What happens when Sudan III stain solution is added to a food sample containing lipids?

When Sudan III stain solution is added to a food sample containing lipids, the correct outcome is that it separates into two layers with a bright red top layer. This is due to the property of Sudan III, which is a dye that specifically stains lipids.

Lipids, which include fats and oils, are hydrophobic (water-repelling) substances. When Sudan III is introduced to a mixture containing lipids, it interacts with the lipid molecules and forms a complex that is colored red. Consequently, the lipids rise to the top of the solution because they are less dense than water, resulting in the formation of a distinct red top layer. This indicates the presence of fats in the sample.

Thus, the observation of a bright red top layer is a clear and visible indication of lipids present in the food sample, illustrates Sudan III's effectiveness as a lipid stain, and underscores the importance of this test in biological assessments of food content.