Food tests Investigating the presence of proteins, carbohydrates and fats in different foods You can test samples of foods to see whether they contain these three components. The tests are qualitative – they only tell you if the substance is there, not how much of it. Task 1 Here are some typical food samples – say which components you think they will contain: Fat Protein Starch Sugar crisps banana chicken breast cheddar cheese potato apple white rice chocolate egg white wholemeal bread © www.teachitscience.co.uk 2015 25026 Page 1 of 4 Food tests Practical work: food tests summary Lipids Translucent spot Rub a sample on filter paper, warm Non-drying grease spot shows lipid present Ethanol emulsification Stir tiny sample thoroughly with ethanol. Add water Milky if lipid present. Haze if trace only. Iodine test Add a few drops of iodine solution to solid Dark blue/black shows starch present fats/oils Carbohydrates starch The next two tests each need a small sample of the liquid produced when some of the food is stirred very thoroughly with water. Benedict’s test needs a beaker of boiling water. Proteins Biuret test Add Biuret reagent to test tube Purple colour shows protein, blue no protein Carbohydrates Benedict’s test Add Benedict’s reagent to test tube, place in boiling water bath Colour goes from clear blue → cloudy green, yellow, orange with increasing glucose sugar (glucose) © www.teachitscience.co.uk 2015 25026 Page 2 of 4 Food tests Results of food tests Fill in your observations and results for each food that you tested. Food tested lipids proteins starch glucose Comment on your findings: © www.teachitscience.co.uk 2015 25026 Page 3 of 4 Food tests Teaching notes Page 1 Use task 1 prior to carrying out the food tests, it could make a useful homework task. Page 2 The summary sheet is a handy reference for students when carrying out the food tests. Page 3 The final sheet can be used by students to record their observations. N.B. See CLEAPPS Hazcards to carry out a risk assessment before doing food tests with a class. www.cleapss.org.uk/ © www.teachitscience.co.uk 2015 25026 Page 4 of 4