Although we consider it non-fat, skim milk actually has very low levels of lipids. therefore, it should test positive with sudan solution. why is the sudan test for skim milk negative?

Ans.

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.

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.