Workshop: Got Protein? By Ricardo Chiesa The purpose of this workshop was to test the protein content of different types ofmilk, using the Bradford Protein Assay. This method uses Coomassie blue dye, whichbinds to the side chains of specific amino acids. In this experiment, the protein that wasquantified was casein, the most abundant protein in milk. This blue staining can bind to 13different amino acids of the 224 amino acids casein has. First of all, I diluted two samplescontaining different types of milk with phosphate buffered saline (PBS 1x), and then it wasdiluted again with the protein dye reagent. Afterwards, 7 sample standards with differentknown concentrations of casein were prepared, adding the protein dye reagent to each ofthe standards. The purpose of this step was to visually compare the test samples (milks)with the known concentration samples, and to decide what the unknown concentrations ofthe milks were. Later, I proceeded with the analysis of all the samples using aspectrophotometer to measure the absorbance, which was going to be proportional to theprotein concentration. Once this information was obtained, I prepared a standard curve withthe values and, finally, the exact concentration of protein in the test samples was calculatedin mg/mL.