How to Determine/Analyze Colours in Food Samples

Colour determination or analysis in food samples can be carried out in the laboratory using simple chromatographic methods.

AIM: To determine the colour used in production of a food sample 

PRINCIPLE: The addition of colour to food sample is a normal routine activity in the industry, Hence there are needs for colour verification in food samples in other to prevent addition of excess or poisonous colours. The first step is the extraction of the colour from the food sample using strong bleaching agent eg Glacial acetic acid. The addition of glacial acetic acid bleaches the colour of the food sample, which is then absorbed by a thread. The colour is extracted from the thread using Concentrated Ammonia and transferred to a paper chromatograph and determined in the presence of other standards. 

REAGENTS: Glacial Acetic acid, Concentrated Ammonia, 1% Ammonia, colour Standards, distilled water. 

APPARATUS: Paper Chromatograph, 50ml Beaker, 1000ml Beaker, fume cupboard, clips. 

GENERAL PROCEDURE: 

i) Extraction of colour from the food sample. 

ii) Identification of the extracted colour by paper chromatography. 

i) Extraction of Colour: 

Pure knitting wool is first boiled in dilute ammonia and then in water. 

For soluble foods like soft drinks, lollies (Lollipops), boiled sweets, jam, table jelly, etc

a) 3ml of acetic acid is added to about 20ml of the liquid food (The acid enables the colour to be absorbed by the knitting wool by bleaching it from the food) in a 50ml Beaker.

b) The parboiled knitting wool is placed into it and the setup is boiled for 5minutes on a water bath to dye the wool with colouring matter. After which, the wood is washed thoroughly under tap water to remove natural colours and food particles. Then the wool is soaked in concentrated ammonia to extract the colour.

c) Evaporate the solution on a water bath in a fume cupboard to leave a residue. 

For Solid samples: 

a) A knitting wool is placed inside a 50ml beaker v 0.5-1.5g of sample is weighed into the 50ml Beaker

b) 2ml of glacial acetic acid is added and left over night 

c) Wash the knitting wool under running water tap thoroughly to remove natural colours and food particles. 

d) Place the knitting wool in a 50ml Beaker, then add 4ml of concentrated ammonia to extract the colour. 

e) Evaporate the solution on a water bath in a fume cupboard to leave a residue.

This is then transferred to the paper chromatography.👇👇👇

CHROMATOGRAPHIC PROCEDURE FOR IDENTIFICATION OF FOOD COLOUR