19 BREAKDOWN OF STARCH TO SUGAR FEHLINGS TEST FOR REDUCING SUGARS Starch can be recognized by the deep blue colour which develops when it is in contact with iodine solution This is a very sensitive test Sugar does not react with iodine but sugar will reduce copper II in Fehlings solution to red copper I oxide and this is also a sensitive test Starch does not react with Fehlings solution Saliva contains enzyme catalysts which convert starch to sugar This experiment investigates the progress of this reaction Put about 10 mL of dilute starch solution into a testtube Add to this 1 mL of saliva and stir this into the starch solution Record the time of adding the saliva At 5minute intervals remove 2 or 3 drops by means of a dropper and put them on a clean white tile taking care to keep them from running into each other The dropper must be washed well between each test Put a little iodine solution on each drop The decreasing intensity of the blue colour indicates that starch is being used up Test for increasing amounts of sugar at the same time as testing for starch To do this put 2 or 3 drops of the reaction mixture into a small testtube Add 3 mL of Fehlings solution and warm this mixture almost to boiling point The test should show that the amount of sugar is increasing The enzyme in the saliva is therefore slowly breaking starch down into sugar which is a smaller molecule In a previous experiment yeast was used to break down sugar into ethanol which is an even smaller molecule Living yeast which is a variety of fungus produces enzymes which act as catalysts in the conversion C6H12O6  2C2H5OH  2CO2