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Testing for the presence of proteins - Biuret test . Show students the available foods for testing. Ask them which ones they expect to contain protein. Demonstrate to students how to perform the test. Put a food item containing protein into a test tubes (i.e. milk or tofu). If it is not a liquid, add some water and mash it well. Also set up a control, a test tube containing a liquid that does not contain protein (i.e. water). Add about 2ml of Biuret reagent to the test tube. 1. If the food to be tested is liquid, go to 2. If the food to be tested is solid, make an extract. Grind crush or chop a small amount and put into a test tube to a depth of about 2cm. Add a similar amount of distilled water and stir with a glass rod. Allow to stand for a few minutes. 2. Draw up some of the clear liquid into a pipette and then First, prepare test solution by grinding vitamin C reagent tablet into a powder using a mortar and pestle or back of a spoon. Pour powder into dropper bottle and add 30ml (1 oz.) of distilled water. If testing more than one liquid, label each test tube with a marker. Fill each with 50 drops of blue vitamin C indicator solution. Nutrient solutions to be tested (made from foods you wish to test for sugar, starch, protein, fat, and vitamin C content). Food Test 1: Sugar test-Benedict's solution Benedict's solution is used to test for simple sugars, such as glucose. Put different food solutions in each cup, e.g. corn starch in water, flour in water, milk, and water. Using the dropper, add a drop or two of the iodine solution to each cup. Place a slice of a potato on a paper towel atop a paper plate and add a drop of the iodine solution to the potato slice. Note the color change. Place foods in separate test tubes. if the food is liquid, pour enough to just cover the bottom of the glass. If the food is solid (e.g., banana, apple, potato chips), crush a small amount and add. enough water to cover the bottom of the tube. Iodine test for starch the most followed method to analyze the presence of starch in the given food material. When iodine solution is mixed with starch it turns from brown to dark blue. As this happens with very small amounts of starch, iodine test is a sensitive one. Testing for starch. Glucose is sweet and dissolves in water while starch is not sweet and does not dissolve well in water. A further test to distinguish starch from glucose is to shine a beam of light through 'solutions' of each. This is also called the Tyndall Beam Effect. Dispersal only happens in starch as the large starch molecules are big enough to affect the light. This is a physical test. A chemical test for starch is to add iodine solution (red) and see if it turns blue/black in colour. It is possible to distinguish starch from other carbohydrates using this iodine solution test. For example, if iodine is added to an peeled potato then it will turn black. You could demonstrate the effect of iodine solution on starch by adding a few drops of solution to a starch powder or starch suspension in a boiling tube. You can then discuss the fact that this colour change might be hard to see in a dark green leaf until the chlorophyll is removed. The iodine turned from a red/yellow colour to a blue-black colour. The iodine turned from a red/yellow colour in certain places to a blue-black colour, where starch is stored. The iodine turned from a red/yellow colour to a blue-black colour. Query: how do you test for starch in a food
Put different food solutions in each cup, e.g. corn starch in water, flour in water, milk, and water. Using the dropper, add a drop or two of the iodine solution to each cup. Place a slice of a potato on a paper towel atop a paper plate and add a drop of the iodine solution to the potato slice. Note the color change.