Food tests: Required Practical 4 Sunday, 09 December 2018 Food tests: Required Practical 4 Key Questions What is the basic structure of carbohydrates, lipids and proteins? What are the roles of carbohydrates, lipids and protein in the body? How can we test for carbohydrates, lipids and protein? Starter: What is the function of the following molecules in the body? Carbohydrate Fat Protein Challenge: name a disease caused by having either too much or too little of each of these nutrients. 

Carbohydrates Contain carbon, hydrogen and oxygen Made up of sugar units Substrate for respiration – energy release Simple Sugars One or two sugar units Immediate energy Complex carbohydrates Long chains of sugar units Slow release energy Sucrose Glucose Fructose

Testing for Carbohydrates Glucose Blue Benedict’s solution turns orangey-red when it is boiled with glucose. Starch Orangey-brown iodine turns blue-black when it reacts with starch. chopped up food hot water drop iodine solution onto the food heat black = starch

Lipids Contain carbon, hydrogen and oxygen Fats (solids) and oils (liquids) Glycerol +3 fatty acids (chain length and saturation varies) Energy store, cell membranes, hormones, nervous system Insoluble in water

Testing for Lipids A red stained oil layer, floating on the water surface is produced if lipids (fat) is present filter grind food Add distilled water then stir add 3 drops Sudan III Red stained floating layer = fat

Protein Contain carbon, hydrogen, oxygen and nitrogen Long chains of amino acids folded into a specific 3D shape Structural (form tissues) or metabolic (enzymes, hormones, antibodies)

Testing for Protein In the Biuret test the blue solution turns purple. potassium hydroxide copper sulphate shake purple = protein chopped up food

Plenary: For each food, decide on the chemicals found in them. 8A What’s in food? Plenary: For each food, decide on the chemicals found in them. Food sample Test Result Iodine solution orangey-brown Benedict’s test blue Biuret test purple Ethanol test cloudy white Plenary Protein Fats Starch Glucose

Food sample Test Result Iodine solution blue-black Benedict’s test 8A What’s in food? Food sample Test Result Iodine solution blue-black Benedict’s test blue Biuret test Ethanol test clear Protein Fats Starch Glucose

Food sample Test Result Iodine solution orangey-brown Benedict’s test 8A What’s in food? Food sample Test Result Iodine solution orangey-brown Benedict’s test orangey-red Biuret test blue Ethanol test clear Protein Fats Starch Glucose

Food sample Test Result Iodine solution orangey-brown Benedict’s test 8A What’s in food? Food sample Test Result Iodine solution orangey-brown Benedict’s test orangey-red Biuret test blue Ethanol test clear Protein Fats Starch Glucose

Exam question A student is analysing the nutrient content of egg whites. Fully describe an investigation that the student could carry out to find out if protein is present in a sample of the egg whites. (6 marks)

Mark scheme Level 0 – There is no relevant information. (no marks) Level 1 – There is a brief description of how to carry out the investigation. (1 to 2 marks) Level 2 – There is some description of how to carry out the investigation but some details are missing. (3 to 4 marks) Level 3 - There is a clear and detailed description of how to carry out the investigation. (5 to 6 marks) Here are some points your answer may include: Grind up a sample of the egg white using a pestle and mortar. Put the sample into a beaker and add some distilled water. Stir well with a glass rod to allow some of the food to dissolve in water. Filter the mixture through a funnel lined with filter paper. Transfer 2 cm3 of the filtered solution into a clean test tube. Add 2cm3 of Biuret solution and gently shake the test tube. If the food sample contains protein, the solution will change from blue to pink to purple. If no protein is present, the solution will stay bright blue.