<P> The color of the obtained precipitate gives an idea about the quantity of sugar present in the solution, hence the test is semi-quantitative . A greenish precipitate indicates about 0.5 g% concentration; yellow precipitate indicates 1 g% concentration; orange indicates 1.5 g% and red indicates 2 g% or higher concentration . </P> <P> To test for the presence of monosaccharides and reducing disaccharide sugars in food, the food sample is dissolved in water, and a small amount of Benedict's reagent is added . During a water bath, which is usually 4--10 minutes, the solution should progress in the colors of blue (with no reducing sugar present), green, yellow, orange, red, and then brick red precipitate or brown (with high reducing sugar present). A color change would signify the presence of a reducing sugar . The common disaccharides lactose and maltose are directly detected by Benedict's reagent because each contains a glucose with a free reducing aldehyde moiety, after isomerization . </P> <P> Sucrose (table sugar) contains two sugars (fructose and glucose) joined by their glycosidic bond in such a way as to prevent the glucose isomerizing to aldehyde, or the fructose to alpha - hydroxy - ketone form . Sucrose is thus a non-reducing sugar which does not react with Benedict's reagent . Sucrose indirectly produces a positive result with Benedict's reagent if heated with dilute hydrochloric acid prior to the test, although after this treatment it is no longer sucrose . The acidic conditions and heat break the glycosidic bond in sucrose through hydrolysis . The products of sucrose decomposition are glucose and fructose, both of which can be detected by Benedict's reagent, as described above . </P> <P> Starches do not react or react very poorly with Benedict's reagent, due to the relatively small number of reducing sugar moieties, which occur only at the ends of carbohydrate chains . Inositol (myoinositol) is another carbohydrate which produces a negative test . </P>

Would ribose react with benedict's reagent as glucose does