Protein Concentration Lab Report
Determining Protein Concentration
Of Dean’s 2% Milk compared to a Protein
Powder
Nutritional Supplement
By: Mike Hoover 638853
Biology 111 Lab, Wed@12p.m.
February 13, 2012
Lab Partners:
Sam Klingenberger
JayDee Schmucker
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Protein Concentration Lab Report
Abstract
To determine the protein content of unknown samples, we use the
Quick Bradford assay. A dye was mixed with samples and the
absorbance was measured with a spectrophotometer. Once the
absorbance is measured, we compared them to a standard curve line to
make the information comparable and measureable.
The samples used in our experiment were 2% milk (Dean’s) and a
protein powder nutritional supplement. We diluted our samples and
added Coomassie Blue G-250 dye. The dye binds to the proteins and
makes it easier to measure. The samples were taken to a Bio-Rad
SmartSpec spectrophotometer and the absorbance was measured
along with a standard solution made from Bovine gamma globulin.
After all measurements were taken, we organized the data to
determine that the hypothesis was supported and the protein powder
did actually have higher protein content.
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Protein Concentration Lab Report
Introduction
Many people know of the nutritional advantages of a diet rich in
protein. But how do you know how much protein is in the food you
eat? Are the labels on the food accurate? How do the labels get the
numbers they show? How can you determine the amount of protein in
any given specimen?
To determine the protein content in a lab, we use the Quick Bradford
assay. This is done by diluting a protein sample, adding dye and
measuring absorbance using a spectrophotometer. This gives us a
concise view of the protein content in a given specimen.
In our experiment, we measured the protein content of two different
samples- 2% milk and a protein powder nutritional supplement. We
measured the absorbance of our samples and of a standard made from
a dilution of Bovine gamma globulin. After all measurements, we
developed a standard curve graph to compare amounts of protein in
each sample.
It was found that the protein powder sample had more protein
concentration than the milk, which was previously hypothesized.
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Protein Concentration Lab Report
Materials and Methods
Our protein powder sample was prepared by mixing one scoop of
the powder with 8oz of water. Then, 4ul of the protein powder sample
and 4ul of the milk sample were each diluted with 196ul of PBS
(phosphate buffered saline).
After diluting our samples, 20ul of each sample was placed in their
own respective cuvette. Then, 1ml of the Coomassie Blue G-250 dye
was added and mixed in the vortex. After mixing, the samples were left
to incubate at room temperature for 5 minutes (or no longer than one
hour). Once the samples were done incubating, they were taken to the
Bio-Rad SmartSpec Plus spectrophotometer to measure the
absorbance.
Cuvettes labeled 1 through 7 were a standard made from a serial
dilution of Bovine gamma globulin with a concentration of 0.125, 0.250,
0.500, 0.750, 1.000, 1.500, 2.000mg/ml respectively, and were mixed
with the Coomassie Blue G-250 dye. Our samples were visually
compared to the standard samples and then the absorbance of each
standard was measured using the Bio-Rad SmartSpec Plus
spectrophotometer and then our two samples.
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Protein Concentration Lab Report
Results
As the concentration increased, the absorbance did also. Our samples
are shown in the figure below as the black points on the line graph.
(Figure 1) The green is the Bovine gamma globulin standard. The 2%
milk had an absorbance of .109 and the protein powder sample had an
absorbance of .438.
(Figure 1)
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Protein Concentration Lab Report
Discussion
These findings support my hypothesis that commercially-manufactured
protein powder has a higher concentration of protein than does 2%
milk.
Before testing the absorbance of the samples, we visually evaluated the
protein content by determining which had a darker blue color from the
Coomassie Blue G-250 dye that binds to the protein. The protein
powder did have a darker blue color and thus, did have the actual
higher protein content.
In the future, I would like to test the protein content of different brands
of protein powder to compare with their own labels and determine
which is the highest per serving size.
References
Knisley, Karin.2009 A Student Handbook For Writing In Biology.
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