Table 1. Iodine test. Results Page:-3 Tube Substance Color Starch Present? 1 Soya bean White No 2 Peanut Purple No 3 Milk White No 4 Onion Transparent yellow No 5 Potato Dark green Yes 6. Starch Blue Table 2. Fehling's test. Tube Substance 1 Soya bean Color Light brown Reducing Sugar Present? Yes 2 Peanut Dark brown Yes 3 Milk Light brown Yes 4 Onion Radish brown Yes 5 Potato Yellowish Yes 6. Glucose Orange Table 3. Millon's test. Tube Substance Color Protein Present? 1 2 Soya bean Peanut White precipitate No Brown precipitate Yes 3 Yes Milk 4 Onion Light orange precipitate Light orange precipitate No 5 Potato Brown precipitate No Egg White Table 4. Sudan III test. Brown precipitate Tube Substance Color Fat Present? 1 Soya bean Oll layer not visible No 2 Peanut Oil layer not visible No 3 Milk Oil layer not visible No 4 Onion Oil layer visible Yes 5 Potato Oil layer visible No 6. Cooking oil Oll layer visible Read the page 1,2 and 3 carefully Lab Report Page:-2 If a yellow/green precipitate appears, this indicates that a reducing sugar is present. If the solution You have to make two parts one is discussion/ analysis and another one is conclusion based on these remains blue, this means an absence of a reducing sugar. Some disaccharides (e.g. sucrose) and all polysaccharides (e.g. starch) are not reducing sugars because they do not have free aldehyde experiment procedure and results. groups. 1. Discussion: In discussion, you have to explain the results that are given in page:-3 based on the experiment procedure. 2. Conclusion: Conclusion must be in 2 or 3 lines. EXPERIMENTI Page:-1 DETECTING COMPOUNDS MADE BY LIVING THINGS INTRODUCTION Specific compounds are necessary for life processes such as growth, development, reproduction maintenance and repair. Scientists have developed a series of chemical tests to determine the presence and absence in food samples of the building blocks of living things. In testing the substances and food available, you should realize that the materials had a biological origin-they were made by producers or consumers. There are many compounds present in living organisms. However, you will perform tests for only four of these compounds: sugar, starch, protein and fat. These tests are generally qualitative tests for the four substances. A qualitative test is one in which you observe the presence (or absence) of a substance. A few of the tests also indicate the relative amount of a substance present by the intensity of the color of the test solution. In this laboratory exercise, you will use specific chemical tests to verify the presence of starch, sugar, protein, and fat in food samples. PROCEDURE A. Tests For Carbohydrate (4) Test for Starch Add 3 drops of iodine solution into a test tube containing some starch solution. Note the change that takes place. For the iodine test, if the food turns pale brown, starch is not present (b) Test for Glucose Add some glucose solution into a test tube. Using Pasteur pipettes, add 10 drops of Fehling's solution I and 10 drops of Fehling's solution Il into the test tube. Heat the solution in a water bath at 90 °C and note the change in color. Fehling's Test This is a reducing sugar (e.g. glucose) test that depends on a free aldehyde group: 0=C) Monosaccharides and some disaccharides have a free aldehyde group and consequently will react to give a positive Fehling's test. Such a sugar acts as a reducing agent and is called a reducing sugar. The reaction goes like this: Fehling's reagent + om Fehling's reagent om (died form) (reducing sugar) (reduced form) (c) Test for Sucrose Prepare two test tubes containing a solution of common sugar. To one of the tubes, add 4 drops of dilute HCI (0.1 M). Place both tubes in a boiling water bath for 5 minutes. Leave the tubes to cool down for a while and then add Fehling's solutions I and II as described in (b). Is there a difference in the color between the two tubes? Explain your observation. B. Test For Protein 1. To a test tube (tube #1), add some egg white (or bovine serum albumin, BSA, solution) which has been diluted 5 times with deionised water. 2. To a separate tube (tube #2), add some deionised water. 3. To each of the two test tubes, add 5 drops of Millon's reagent (Caution: Poisonous!) using a Pasteur pipette. Heat the tube in a 90 °C water bath. If protein is present, the Millon's reagent will turn red with heating. What was the purpose of tube #2? C. Test For Fat Fat is a hydrophobic molecule consisting of a glycerol molecule joined to three fatty acids. The important functional groups involved in a fat are these: the carboxyl group (-COOH) and the hydroxyl group (-OH). The hydroxyl groups of the glycerol react with the carboxyl groups of the fatty acids in a condensation reaction, so these functional groups are no longer available for a test reaction. Instead, the Sudan III test depends on the detection of the hydrocarbon groups remaining. The colored dye, Sudan III, and the hydrocarbon groups are nonpolar and stick tightly together in polar surroundings. Simple hydrophobic interaction is thus the basis of this test. 1. Add some vegetable oil into a test tube. Using a Pasteur pipette, add about 10 drops of Sudan III. Shake the tube for 3 minutes and allow it to stand for half an hour. Note the change in color. 2. Alternative Test: Put a drop of oil on a filter paper, and on another filter paper put a drop of deionised water. Allow the filter papers to dry. Hold the paper up against the light and examine for the grease spot which indicates the presence of fat. Note the difference in the two papers. What was the purpose of the "water" spot? D. Testing Unknowns You are provided with several types of food: peanuts, milk, extract of soya bean, of onion and of potato. Place a small sample of each of these food types, in a clean test tube and test it for sugar, starch, fat and protein. Be sure to mix all the components thoroughly so that you do not get a false negative. Record the results in the following tables.