Verified answer

Examples of disaccharides are maltose, sucrose, and lactose.

Benedict’s solution test is a general food carbohydrate test used to differentiate reducing sugars (maltose & lactose) from non-reducing sugar (sucrose) among disaccharides. But it cannot identify which one is maltose or lactose among reducing sugars.

Besides distinguishing between reducing sugars and non-reducing sugar, Benedict’s solution test is semi-quantitative which means that it can be used to give a rough estimate of the amount of reducing sugars present. The change in colour from green, yellow, orange to red-brown and the amount of precipitate indicates the increasing concentration of reducing sugars.

To perform Benedict’s test, you add 2 ml of a solution of sugar to a test tube. Then, add an equal volume of Benedict’s solution. Shake and bring gently to the boil, shaking continuously to minimize spitting. The Benedict’s solution contains copper sulphate which gives the solution its blue colouration. If reducing sugars are present, they will reduce copper sulphate containing copper (II) ions to insoluble copper oxide containing copper (I) ions. Thus, the blue colouration of mixture turns green, yellow, orange, and then forms a brick-red precipitate. On the other hand, the mixture will remain blue colouration if reducing sugars are not present.

The Lugol iodine solution cannot detect the presence or even identify the disaccharides; it is used for detection of presence of starch (polysaccharides). To test presence of starch, you add a few drops Lugol iodine solution to 2ml 1% starch solution (or to the cut surface of a potato), a blue-black colouration will be observed indicates the presence of starch ( iodine forms a polyiodide complex with starch).

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RESULTS

CONCLUSION

ANALYSIS

The Benedict’s solution contains copper sulphate which gives the solution its blue colouration. If reducing sugars are present, they will reduce copper sulphate containing copper (II) ions to insoluble copper oxide containing copper (I) ions. Thus, the blue colouration of mixture turns green, yellow, orange, and then forms a brick-red precipitate. On the other hand, the mixture will remain blue colouration if reducing sugars are not present.

Lugol Iodine Test