Purpose
The purpose of the experiment is to use the process of denaturing to find the amount of protein in the non-fat milk that was provided. We are comparing the amount of denatured protein that we find to the amount of milk tested in the experiment.
Introduction
Method
In this experiment, we are trying to find the amount of protein in the milk. Proteins are made up of links of amino acid which can be broken down into even smaller groups; Carboxyl group, amino group, a central carbon, and a side chain. When dehydration synthesis occurs, or the joining of amino acids, it results in two joined amino acids and an H20 molecule. This happens when an H from one group bonds to an OH. This is called a polypeptide bond, or a protein bond. In the experiment, denaturing breaks these bonds and allows us to see how much protein is in the milk.
First we massed an empty 50 mL beaker, and then added 15 mL of non-fat milk to the beaker and re-massed it in order to calculate the mass of the milk.
milk protein, forming curds.
After that we weighed the filter paper and recorded it’s mass. We put a funnel on a ring stand above a clean 150 mL beaker, and folded the filter paper and put it in the funnel. We then poured the coagulated milk into the funnel and rinsed out any remaining milk curds in the 50 mL beaker. We removed the filter paper and placed it in a massed styrofoam cup with some paper towel packed into the bottom to absorb any remaining filtrate, and we let it dry overnight.
We labeled two test tubes, 1 and 2 and added 1 mL of distilled water to test tube 1, and 1 mL of milk filtrate to test tube 2. The water tube served as our negative control. We then added 1 mL of Biuret reagent to each test tube, and the solution was a bit purplish blue color so protein was present.
Data
Graph
Discussion
Percent difference is the percentage of relative change calculated from the change between the experimental (measured) and theoretical (accepted) values divided by the theoretical value. Relative to this lab, the percent difference was defined by the amount of protein we found in 1mL of milk (.37 g) minus the amount of protein we should have found in 1mL of milk (.51 g) all divided by the amount of protein we should have found in the milk (.51 g) which equals -.27. In order to find out the percent difference we multiplied that number by 100, giving our experiment a -27% error. Compared to the data we should of recorded, our numbers varied by -.27%. The lack of collected protein in our milk sample could have been caused by several variables. However, the most realistic option suggests that the deficiency of protein was due to whey. Whey is the watery substance left over after milk curdles. We assumed that whey wouldn't contain any protein because all the protein was supposed to have curdled. But to our surprise after testing the whey with the Biuret solution (strong base), it turned slightly blue which means it detected the presence of proteins. After further research, we found that whey is actually a protein and contains both alpha helix and beta pleated sheet structures. Because whey protein contains both structures it is a rich source of amino acids, which could mean that a higher pH is needed to denature all of the proteins. Looking at the results, acetic acid must have not been acidic enough to denature all of the whey protein. Whey protein is also common among athletes as they hope to increase muscle mass and improve performance. Because of the strong abundance of amino acids in whey, it is said that they are readily absorbed by muscles post workout, which will help with recovery ("Vitamins & Supplements"). If we were to do this again to obtain more accurate results, we could add a larger amount of acetic acid into the milk sample or we could find a more acidic solution.
Conclusion
In the end, our results show that we got about 73% of all the protein from our milk sample which in the regular world is a passing score, however it is a barely passing score. But because we did not have a specific question or hypothesis to answer the results are very successful for a reaction that was not very professionally executed. The results could have been improved if more variables had been controlled such as more powerful acetic acid, temperature and human errors.
References
"Vitamins & Supplements: Whey Protein." WebMD. WebMD, n.d. Web. 22 Sept. 2014.