biology food tests practical

includes how to do a couple 6 markers

first step of food tests

take food sample and grind with distilled water to make a paste then transfer to a beaker and add more distilled water, stir so the chemicals in food will dissolve in water. Filter solution. For each test add 2cm cubed of food solution.

Carbohydrates test (starch)

Add iodine solution (brown) to the filtered solution. A blue-black colour indicates the presence of starch.

Carbohydrates test (sugars)

Add ten drops of benedicts solution (blue), but test tube in beaker of hot water. Leave for five minutes if sugar is present benedicts colour will change.

Green = small amount of sugar

Yellow = more sugars

Red brick colour = lots of sugar present

Note - Only works for reducing sugars not non-reducing sugars like sucrose.

Protein test

Add Biuret solution (blue) to the food solution; if protein is present, the solution will turn purple.

Lipids

Grind food with distilled water but do not filter solution because lipids molecules can stick to filter paper.

Add two drops of ethanol and distilled water and shake lightly.

Lipids present = white cloudy emulsions.

6 Marker- Describe how to test a sample of food for protein, starch, and sugar. Give the colours that would be seen if the food sample contained protein, starch and sugar.

First, take your food sample and grind it with distilled water. Then filter it to get rid of any suspended food particles. #

Protein;

-add two drops of biuret solution to 2cm cubed of food solution

-biurets = blue

-if protein is present = purple

Starch

-add two drops of iodine (brown)

-if starch present = blue-black colour

Sugars

-add your test tube in a beaker of hot water

-add 10 drops of benedicts solution (BLUE) and wait five minutes.

-green colour= little concentration of sugar

-yellow colour= bit more sugar

-brick red colour = loads of sugar

-blue colour = no sugars

NOTE - this only works on reducing sugars not non-reducing sugars like sucrose.