Protein assays is the method to determine the amount of protein in an unknown solution. They do this by measuring certain distinctive protein characteristics which involve UV absorbance. Proteins are polymers of amino acids, where amino acid units are joined by peptide bonds which have partial double bond character and absorb light. Proteins also may contain some amino acids with aromatic rings in the side chains. These distinctive features are the most relevant in the measurement of absorbency. The usual techniques for determining protein concentration depend on using a standard protein to calibrate measurements for accuracy. All protein assay techniques are prone to inaccuracy due to a variety of variables that may affect absorbency. There are 2 techniques for protein assays which is Biuret assay, determining protein concentration at absorbance 540nm and 750nm for the Lowry assay by using spectrophotometer.
In this experiment, we use Lowry assay technique to determine the concentration of protein in gelatin solution. The result is shown in the table below:
Then, we use this Lowry method to test the concentration of protein in grade A, B, C egg and duck egg as our sample. The result is shown in the table below:
From the graph, we got the non linear curve. It is because these methods rely on the presence of readily oxidizable amino acids such as tyrosine, cysteine, and tryptophan there is a variation in response from proteins with differing amino acid content. Therefore it is advisable that the protein used for generating the standard curve be consistent from experiment to experiment. Likewise, an overabundance of the amino acids in relation to the assay reagents, as would occur with high protein level, will result in a loss of linearity of the assay. Besides that, the presences of bubble in cuvette also affect the result of the experiment. Then, avoid touch the cuvette using hand because it will affect the reading recorded by spectrophotometer. Actually, when the graph is plotted, it forms the standard linear curve because when the concentration of protein in gelatin is high, the absorbance recorded on spectrophotometer also high.
From the table above, we got the high concentration of protein in grade B egg (sample B) which is 29.61mg/L while the lower concentration of protein in grade C egg (sample C) which is 21.26mg/L. Second one higher is duck egg (sample X) which is 27.30 mg/L and grade A egg has 23.33 mg/L. That means the protein content in grade B egg is higher than in grade A, C and duck egg. As we known, the price for the duck egg is more expensive than the grade A, B and C egg. So, as a good consumer, we should choose the grade B egg because from our research in laboratory, grade B egg has high protein content compare with the grade A and duck egg. Although, the size of the grade A egg is large compare with grade B egg but it not determine that it has high protein content. So, from now on, if you want to buy the grade A egg, you have to think about its protein concentration and that eggs must be more expensive than grade eggs.
As a conclusion, I can say that the grade of an egg is not enough to determine the protein content in it. As a wise consumer we should choose to buy grade B egg because it has more protein content, more valuable and the prize is cheaper than the grade A egg and duck egg.
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