To compare quantitatively the concentrations of glucose and other reducing sugars in samples of fresh orange, lemon and grapefruit juice. The standard test for glucose (and other reducing sugars) is to use Benedict's reagent
Tessie Taylor 12 I
Glucose concentrations in orange, lemon and grapefruit juice
Introduction
In this experiment, I am going to have to compare quantitatively the concentrations of glucose and other reducing sugars in samples of fresh orange, lemon and grapefruit juice. The standard test for glucose (and other reducing sugars) is to use Benedict’s reagent. Benedict’s reagent is copper (II) sulphate in an alkaline solution, and so has a blue colour to it. If it is added to a reducing agent, its Cu2+ ions will be reduced to Cu+, resulting in the precipitant changing colour to the red of copper (I) sulphate. Reducing sugars have this effect on Benedict’s reagent because they have a –C=O group somewhere in their molecules which can contribute an electron to the copper, hence the name “reducing sugars” (1). If a reducing sugar is present when Benedict’s solution is added, the solution will change colour through green, yellow and orange, to brick red as the copper (I) sulphate forms a precipitant.
All fruit contains the sugars glucose and fructose. Fructose is an isomer of glucose, so both sugars have the molecular formula: C6H12O6. Both are monosaccharides, and are hexoses (they both have 6 carbon atoms in each molecule). Both glucose and fructose are reducing sugars, so I would really be finding the concentrations of both fructose and glucose in my fruit juices rather than just glucose, but for ease, I will only talk about glucose from now on.