What are the two categories of sugars that can be tested for?

Reducing sugars and non-reducing sugars.

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Which sugars are classified as reducing sugars?

Monosaccharides and some disaccharides such as maltose and lactose.

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Which sugars are classified as non-reducing sugars?

Some disaccharides such as sucrose and all polysaccharides.

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How can you test for reducing sugars?

  1. Add Benedict's reagent to the sample.
  2. Heat the mixture in a water bath.


If reducing sugars are present, the mixture will change from a blue solution to a brick red precipitate. 

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What does a blue colour indicate in the reducing sugar test?

No reducing sugar is present.

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What does an orange colour indicate in the reducing sugar test?

A medium concentration of reducing sugar.

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What are the quantitative methods to determine reducing sugar concentration?

Using a colorimeter or filtering and weighing the precipitate.

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What is the first step to test for non-reducing sugars?

Carry out the test for reducing sugars.

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How can you test for non-reducing sugars?

  1. Carry out the test for reducing sugars.
  2. Add the sample to some dilute hydrochloric acid.
  3. Heat the mixture in a water bath. 
  4. Neutralise the mixture by adding sodium hydrogencarbonate solution. 
  5. Retest the sample using the test for reducing sugars.

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How can you test for starch?

Add iodine solution to the sample and if starch is present, the solution will turn from orange to blue-black. 

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