To Perform Qualitative Test for Reducing Substances in Urine
Sugars may be called as reducing or nonreducing based on their ability to reduce copper during the Benedict’s test. The reducing property of sugar is based on the presence of free aldehyde or ketone group in them. Most of monosaccharides and disaccharides are reducing sugars, while sucrose is nonreducing sugar. Reducing sugars are capable of reducing Cu2+ (cupric ions) to Cu+ (cuprous ions) in alkaline medium which produces red precipitate of cuprous oxide or yellow precipitate of cuprous hydroxide. The urine of normal individuals contains small amount of reducing substances which are not sufficient to give positive test with Benedict’s test or Fehling’s test. Various reducing sugars present in the urine are glucose, galactose, fructose, and lactose.