Whole milk, semi-skinned milk and skimmed milk are the three milks, which are going to be used in this investigation. Before I can investigate the differences in the time of coagulation of the milks, I must understand how each milk differs to each other. This will affect the timings in which it will take for the milk to coagulate. An important factor to consider is fat content of the milks.
Semi skimmed milk
Semi skimmed milk has about half the fat content of whole milk (at least 1.5% fat, but not more than 1.8%). It has slightly more protein, calcium and some of the vitamins of whole milk. However it is lower in calories than whole milk and in the fat-soluble vitamins A and D, which are removed with the fat.
Skimmed milk
A very low fat milk (it contains 0.1% fat) skimmed milk looks and tastes less creamy than any other type of milk, because of the removal of the fat. It has slightly more protein and more of some the vitamins than whole milk, but less of vitamins A and D which are fat soluble and so removed with the fat.
Whole milk
Also known as full fat milk, this is milk that has not had its fat content altered. It has a fat content of about 4% and contains a range of nutrients and vitamins.
Enzymes
Vegeren is an enzyme, which is a substance known to speed up the process of a reaction. In this case it is to speed up the coagulation of milk. An enzyme molecule will change its shape to bind to the active site of a substrate molecule (milk) and then can be called a successive reaction, this is known as the lock and key mechanism. If the enzyme molecules are out numbered by the substrate molecules it is likely the reaction is slow because although all the enzyme molecules have binded to a substrate molecule, the substrate molecules are still in excess and require more enzyme to bind to the active sites. If the enzyme concentration is increased, the number of successive collisions is increased and therefore the rates is increased as well as yield. This will occur to a point where the enzyme molecules will out number the substrate molecules and therefore increasing the concentration of enzyme will cause no more effect.
Plan:
I intend to add the vegeren to the milks in separate syringes, and then leave the mixture for a set time. After a while the milk should have coagulated and I can then pull the plunger out of the syringe allowing the coagulated milk to drain out. During this time, a stopwatch will be used to time how long it takes for the milk to drain out of the syringe. Different concentrations of vegeren added to the milk will be used. The vegeren will be diluted using distilled water and measured using a measuring cylinder.
I think that the higher the concentration in vegeren added to the milk, the more the milk will coagulate in the set time and the longer it will take to drain the milk mixture from the syringe. Also the milk with the higher content of fat will coagulate more in the set time than the other milks with less fat content i.e. whole milk will clot more than skimmed milk as whole milk has 4% fat compared to skimmed milk which only has 0.1% fat.
Apparatus:
- Three clamp stands to hold the syringes face down
- Six 5ml syringes to hold the milk mixtures from which they will be drained.
- Five 100ml beakers to hold the milks, vegeren and mixtures.
- Stopwatch to time how long the mixtures have been left for and to time how long it takes for the mixture to drain.
- Distilled water to dilute the vegeren and to wash used apparatus with.
- Collecting beaker to collect the milk mixture after it has been drained.
- 100ml of Vegeren to coagulate the milk.
- 200 ml of Skimmed milk to test on.
- 200 ml of Semi-skimmed milk to test on.
- 200 ml of Whole milk to test on.
- Wax pencil to write on the apparatus to avoid confusion.
As I am testing the concentrations of vegeren and timings, the results to be obtained will provide quantitative data.
The independent variable (IV), which is the variable, I am able to control. In this case it is the amount of concentration of vegeren added to milk. This will cause an affect on the dependent variable (DV), which is the variable; I cannot control. I will be investigating this variable. In my experiment this is the time it takes for the milk to drain from the syringe.
Accuracy:
- Graduated apparatus will be used so quantities will be precise.
- After every result taken down, the apparatus, which has just been used, will be washed with distilled water so no vegeren or milk is left in the syringes and beakers etc.
- The amount of vegeren and milk used will be exactly the same in each case, as I will make sure that the meniscus is just touching the line.
Reliability:
- Each concentration of vegeren added to milk will be repeated three times and the average will be taken as the calculated result.
Pilot Tests:
Pilot test will be carried out to test how long I should leave the vegeren in the milk standing. This is necessary because I need a good amount of time to make sure it coagulates. If I released the milk mixture too early there could be little or no coagulation at all. If I released it too late, too much coagulation can occur and all the contents may not be able to be drained.
Another pilot test would be to test how much vegeren I need to add to the same amount of milk. This is important because a decent amount of vegeren is needed to coagulate the milk, too little vegeren may cause no coagulation and therefore results would be useless. Too much again would not only over -coagulate the milk, but also would waste a lot of the vegeren, which may be needed for the real experiment.
Method:
Pilot experiment:
A pilot test was conducted to investigate how long the mixture should be left for. The test was done on skimmed milk (randomly selected). 2 ml of vegeren was added to 2ml of milk and left for six minutes in a syringe facing down towards the lab table secured by a clamp and a stand. The plunger was then removed after the six minutes and was timed how long it took for the milk to come out. It was then repeated with twelve minutes standing time. The whole procedure was repeated once more but for a 50% diluted solution of vegeren. Another pilot test was done to see how much vegeren could be used. 2ml of vegeren was added to 2ml of milk. It was left for ten minutes and drained and timed. This was again repeated but for a 4ml vegeren solution with 2 ml of milk.
Actual experiment:
Firstly the apparatus was set up as shown in the diagram. Three separate beakers were filled with each milk, they were all in excess so if there were any faults, there was plenty of milk in the beaker. The entire contents of the vegeren bottle were emptied into a separate beaker. Another beaker was filled with distilled water, which was used to dilute the vegeren solution. Each beaker was labelled with a pencil, which was written straight on to the glass of the apparatus. This was done to avoid any confusion. A syringe was filled with whole milk till the 2ml mark and emptied into another beaker. The syringe was washed and used again to add 2ml of vegeren to the milk. At this point the stopwatch had just been started. With the same syringe, the mixture of vegeren and milk was gathered and the plunger of the syringe was pulled right to the end so it could easily be taken out after the time was up. The syringe was secured to the clamp and stand facing the table and left there for ten minutes. After ten minutes, the plunger was taken out of the syringe so it allows the contents of the syringe to drain out into a collecting beaker. As soon as the contents began to drain, another stopwatch was used to time how long it took for the solution to come out. The same procedure was repeated for the same milk and concentration of vegeren a further two more times for reliability. These were done simultaneously, but with approximately thirty-second gap between them so the coagulated milk can be released and timed with no interference of the other two experiments. After, the same procedure was repeated but for a different concentration of vegeren. This was achieved by placing 1.5 ml of vegeren in a beaker with 0.5ml of distilled water creating a 75% diluted solution adding up to 2ml. This solution was then added to 2ml of milk as before and timed for ten minutes just as before. It was also repeated three times. Then a 50% diluted solution was made with 1ml of vegeren and 1 ml of water and the same with a 25% diluted concentration giving four concentrations of vegeren altogether. The whole experiment was then repeated for the two other milks.
Results:
Pilot results:
This shows leaving the solution for 12 minutes will give a better reading. However it was decided that if the solution were left for 10 minutes, it would still give an accurate reading.
This shows that there wasn’t much difference between the increased concentration of vegeren and the standard 2 ml solution. In this case the 2ml solution will be used for the actual experiment so I can conserve the vegeren being used.
Actual Results (raw data):
Duration of the standing mixture: 10 minutes
Milk quantity: 2ml per each syringe
Whole milk
Semi-skimmed milk
Skimmed milk
Calculated results:
Whole milk
Semi-skimmed milk
Skimmed milk
Total average readings:
Analysis:
Within each milk, there has been an established pattern. Generally in all three milks, as the vegeren concentration increases in the milk, the longer it takes for the milk to actually drain out of the syringe. However the increase is very small. When each result was taken down for each concentration, some results were too low or too high but when the averages were taken for each milk kind, it was shown that there was still an increase. Also the averages were taken of all the concentration of vegeren results and it showed that as the concentration increased, the milk with the higher fat content took longer to drain as indicated on the graphs.
So generally there is an increase in time because of the increase in vegeren, which was expected, as there is more vegeren for the milk to coagulate. Also because of an increased in fat content of the milks, it also took longer to drain. This also was expected. So the results do support the hypothesis but only generally.
Although there was an increase in times, there was a fairly large gap between the drain timings of the whole milk and the other two milks. It was calculated at almost a second gap where as the other two milks, semi-skimmed and skimmed milk, have a very close gap between them, which was calculated to be within .10 differences. This was not expected and should not of happened in theory, instead the semi-skimmed milk should have been more or less half the whole milk, and the skimmed milk should been a tenth of that but only in theory. There was one anomalous result; this was the last result for the skimmed milk where it only showed an increase of .01 degree. These odd results could be because the syringes and other apparatus may have a not been cleaned as thoroughly as they could have leaving residue of milk and vegeren already in the syringe when used for the next experiment. Also it could be caused by inaccurate time taking, as it is difficult to release the plunger and start the stopwatch at exactly the same time as well as stopping the stopwatch.
The results have proved my hypothesis correct that the effect of the concentration of vegeren will affect three different milks. I conclude that as the concentration increases, the more the milk coagulates in the same amount of time. Also as the fat content increases in the milk, coagulation is much easier. This can be related back to the theory, which suggests that with more fat content, the more will be incorporated into the enzyme and so a thicker curd will form. As stated in the theory, enzyme conc. increases with successive collisions and was shown in this experiment. However it was not demonstrated that the enzyme was in excess.
Evaluation:
The experiment was generally conducted quite well, however there were obviously a few errors in the procedure.
There were a few limitations to experiment such as the difficulty of synchronised timings of the release of the plunger and the start of the timing. This may not have been a major problem if the quantities were more that way the time taken for the mixture to drain would be longer and a small error like this needn’t be taken in account. Another limitation was time, if there were more time available to complete the experiment with more readings then results could have been more accurate. Also the actual quantities available could be increased and can be seen as a limitation.
In order to improve the experiment; more quantities would be used; more time will be available; more readings would be taken to give a more accurate average; use of a new syringe for every mixture could ensure more accuracy.
In order to support my results, the same experiment could undergo but on a much bigger scale to improve accuracy and reliability.
Bibliography:
Internet – information on milk and milk content.
AS biology book – further information on enzymes.