Mandatory experiments on Food

Test for reducing sugar

Test for fats

Test for protein

Test for starch

Food Tests – Summary Chart Test for Materials Method Positive Results Starch Iodine Solution Add iodine to the food sample A blue/black colour Reducing sugar (Glucose) Benedict's Solution Add to sample and warm gently A brick red colour Protein Copper sulphate (CuSO4) and sodium hydroxide (NaOH) Biuret solution Add some NaOH to the moist food. Then gently pour CuSO4 solution down the side of the tube A violet colour Fat Brown Paper Rub the food onto the paper, warm gently to dry and hold the paper up to the light A translucent spot Vitamin C DCPIP Add to moist food or fruit juice A change from blue to pink or colourless

Experiment Questions Food Tests

Food Tests For what is the Biuret test (copper sulphate and sodium hydroxide solutions) used in the biology laboratory? Test for protein

Food Tests For what is the Benedict’s (or Fehling’s) test used in the biology laboratory? Test for reducing sugar

Food Tests For what purpose did you use brown paper or Sudan III in food testing? To test for Fat / Lipid / Oil

Food Tests What reagent or chemicals did you use to test for protein? Biuret OR NaOH and CuSO4

Food Tests Is heat necessary in the test that you carried out to test for protein? No

Food Tests What colour change indicates the presence of protein? From blue to purple / violet

Food Tests Name the test or name the chemical used to test a solution for the presence of glucose (reducing sugar). Clinistix / Benedicts / Fehling’s / Copper sulphate

Food Tests What colour change indicates a positive result for the presence of glucose? (Clinistix) Orange to Blue or (others) Blue to Red

Food Tests Is heat necessary to test a solution for the presence of reducing sugar? Yes

Food Tests For which purpose did you use Biuret solution or alkaline copper sulphate in food testing? To test for (soluble) protein

Food Tests State a use for the Biuret test in the biology laboratory. To detect presence of protein

Food Tests What is the initial colour of the reagent or chemicals used to test for protein? Blue

Food Tests Was there a colour change in the control experiment when testing for protein? No

Food Tests Name the test or give the chemicals used to test a sports drink for the presence of protein. Biuret Test / Sodium Hydroxide & Copper sulphate

Food Tests If protein is present in a drink, what colour change would you expect to see? In your answer give the initial and final colour of the test solution. Blue to violet /purple / lilac

Is heat necessary for the test for protein? No Food Tests Is heat necessary for the test for protein? No

Food Tests For what purpose did you use Fehling’s solution or Benedict’s solution in the course of your practical activities? To check for Glucose / reducing sugar

Food Tests For which purpose did you use Brown paper or Sudan III in food testing? To test for fat (or lipid or oil)

Food Tests—Reducing sugar (i) Name the reagent(s) used. (ii) State the initial colour of the reagent. (i) Benedict’s/ Fehlings I and II, (ii) Blue

Food Tests—Reducing sugar State whether the test requires heat. Yes

Food Tests—Reducing sugar What colour indicates a positive result? Brick-red/orange

Food Tests—Protein (i) Name the reagent(s) used. (ii) State the initial colour of the reagent. (i) Biuret solution / CuSO4 + NaOH (ii) Blue/ light blue

State whether the test requires heat. No Food Tests—Protein State whether the test requires heat. No

What colour indicates a positive result? Purple / violet Food Tests—Protein What colour indicates a positive result? Purple / violet

Food Tests (i) Name a test to show the presence of a reducing sugar (e.g. glucose). (ii) Describe how you would carry out this test. (i) Benedict’s/ Fehling’s (ii) Dissolve sample in water or put in test tube / add reagent / heat / don’t boil / observe change or state result (brick-red-orange precipitate)

Food Tests (i) Name a test for protein. (ii) Describe how you would carry out this test. (i) Biuret test or named chemicals (ii) Add biuret reagent (or sodium hydroxide and copper sulfate) / to sample / heat or shake / observe or record colour change (purple-violet)

Questions pg 13/14