Bio Nerds: Milk Lab

Purpose

In this lab, we were trying to determine the actual percentage of protein on skim milk. We were testing protein properties (such as protein denaturation). In this scenario, the dependent variable would be the molecular structure and the the independent variable would be the acetic acid added to the milk.

Introduction

Proteins are macro-molecules composed of chains of amino acids. The sequences of amino acids usually result in the different structures (primary, secondary, tertiary and quaternary) which then determines it's function. When a chain of amino acids come together, they form polypeptide bonds.

Methods

In this lab, we started off by weighing an empty beaker so we could later subtract this mass from the mass of the liquid and the beaker combined. We then measured out 15-mL of non-fat milk into the beaker. Next we added acetic acid to the beaker filled with milk and stirred it. We then recorded the mass do the solution and the beaker together. Next we poured the solution through a filter paper and into a beaker. The filter paper caught the curds. We then let the filter paper and curds dry out over night and massed it the next day.

Data

Discussion

The overall objective of the experiment was to determine the percentage of protein that is in nonfat milk, according to the label there is supposedly 8 grams of protein per serving. We calculated a -31.152% error meaning that we had approximately 30% less protein found in our milk then our expected value. The reasons behind this error could be as follows: incorrect measurements and the filter paper used to filter out the protein. In order to revise and improve the experiment for another test, there must be a more efficient way for filtering the milk solution and separating out the proteins. More precise measurements and calculations would help to determine a more accurate account for the protein.

The results of the experiment support our hypothesis on the outcome of the experiment because protein was shown to be present when the milk and its proteins were in the process of separating. When Biuret reagent was added, the remaining coagulated milk turns a purple color meaning that protein leaked through the funnel into the liquid and separated from the rest of the protein.

(Amount of Protein Per Serving: 8g)

Sample from Non-fat milk

Adding concentrated acetic acid to milk

Acid denatures milk protein

Milk begins to form curds

Solution poured into funnel to separate protein

Using water as negative control.

Adding Biuret to milk solution.

Purple color shows presence of protein in solution.

Separating protein from funnel.

Setting filter paper to dry overnight.

Conclusion

To conclude our experiment, the actual percentage of protein found in skim milk (due to our findings) was much less than what we expected it to be. The carton said there was supposedly 8 grams. We found a lot less than this. We are basing our information off of the data we found in this lab. There might have been skewed data from incorrect measurements at times but generally our findings were accurate.