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Food Groups Tests
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Testing for starch Method:
1. Mix small amount of each food sample with distilled water to make a test liquid. 2. To a test tube, add 40 drops of liquid to be tested. 3. If testing more than one liquid, label each test tube with a marker. 4. Add 5 drops of iodine solution to each test tube 5. Note any color change. If starch is present solution will blue/black
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Testing for (refined/ simple) sugars
Method: Mix small amount of each food sample with distilled water to make a test liquid. 2. To a test tube, add 40 drops of liquid to be tested. 3. If testing more than one liquid, label each test tube with a marker. 4. Add 10 drops of Benedict's solution to each test tube. Carefully heat the test tubes by suspending in a hot water bath at about degrees celsius for five minutes. 5. Note any color change. If sugar is present solution will turn green, yellow, or brick-red, depending on sugar concentration.
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Testing for protein Method: 1. Mix small amount of each food sample with distilled water to make a test liquid. 2. To a test tube, add 40 drops of liquid to be tested. 3. If testing more than one liquid, label each test tube with a marker. 4. Add 10 drops of Biuret’s solution to each test tube 5. Note any color change. If protein is present solution will turn purple
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Testing for lipids Add 10 drops of ethanol to a few drops of the unknown substance in a test tube 2. Shake well 3. Add 10 drops of distilled water to the test tube 4. A positive result will result in a cloudy white suspension forming at the top of the solution.
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1) Carbohydrates Testing for starch
Use a spotting tile with the food samples. Add 2 drops of iodine solution to each food sample. Which of these foods contain starch? Record results. A colour change from orange to blue-black shows the presence of starch.
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Testing for glucose Use 1 spatula of glucose powder in a third of a test tube of water. Dissolve. Put in 10 drops of Benedict’s solution. Heat carefully (in & out of a Bunsen burner flame) Note your result. A colour change from blue, through murky green to yellow/orange/red shows the presence of a simple sugar.
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2) Fats & oils (lipids) A white (milk-like) emulsion indicates the presence of fats or oils.
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3) Test for Proteins Check!
If the mixture turns purple, protein is present. Use a pestle & mortar to grind up samples of the food (separately). Put the food sample into a test tube with 10 drops of Biuret solution. Check! HAZARD! Biuret solution is corrosive. Wear eye protection throughout the test. Remove only when all packing away is complete.
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