The Seliwanoff test does not detect fructose in sucrose directly, but it helps to distinguish sucrose from fructose. Sucrose is a disaccharide composed of glucose and fructose, but in its intact form, sucrose does not show the same reactivity as free fructose. When sucrose is hydrolyzed (broken down into glucose and fructose), fructose will react positively in the test, showing the typical red color.
