Carbohydrates Tests Flashcards
(17 cards)
What is the first step in biochemical tests for food samples?
Add 2cm³ of the food sample to be tested (needs to be in liquid form to begin with).
What reagent is used to test for reducing sugars?
Benedict’s reagent can be used to test for the presence of reducing sugars.
What types of sugars are considered reducing sugars?
All monosaccharides and some disaccharides (e.g. maltose) are reducing sugars.
What is Benedict’s reagent composed of?
Benedict’s reagent is an alkaline solution of Copper(II) Sulfate.
What happens when a reducing sugar is added to Benedict’s reagent and heated?
It forms an insoluble red precipitate (copper(I) oxide).
What indicates a positive result in the Benedict’s Test?
If the solution turns brick red (orange-brown), then a reducing sugar is present.
What is the procedure for testing reducing sugars?
Add 2cm³ of food sample to 2cm³ of Benedict’s Reagent and heat in a water bath for 5 minutes.
What should be done if the color does not change from blue to brick red?
A reducing sugar is not present.
How do you test for non-reducing sugars?
Add 2cm³ of dilute hydrochloric acid to another 2cm³ of the food sample and heat for 5 minutes.
What is the purpose of adding dilute hydrochloric acid?
It hydrolyses the disaccharides and polysaccharides into their constituent monosaccharides.
What is done after adding hydrochloric acid to neutralize the solution?
Add sodium hydrogencarbonate to neutralise the test tube.
How do you confirm the solution is neutralized?
Use pH paper to check that the solution is neutralised.
What is the final step to retest for non-reducing sugars?
Add 2cm³ of Benedict’s Reagent to the neutralised solution and heat for 5 minutes.
What indicates the presence of a non-reducing sugar?
A color change from blue to brick red (orange-brown) in the Benedict’s Reagent.
What chemical test is used for starch?
Iodine/potassium iodide is used for testing starch.
What indicates the presence of starch in a solution?
If the solution turns blue/black from orange-brown, then starch is present.
Overall, how to test for non-reducing sugars?
Add dilute hydrochloric acid to a new sample,
Neutralise with sodium hydrogencarbonate,
Perform Benedict’s test on hydrolysed solution,
if a colour change occurs and a brick red precipitate forms then non - reducing sugars were present
