In 2008, a major case of melamine and cyanuric acid poisoning was caused by Chin

Question

In 2008, a major case of melamine and cyanuric acid poisoning was caused by Chinese manufactured infant formulas resulting in the hospitalization of over 50,000 children with kidney stones. At least 6 deaths occurred. The food industry commonly determines protein concentration using an acid hydrolysis assay that measures nitrogen content. Melamine and cyanuric acid are inexpensive and are rich in nitrogen. To find an alternative protein assay suitable for food products, the Bradford experiments below were performed. (adapted from Field and Field, Food Chemistry. 2010. 121(3):912-9J7) QUESTIONS: Looking at Figure A, purified BSA (bovine serum albumin) and reconstituted-powdered milk at various protein concentrations were measured using Bradford assay. A significant difference is observ ed between the BSA and the milk curves. For example, at 10 mug/ml, BSA had an A595 of about 0.6, whereas milk had an A595 only about 0.3. Provide an explanation on why milk and BSA have very different A595 readings when tesed at the same concentration. Looking at Figure B, various combinations of milk, melamine, and cyanuric acid were tested using a Bradford assay. Comparing assays 5 thru 7, what can you conclude about the detection of melamine or cyanuric acid by Bradford assay? Using a Bradford assay, melamine does not significantly interfere with the detection of protein in milk samples. Comparison of which two assays supports this conclusion? Considering the standard acid hydrolysis assay used by the food industry, explain why the Bradford assay is the assay of choice when testing milk samples potentially adulterated with melamine and/or cyanuric acid.

Explanation / Answer

BSA contains more protein compared to milk. Increased concentration of protein shows increased absorbance.

From the assays 5 thru 7, we can conclude that Bradford assay is not suitable for finding non protein compounds like melamine or cyanuric acid.

Comparison of assays 1 and 2 supports this conclusion.

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