Proteins are polymers of amino acids that are joined by peptides bond. The reaction that is used to measure protein concentrations, is called the Biuret Protein Assay. The peptide bonds in protein are bound by Cu(II) cations in a basic solution in the Biuret assay. The absorbance of light at 540 nm, A540, is determined by the blue colour through spectrophotometer. A standard curve is plotted that the relationship is the absorbance of light at 540 nm versus the different concentration of gelatin. A straight light will be formed and an equation that fit the straight line is determined. Through this graph one can find the unknown protein concentration, for example to determine the protein concentration of different grade eggs.
Graph 1: The absorbance of light at 540nm versus the different gelatin concentration.
Through the observation, we obtain the protein concentration of grade A egg is 14.23mg/L while duck egg is 18.67mg/L. From this statement, many people will prefer to buy the duck egg. But, the percentage difference between the protein of grade A egg and duck egg is 23.8%. A grade A egg costs RM0.34 compare with the cost of a duck egg, which is RM1.00. It is more worth to buy a grade A egg compare with duck egg because we can get higher amount of protein by spending the same amount of money.
From the experiment results, the concentration of grade B is higher among the 3 grade eggs, which is 16.38%. The percentage difference between the protein of grade B egg and duck egg is 12.3%. The cost of a grade B egg is RM0.32 while it is RM1.00 for a duck egg. The price of a duck egg is three times higher than the price of a grade B egg. Therefore, consumers are advised to buy the grade B eggs to save money. Imagine that you can spend RM1.00 to buy 3 grade B eggs that have protein concentration equal to 49.14mg/L. Or you are willing to buy a duck egg which cost RM1.00?! Think carefully!
The percentage difference between the protein of grade A egg and grade C is 30.0%. The concentration of protein grade C is 10.95mg/L, which is the lowest protein concentration among these three grade eggs. So the cost of grade C eggs is RM0.30. The difference between them is only about RM0.02. So consumers are advised to buy grade A eggs that contain more protein compare to grade C eggs.
The percentage difference between the protein of grade A egg and grade B is 13.1%. The protein concentration of grade B egg is higher than grade A egg, which are 16.38mg/L and 14.23mg/L. The cost is RM0.34 and RM0.32. From here, actually many people will think that the protein content in grade A egg must be higher than grade B egg. But through the experiment that we done in laboratory, we can make an assumption that the protein content in grade B is higher than grade A. By using mathematical knowledge to count; we can save RM0.60 when we buy a set of grade A egg and get more protein. Do you agree?
In a nutshell, the grade of an egg is not enough to determine the protein content. From the experiment, we advice consumers to buy grade B egg that contain higher protein content and with lower price. We hope everyone can become a wise consumer.
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