Testing for carbohydrates Flashcards
What is the name of the test for carbohydrates?
Benedict’s test for reducing sugars
What are reducing sugars?
Reducing means chemistry reduction is a reaction involving the gain of electrons. All monosaccharides and some disaccharies (e.g. maltose and lactose) are reducing sugar. This means they can donate electrons or reduce another molecule or chemical.
What is the Benedict’s reagent?
alkaline solutions of Copper(II) sulfate.
What is the test for?
reducing sugars
How is the test carried out?
1) Place the sample to b etested in a boiling tube. If it is not a liquid grind it up or blend it in water. 2) Add an equal volume of Benedict’s reagent. 3) Heat the mixture gently in a boiling water bath for five minutes
What are the indications of a postive result?
Reducing sugars will react with the copper ions in the benedicts reagent.
Reduces the blue Cu2+, reducing them to brick red Cu+ ions.
Brick red precipitate is formed.
Depends on the concentration of the reducing sugars presents, as the less blue Cu2+ ions makes the test qualitative.
How is the Benedict’s test for non-reducing sugars?
Boiled with hydrochloric acid and it will then give a positive result when warmed with Benedict’s solution. This is because the sucrose has been hydrolysed by the acid to glucose and fructose.
What are the different colurs that indicate the amount of non-reducing sugar present?
blue - none
green - very low
yellow - low
orange - medium
red - high
What is the test for starch?
Iodine test.
A few drops of iodine dissolved in potassium iodide solution are mixed with a sample.
If the solution changes colour from yellow to brown to purple/black starch is present in the sample.
What are the advantages of reagents strips and what are the other methods of determing the amount of sugars?
Colour-coded chart, the concentration of the sugar can be determined
colorimetry.
