Does the grade of egg determine the protein content in it?
In this lab experiment, we do protein assays by using Lowry assay method to determine the protein concentration. The concentration of protein is measured by the wavelength of 750nm, A750, by using spectrophotometer. At first, we mix 0.1 mg/L of 0.25 ml of gelatin (protein) with 2.5 ml of Lowry reagent 1 into the cuvette. After 10 minutes, we add 0.25 ml of Lowry reagent 2 into the cuvette and immediately mix well. Then, we repeat the first and second step by replacing 0.1 mg/L of 0.25 ml of gelatin by 0.2 mg/L, 0.3mg/L, 0.4mg/L, 0.5mg/L and 0.6mg/L of 0.25 ml of gelatin into other prepared cuvettes. After 30 minutes, we put each cuvette with different protein concentration into the spectrophotometer and the results are recorded in the table below. 
In addition the method is sensitive; samples containing as little as 5 µg of protein can be analyzed readily. The color formed by the Lowry reagent is thought to be caused by the reaction of protein with the alkaline copper in the reagent and the reduction of the Cu2+ (cupric) ions in the reagent to Cu1+ (cuprous) by the tyrosine and tryptophan residues of proteins. The cuprous ion in turn reduce the phosphomolybdate-phosphotungstate salts in the reagent to form an intensively blue complex. Because the content of these two amino acids varies substantially within proteins, the color yield permiligram of protein is not constant. It may differ substantially from that of a protein standard. Nevertheless, the method is very useful for following changes in protein content, as, for example, during purification of a protein.
The ability to easily and reliably quantitate total protein content in samples is paramount to many biological assays. Although the Lowry protein assay was first published in 1951, several improvements, not the least of which is the reduction in assay volume, have increased sensitivity of the assay. Recently fluorescent protein assays have been developed with improved sensitivity (3), but the cost per assay can make them unacceptable for large numbers of samples.
Although the Lowry total protein assay has withstood the test of time, there are several features of the assay that have to be kept in mind. 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. In extreme cases this will lead to a precipitation of the chromogens and loss of color prematurely. Likewise, the assay color is only stable for approximately one hour, after which a similar phenomenon occurs in samples with normal concentrations.
From the experiment result, concentration of protein in X (duck egg) has more protein content compare to grade A, B and C egg. Although duck egg has more protein content and is good for our health but if we compare the cost we found that a duck egg is more expensive than a grade A, B and C egg. From the result, we have to buy the grade A egg because it has more protein content than grade B and C egg.
While in Omega-3, they are essential to human health but cannot be manufactured by the body. Omega-3 fatty acids can be found in fish, such as salmon, tuna, and halibut, other marine life such as algae and krill, certain plants (including purslane), and nut oils. Also known as polyunsaturated fatty acids (PUFAs), omega-3 fatty acids play a crucial role in brain function as well as normal growth and development. It contributes to the development of disease while a proper balance helps maintain and even improve health
As a conclusion, the grade of the egg does not determine the protein content.
prepared by d029491
