Materials
20ml dilute HCl
40ml full cream milk
40ml skimmed milk
40ml goat’s milk
40ml soya milk
2g MgSO4
4 filter paper
4 cheese cloth
Distill water
- Procedure
Refer to worksheet titled ‘determining protein content in milk
- Results:
Calculation:
- Start by keying in the data into a column
Ex: skimmed milk: B5 to H5
- The mean is calculated with the AVERAGE function
Ex: Calculate the mean of the values in skimmed milk B5 to H5
fx = AVERAGE (B5:H5)
- For standard deviation use the STDEVA function
Ex: Calculate the standard deviation of the values in skimmed milk B5 to H5
fx = STDEVA (B5:H5)
Calculation:
-Mass of protein per 20ml of skimmed milk = (20 x 3.4)/100 = 0.68g
- Graph:
- Discussion of results
Anomalous results
There were 2 anomalous readings in the data collected. There were in reading 2 of full cream milk and in reading 4 of soya milk. They were highlighted in table 1. It is because the precipitates are not enough time to settle; thus the precipitates are not completed out of the milk. The liquid is not removed as much as possible or squeezing the solid too much out of the cheese cloth. This makes the mass of protein inaccurate in reading 2 because of the amount of liquid. Or the precipitates are not filtered enough; still remain the liquid on the filter paper. The mass of protein in reading 4 is anomaly. Therefore, their values differ greatly from those of other readings. As a result, they have been excluded when calculating the average mass of protein and standard deviation.
Results of investigation
According to my result in table 3, the mass of protein in full cream milk is highest while the mass of protein in goat milk is lowest. However, according to the value of nutrition panels in 20ml, the mass of protein in full cream milk is highest (0.68g) while the mass of protein in soya milk is lowest (0.24g).
Compare to my result, the protein yield in nutrition panel differ the protein yields in my experiment. For the protein yield in nutrition panels, the mass of protein in goat milk is greater than the mass of protein in soya milk whereas the mass of protein in goat milk is smaller than the mass of protein in soya milk in my result. Almost milk contain casein, but the soya milk is a special kind of milk. This is formed from soy bean. Almost protein present in soy milk is soy protein, thus the soya milk contain very little casein or has lack of casein. Leading the procedure determine the protein in soya milk differ that of remaining milk. That’s why the protein present in soya milk is lowest in four types of milk.
The mass of protein present in soya milk is greater than that of goat milk in my experiment. It is because the precipitates are not enough time out of the milk. When adding the solution that contains goat’s milk through the cheese cloth. It is filtered very quickly, leading the precipitates did not present in cheese cloth. The soya milk is filtered by filter paper and is left in one day, however, some filter papers contain precipitate and little amount of liquid. This makes the result inaccurate and lead the amount of protein present in soya milk is greater than the amount of protein present in goat’s milk. Furthermore, the raw data is not collected equally. It is because some data minus the cheese cloth or filter paper, or some data did not.
Casein exists as calcium salt, calcium caseinate. The isoelectric point of calcium caseinate is a pH 4.6.It is insoluble in solution that has pH less than 4.6. The pH of milk is 6.6; therefore, casein has a negative charge at this pH and is solubilized as a salt. If it has an addition of acid in milk, the negative charges of casein are neutralized or increased, the solubility of casein decrease, thus the protein precipitates and calcium ions present. For soya milk, it contains very little casein or lack of casein, main protein is soy protein. It cannot be determined by adding dilute HCl. Because casein is a group of soluble protein, heating soya milk, the protein will be denatured, loses their three dimensional shape. Protein’s solubility decreases in milk and precipitates present in the solution. Additionally, it is left in one day, it allows the milk to sour, thus the lactic acid produced precipitates the casein.
- Conclusion
-The mass of protein in full cream milk is highest while the mass of protein in soya milk is lowest. This agrees with the hypothesis proposed for the investigation. However, my results do not support the hypothesis because of some limitation or weakness.
- Evaluation
- References:
-Option C. Cells and energy – C.1 Proteins
-Internal Assessment – Core 1.1 Statistical Analysis
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