1.13: chemical reagents core practical

What is the aim of this experiment?

To investigate the use of chemical reagents to identify starch, reducing sugars, proteins and fats

What test is used for starch?

Iodine turns from yellow/orange to black

What is the method to identify starch?

Place one spatula of the food sample on a dish. Using a dropper, place a few drops of opine solution onto the food and record a change in colour

What is used to identify reducing sugars?

Benedict’s solution

What sugars are reducing sugars?

Glucose, fructose, lactose

What sugars are non-reducing sugars?

Sucrose, stachyose

What is the method for identifying reducing sugars?

Place two spatulas of the food sample into a test tube and add 1cm³ depth of water to the tube. Stir to mix. Add an equal volume of Benedict’s solution and mix. Place the test tube in a water bath at 95 degrees Celsius for a few minutes then record the colour of the solution

If there is glucose present, what colour should the solution turn?

From blue to brick red

What is the test for proteins?

Biuret

What is the method for testing if protein is present?

Add a few spatulas of the food sample to a test tube. Then add several drops of Biuret solution to the food sample and record a change in colour

What change in colour will we see if protein is present?

The solution turns from blue to purple when mixed with protein

What is the test for lipids?

Place two spatulas of the food sample into a test tube and add 2cm³ of ethanol. Shake the tube vigorously and allow the contents to settle. Then add an equal volume of distilled water.

What will i see if there are lipids present?

A milk white emulsion will form if the substance contains lipids

Examples of foods which contain starch

Rice and breakfast cereal

Examples of foods which contain protein

Beef

Examples of foods which contain lipids

Beef, vegetable oil and breakfast cereal

Examples of foods which contain reducing sugars

Breakfast cereal