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Introduction

Name: Nguyen Hong Hanh Class: 5X 1. Aim To investigate the amount of protein present in different types of milk by measuring the mass of protein in each types of milk. 2. Introduction Casein is a protein which is found in milk. This is a conjugated protein that has prosthetic groups that is called phosphoric acid, covalently bonded to the R-groups of some amino acid residues. Thus casein is also called phosphoprotein. Casein is insoluble in water. The addition of dilute acid to milk - the precipitate is known as acid casein. In order to estimate the amount of protein present in each type of milk, we can measure the mass of its coagulation in acid. Hypothesis -The mass of protein in full cream milk is highest while the mass of protein in soya milk is lowest. Independent variable Four different types of milk, namely full cream milk, skimmed milk, goat's milk and soya milk. Dependent variable Amount of protein present in each type of milk, measured in terms of average mass of protein. Controlled variable Variable How it is controlled Volume of HCl used 10ml of each dilute HCl is used for the first three types of milk Volume of milk used 20ml of each types of milk is used Duration in which the milk is settled and let the casein precipitate out of the milk All types of milk are settled for 5 minutes Duration for ...read more.

Middle

Graph: 7. 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. ...read more.

Conclusion

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. 8. 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. 9. Evaluation Limitation/weakness Evaluation of limitation/weakness Suggestion for improvement Instrument used in measuring the mass of casein Limited precise of balance (only 0.1g). Smaller change in the mass cannot find out Use a balance that has a greater precise - up to 0.001g Short of duration to allow the precipitate out of the milk (5 minutes) 5 minutes may not be long enough for precipitate out of the milk. Increase the duration for allowing the precipitate out of each type of milk to 15 to 25 minutes Using different types of filter (cheese cloth and filter paper) Using different filter, causing the significant change between the mass of protein present in 4 types of milk Using one type of filter (cheese cloth or filter paper) Data comes from different results Some of readings minus the cheese cloth or filter paper, or some of readings did not Must use the identical result, ex: all the data minus the cheese cloth or all the data did not minus. 10. ...read more.

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