To compare the reducing sugar content of dry raisin and fresh grape
i) Principle of Benedict’s test
Reducing sugar can reduce Cu2+ into Cu+ and form a bricked-red precipitate (copper(I) oxide) which is insoluble in water.
ii) Use of Benedict’s test
Benedict’s test can show the presence of reducing sugar (all monosaccharide and disaccharide, except sucrose). Add Benedict’s solution into food samples (solution). Then mix them up and put into a water bath for 5 minutes. If reducing sugar is presence, there will be bricked-red precipitate.
More is that, the variation of the color of the bricked-red precipitate can deduce the concentration of reducing sugar. The deeper the color of precipitate, the more the content of reducing sugar.
iii) Different concentration of glucose solutions as indicator Different concentrations of glucose solutions are prepared as indicator. Apply Benedict’s test on those glucose solutions and use the result to compare the result from grape or dry raisin. Thus, the content of reducing sugar can be estimated.
|2 pieces of fresh grape |20 pieces of dry raisin |Benedict’s solution |1.5% glucose solution |1 x 1 ml pipette | |2 x 5 ml pipettes |1 x pipette filler |Pestle and mortar |Electronic balance |Water bath |
1. 1 grape fruit was weighted.
2. Grape fruit juice was extracted by pestle and mortar.
3. 50ml of water was added.
4. 1ml of the solution was transferred into a test tube.
5. 9ml of water is added into the test tube in Step4.
6. 1ml of solution in Step5 was transferred into a test tube. 7. Step 1-6 were repeated by using dry raisin that having the same weight(8g) of grape fruit. 8. A series of standard solution of glucose with different concentration was prepared by following table1. | |Glucose (ml) |Water (ml)...