D20071029499: Does the grade of an egg determines the protein content?

Proteins are polymers of amino acids that are joined by peptide bonds. Biuret assay is used to measure the concentration of protein in the solution. The concentration of protein is measured by absorbance of light at 540 nm, A540, using a spectrophotometer. In Biuret assay, Cu (II) ion will bond to the peptide bonds in protein in a basic solution. At the end of experiment, a standard curve is plot between the absorbance of light at 540 nm and the concentration of protein in the assay. From the graph, the unknown concentration of protein will be determined.

Graph 1: The absorbance of light at 540nm versus the different gelatin concentration.

From the table above, the concentration of protein in duck egg (sample X) is 18.67mg/L, while the protein concentration of grade B’s (sample B) egg is 16.38mg/L. Thus, difference of percentage between the duck egg and grade B egg is just 12.3%. This means that the concentration of protein between these two eggs is slightly difference. The price for one duck egg is almost RM1.00, while the price for a grade B egg is RM0.32. This means that we have to spend three times the money to buy a duck egg although the difference of protein concentration is not much. Besides, the protein concentration of grade A egg is 14.23mg/L, thus the difference percentage of concentration of protein between the duck egg and grade A’s (sample A) egg is 23.8%. So, what do you think? Grade A or duck egg? We can buy three eggs instead of one duck egg by just spending RM1.00. Thus, the concentration of protein of three eggs is more than concentration protein of one duck egg.

But when we compare the concentration of protein between the grade A, B, and C egg, the concentration protein of grade C egg is 10.5mg/L, thus the percentage difference between grade A and C is 30%. From the result, we have to buy the grade A egg, although the price for the grade A is RM0.34 and grade C is RM0.30. The reason is when we spend more RM0.04; we can get more 30% the protein. But, for the grade A and grade B egg, the percentage difference is just 13.1%. From the result we obtain, we no need spend more RM0.02 to buy the grade A egg. This is because when we buy the thirty eggs of grade B in once, we can save RM0.60 and buy two more grade B eggs. Thus, as a wise consumer, are you agree with me?

As a conclusion, the grade of the egg does not determines the protein content. Thus, it is worth to buy the grade B egg that contains the more protein content.