Food Test 1: Sugar test-Benedicts solution Benedicts solution is used to test for simple sugars, such as glucose. It is a clear blue solution of sodium and copper salts. In the presence of simple sugars, the blue solution changes color to green, yellow, and brick-red, depending on the amount of sugar. What to do. Mix small amount of each food sample with distilled water to make a test liquid. To a test tube, add 40 drops of liquid to be tested. If testing more than one liquid, label each test tube with a marker. Add 10 drops of Benedicts solution to each test tube. Carefully heat the test tubes by suspending in a hot water bath at about 40-50 degrees celsius for five minutes. Note any color change. If sugar is present solution will turn green, yellow, or brick-red, depending on sugar concentration. Food Test 2: Protein - Biuret solution Biuret solution is used to identify the presence of protein. Biuret reagent is a blue solution that, when it reacts with protein, will change color to pink-purple. What to do. To a test tube, add 40 drops of liquid to be tested. If testing more than one liquid, label each test tube with a marker. Add 3 drops of Biuret reagent solution to each test tube. Shake gently to mix. Note any color change. Proteins will turn solution pink or purple. Food Test 3: Fat - Sudan III stain Sudan III is used to identify the presence of lipids in liquids. It will stain fat cells red. What to do. To a test tube, add equal parts of test liquid and water to fill about half full. If testing more than one liquid, label each test tube with a marker. Add 3 drops of Sudan III stain to each test tube. Shake gently to mix. A red-stained oil layer will separate out and float on the water surface if fat is present. Food Test 4: Vitamin C Vitamin C Reagent (dichlorophenolindophenol) indicator solution is blue. A colorless end point will be reached when a solution containing vitamin C (such as orange juice) is added to this indicator. What to do. 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. Now add juice one drop at a time to the indicator solution in the test tube. Count drops until dark blue color turns clear. This is your end point. Compare different juices. Those that require more drops to reach the clear end point are LOWER in vitamin C. Food Test 5: How Much Sugar Is In My Soda? To measure the amount of sugar in a solution, be it juice, Coca Cola, etc., you use a Brix hydrometer, called Brix as the food industry uses the term to designate the sugar percentage contained in a liquid. The hydrometer is placed to float in a solution, and the point at which the liquid’s surface touches the stem of the inserted hydrometer incidates the percentage of sugar in the liquid. What you need. BRIX hydrometer, range 0-35 degrees Graduated cylinder, 500ml, to contain the liquid Reading the Brix Scale. The Brix scale gives a direct reading of grams of sugar per 100 grams of pure water. So, for example, say a 20oz (591ml) bottle of root beer gives a measurement of 12 Brix. How much sugar in the entire bottle? Here is the equation: 12g/100ml = Xg/591ml. Solving for X gives X=70.92g sugar. Tips on using the Hydrometer. Soda should be degassed before making a measurement. The tiny bubbles in carbonated beverages tend to stick to the hydrometer and add unwanted buoyancy. You can degas your soda sample with gentle heating or just leaving the soda out until it goes “flat”. Be sure the soda is at room temperature before taking a reading. Hydrometers are most accurate when used at the calibrated temperature marked on the scale. Most hydrometers sold by the Science Company are for use at 20°C (68°F).
Posted on: Sat, 15 Mar 2014 08:25:23 +0000
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