Purpose: in this experiment we look at denaturing proteins. We are using denaturing to figure the amount of protein that is found in milk. We are testing the amount of denatured protein that we find in the milk compared to the amount of milk tested.
Introduction: proteins, also called polypeptides, are made out of chains of amino acids. The amino acids contains: a central carbon (C), carboxyl group (COOH), amino group (NH2), and a side chain (R). The amino acids are formed together using a process called dehydration synthesis. When this occurs one H from the amino group bonds with the OH from the carboxyl the result is a two bonded amino acids and a molecule of water. The bond that is formed is called a peptide bond. In this lab we use denaturing to break the peptide bonds of proteins. Denaturing is a disruption of the peptide bonds caused by thing like heat, salt concentration, pH and other environmental factors.
Methods: the first thing we did was weigh the milk to establish the net mass of the milk. After this we added acetic acid to the milk, briefly stirred, and let the acid denature the proteins. After this stage we separated out the whey protein from the casein protein by filtering the milk, denatured proteins could slip through the filter while the curds stayed in the filter. The filteration was complete we re weighed the dry protein captured by the paper filter and noted our measurements.
Data: We found there was .66g of dry protein in the milk out of a total of .51g of protein in milk. We had a percent error of 29.41% and a percent yield of 129.41%
Graphs and Charts: (insert graph here)(insert photos here)
Discussion: denatured protein comes in curds and is used in foods such as cottage cheese and yogurt. Denaturing occurs when proteins are affected by pH temperature or other environmental factors. When proteins are denatured they turn into singular strands of amino acids. These strands clump together to form curds. We tested the weight of the left over curds that was left in the filter paper. In the end of the we found there to be .66g of protein. The expected value of protein for a 15 mL is .51g. We ended with a percent error of 29.41%. Somehow we ended up with more protein than the expected value. This percent error could be considered to be higher because when the liquid was tested with the Buriet solution we found that protein remnants were not denatured and was filtered through. We also had trouble with the filter paper when it became stuck onto our 50 mL glass. We got majority of the paper off and weighed, but there were fragments left behind. Many things could be accounted for the excess weight. One theory is that when the filter paper was left out residue collected onto the filter paper adding extra weight. Another theory can be attributed to absorption. When we observed the filter paper the next day we found there to be water marks left on the filter paper. When the substance was being filtered the liquid was absorbed by the filter paper adding extra weight to the denatured protein. If we were to redo the experiment with ideal conditions we would use a filtering system that does not absorb the fluid. We also would have a added more acetic acid so that more protein would be denatured and not left over in the filtered solution.
Conclusion: In this experiment we denatured protein through the use of acetic acid. We didn't let the milk sit long enough with the acetic acid to denature, but we still had favorable results. The milk denatured to seperate into casein and whey protein.
References: Charles Filipek, http://healthyeating.sfgate.com/much-protein-milk-have-5319.html
