There are certain limitations for the disaccharides to give positive results. Benedict's reagent test can be used to test for the presence of glucose in urine, but this test is not recommended or used for the diagnosis of diabetes mellitus.
The principle of Benedict's test is that when reducing sugars are heated in the presence of an alkali they get converted to powerful reducing species known as enediols.
This colour is due to the presence of simple carbohydrates. Here sodium citrate is the complexing agent. Benedict's solution is a deep-blue alkaline solution used to test for the presence of the aldehyde functional group- CHO. Formation of red coloured copper I oxide indicates the formation of a precipitate. This precipitate is insoluble in water. Following this condition, high amount of brick-red colour precipitate will be formed at the end of the test tube.
Sometimes you will find small amounts of copper oxide along with brick-red precipitate. Another compound Sodium citrate complexes with the copper II ions to avoid degradation into copper I ions during storage. Some complex type of carbohydrates like starch or amylum consisting of a large number of glucose monomer units joined by glycosidic bonds. Sucrose which is commonly known as table sugar contains two reducing sugars moieties fructose and glucose.
These reducing sugar are joined by their glycosidic bond in such a way as to prevent the glucose isomerising 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 still indirectly can produce a positive result with Benedict's reagent if heated with dilute hydrochloric acid HCl prior to the test.
The acidic conditions and heat break the glycosidic bond in sucrose through hydrolysis process. 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.
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 myo-inositol is another carbohydrate which produces a negative test. Benedict's reagent can be used to test for the presence of glucose in urine.
Glucose found to be present in urine is an indication of diabetes mellitus. Once a reducing sugar is detected in urine, further tests have to be undergone in order to ascertain which sugar is present. Only glucose is indicative of diabetes. Benedict's quantitative reagent is used to determine how much reducing sugar is present. First, we had to adjust the pH of the solutions back to neutral before adding the Benedict's reagent.
We used a pH indicator and NaOH a base for this. We then added the Benedict's reagent. We got moderately positive results orangish color. This is because HCl breaks starch back down into its component monosaccharides glucose, in this case. Amylase is an enzyme that removes glucose molecules from starch. Both plants and animals use amylase when digesting starch.
Unfortunately, amylase cannot break the beta-bonds which hold the glucose molecules together in cellulose. If it could, we'd be able to eat hay. Based on this information, can you figure out what our results should be if we tested amylase-treated starch and amylase-treated cellulose solutions for reducing sugars?
Organic Molecules These are complex, carbon-containing molecules associated with living organisms. Most also contain hydrogen and oxygen. There are five major types: carbohydrates, lipids, proteins, nucleic acids, and vitamins. We covered the first three types in lab. A review of our carbohydrate test data is provided on this page. Click the molecule types above to link to the associated review material. Interpreting Benedict's Reagent Results Benedict's reagent starts out aqua-blue.
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