FOOD TESTING LAB

Introduction:

The nutrients in the food you eat supply your body with energy for growth and repair. These principle substances include carbohydrates, proteins, fats, minerals and vitamins.

Carbohydrates make up a group of organic compounds that include sugars and starches, which are important in supplying your body with energy. Some starches provide your body with indigestible fiber, or roughage, which aids digestion.

Proteins are organic compounds important for growth and repair. Lipids (e.g. fats) are organic compounds that can supply as much as four times the amount of energy as carbohydrates or proteins.

Vitamins aid in growth and also help to protect the body from disease.

Using Chemical Indicators

We can test for the presence of these important compounds in food by using chemical reagents that react in predictable ways in the presence of these nutrients.

Work in an area appropriate for handling chemicals that may stain furniture or the floor if spilled. Wear proper safety equipment including goggles, rubber gloves and a lab apron.

Outlined below are just the basic test procedures required to use these test solutions.

Supplies needed:

• 12 x 75mm test tubes. One per test sample.
• Test tube clamps.
• Test tube rack.
• Lab Thermometer.
• Mortar and Pestle.
• Droppers.
• Small beakers or glass jars.
• Glass marking pen (Sharpie or China marker).
• Hot water.
• 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. 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.

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 Benedict's 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.
5. Note any color change. If sugar is present solution will turn green, yellow, or brick-red, depending on sugar concentration.

Food Test 2 Starch - Lugol's iodine

Lugol's iodine solution is used to identify the presence of starch. Lugol's solution is yellow-brown but, when it reacts chemically with starch, a blue-black substance called iodide starch is produced.

What to do.

1. To a test tube, add 40 drops of liquid to be tested.
2. If testing more than one liquid, label each test tube with a marker.
3. Add 2 drops of Lugol's iodine solution to each test tube. Shake gently to mix.
4. Note any color change. If starch is present a blue-black precipitate will form.

Food Test 3 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.

1. To a test tube, add 40 drops of liquid to be tested.
2. If testing more than one liquid, label each test tube with a marker.
3. Add 3 drops of Biuret reagent solution to each test tube. Shake gently to mix.
4. Note any color change. Proteins will turn solution pink or purple.

Food Test 4 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.

1. To a test tube, add equal parts of test liquid and water to fill about half full.
2. If testing more than one liquid, label each test tube with a marker.
3. Add 3 drops of Sudan III stain to each test tube. Shake gently to mix.
4. A red-stained oil layer will separate out and float on the water surface if fat is present.

Food Test 5 Vitamin C

VITAMIN C REAGENT (dichlorophenolindophenol) indicator solution is blue. A colorless end point will be reached when this indicator is added to a solution containing vitamin C

What to do.

1. First, prepare test solution by grinding vitamin C reagent tablet into a powder using a mortar and pestle. Pour powder into dropper bottle and add 30ml of distilled water.
2. If testing more than one liquid, label each test tube with a marker. Fill each with 50 drops of liquid to be tested (e.g. orange juice).
3. Now add blue test solution one drop at a time to the sample in the test tube.
4. Count drops until dark blue color turns clear. This is your end point.