Sudan reagent is used for identification of fats and lipids in the food, feacal and other biological fluids. It gives red color in the presence of lipids and fats. The amount of lipid in the skimmed milk is negliable or very low. Therefore, the Sudan test is negative in skimmed milk.
Sudan test is a method to detect presence of lipoproteins, lipids, and triglycerides in samples. The presence of lipids is detectable by change in color of Sudan dye.
Non-fat or skim milk contains a small of amount of lipids, so the result should be positive when Sudan test is performed with skim milk.
Although, skim milk contains very little concentration of lipids, due to which the change is color during test is undetectable. Thus, skim milk gives negative results with Sudan test.
The Hershey–Chase experiment was based on a bacteriophage T2 (a virus), to that DNA is the genetic material. Bacteriophage T2 attacks bacterium and makes its copies. Based on the experiment, Hershey and Chase deduced that it is the DNA of virus enters bacteria to make virus copies. To trace viral DNA, Hershey and Chase label DNA with ³²P (radioisotope of phosphorus) because phosphorus is not present in most of the proteins.
