates (reducing sugars) test, glucose was used because glucose is the most common monosaccharide:
1. Make a mixture of 2 cm3 of glucose and 2 cm3 of water.
2. Pour the mixture into a test tube and add 2 cm3 Benedict’s solution.
3. Place it in hot water.
4. Observe and record the colour change (if any). This colour reveals the presence of reducing sugars.
For the Lipids test oil was used because oil is a lipids.
1. Add 1.3 cm3 of alcohol to 1.3 cm3 of oil.
2. Filtrate the solution.
3. Pour filtrated solution into 1.3 cm3 of water.
4. Observe and record any change in the water. This change reveals the presence of lipids.
Test for Carbohydrates
Table showing the color change for the types of milk and the control
Types of milk and control
Time for the change
Most amount of carbohydrates (one for the least amount and three for the largest amount)
Test for Proteins
Table showing the color change for the types of milk and the control
Types of milks and control
Very light purple
Most amount of proteins
(one for the least amount and three for the largest amount)
Test for lipids
Table showing the types of milk and the control reaction rates
Type of Milk
Oil (1.5 cmï¿½ )
Conclusion and Evaluation:
It can be concluded that, skim milk has the less lipids compared to fresh milk, which proves its efficiency in its use of diets. This is because skim milk, is the result of the process of separation of milk. As well, It can be concluded that Soy milk had less amount of proteins than skim and fresh milk which proves that the other two types are better sources of proteins.
Fresh milk has a balanced amount of protein, carbohydrates and lipids as it always located itself on the numbers one or two of the scales, which proves that it had a fair amount of substances compared to the other types of milks. As the results where divided in the three substances (carbohydrates, proteins and fats) it is fair to divide the evaluation of procedures in parts:
Lipids: A weakness was that the time for the solutions to change color should have been taken, so it will be easier to rate the reaction as the colours often are alike and difficult to compare. For the control, (liver) the solution containing the liver should have turned much more purple (darker) because it had more soluble protein in it, but in this case it was diluted with 15 cm3 of water. For a further experiment it must be diluted in less water.
For the testing of Carbohydrates, for the control of this test, first, table sugar was used but the result was a green colour. This colour was generated because table sugar is sucrose. Therefore, pure glucose was used, which gave a perfect control for the experiment. This test was done three times to get acurrent results, even more testing will give more acurrent results.
For the testing of lipids, first, a piece of animal fat was used as the sample, but as it could not be proof to be pure fat, oil was used instead. Also, when the milk was separated into fat and water, the quantity used was small, so it made it hard to see the thin layer of fat formed. Therefore, this think layer was absorbed by means of a dropper. More quantity of every substance should have been used for clearer results. Also, it was complicated to have acurrent results, as it is difficult to measure the cloudiness of the solution.
In further experiments milk temperature has to be controlled as it was different (this is because for example fresh milk had to be kept refrigerated to avoid souring). The temperature of the milk might have varied, we did not control this variable at all and this might have affected the result of the experiment. We could have taken the temperatures of the milks or even heat them so that they were all at the same warmth. This way the results could be more precise helping us reach a consistent conclusion
It should be considered that the fresh milk used had been actually pasteurized and therefore the bacteria in it was killed through the UHT test (ultra height temperature, where milk has been held at 132ï¿½C for 2 seconds) On the other hand, fresh milk, straight from a healthy cow contains few bacteria.