Starch and Sugar - Test Effects

Effect of heat on starch
- obtain a slice is bread ( a slice of potato can also be used).
- place the slice in a very hot oven or a toaster.
- leave until slice turns to light brown.

Observation:
Light brown colour will be observed. The product is called dextrin. The process is known as dextrinization.

Effects of moist heat on starch
1. Place 2 table spoonfuls of corn starch paste in a bowl.
2. Add 6 table spoonfuls of cold water.
3. Mix thoroughly to obtain a slightly liquid consistency.
4. Pour boiling water rapidly into the mixture.

Observation:
The starch will swell and a jelly substance is formed. The process is gelatinization. The product is a gel.

Effect of moist heat on sugar:
- pour about 15ml of water into a sauce and add about 30g of sugar.
- heat gently.
- continue heating until syrup is formed.

Observation:
The syrup is formed as the liquid evaporates.

Food that can be used for simple sugar test are table sugar, honey, fruits for example ripe bananas.

Fehling's Test:
1. Place about 5ml of 5% sugar solution in a test tube.
2. Prepare the Fehling's solution by adding equal amounts of Fehling's solution A (copper sulphate in water) and B ( sodium potassium tartrate and sodium hydroxide in water).
3. Add 5ml of Fehling's solution into the sugar solution.
4. Place the tube into a beaker half-filled with water.
5. Heat the beaker gently to boil.

Observation:
An orange or brick-red precipitate will be formed. This shows the preens of a simple sugar.

Benedict's Test:
This is similar to Fehling's Test. It is however more sensitive.
- place about 5ml of 5% sugar solution in a test tube.
- add equal amount of Benedict's solution.
- boil as with the Fehling's test. Allow to stand.
- observe a red, orange or yellow precipitate that is formed. This shows the presence of a simple sugar.

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