test and experiment on food nutrients

4 Simple Chemical Tests for Food

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Simple chemical tests can identify a number of important compounds in food. Some tests measure the presence of a substance in food, while others can determine the amount of a compound. Examples of important tests are those for the major types of organic compounds: carbohydrates, proteins, and fats.

Here are step-by-step instructions to see if foods contain these key nutrients.

Benedict's Solution

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Carbohydrates in food can take the form of sugars , starches, and fiber. Use Benedict's solution to test for simple sugars, such as fructose or glucose. Benedict's solution doesn't identify the specific sugar in a sample, but the color produced by the test can indicate whether a small or large quantity of sugar is present. Benedict's solution is a translucent blue liquid that contains copper sulfate, sodium citrate, and sodium carbonate.

How to Test for Sugar

• Prepare a test sample by mixing a small amount of food with distilled water.
• In a test tube, add 40 drops of the sample liquid and ten drops of Benedict's solution.
• Warm the test tube by placing it in a hot water bath or container of hot tap water for five minutes.
• If sugar is present, the blue color will change to green, yellow, or red, depending on how much sugar is present. Green indicates a lower concentration than yellow, which is a lower concentration than red. The different colors may be used to compare the relative amounts of sugar in different foods.

You can also test for the amount of sugar rather than its presence or absence using density. This is a popular test for measuring how much sugar is in soft drinks .

Biuret Solution

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Protein  is an important organic molecule used to build structures, aid in the immune response, and catalyze biochemical reactions. Biuret reagent may be used to test for protein in foods. Biuret reagent is a blue solution of allophanamide (biuret), cupric sulfate, and sodium hydroxide.

Use a liquid food sample. If you are testing a solid food, break it up in a blender.

How to Test for Protein

• Place 40 drops of liquid sample in a test tube.
• Add 3 drops of Biuret reagent to the tube. Swirl the tube to mix the chemicals.
• If the color of the solution remains unchanged (blue) then little to no protein is present in the sample. If the color changes to purple or pink, the food contains protein. The color change can be a bit hard to see. It may help to place a white index card or sheet of paper behind the test tube to aid viewing.

Another simple test for protein uses calcium oxide and litmus paper .

Sudan III Stain

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Fats and fatty acids belong to the group of organic molecules collectively called  lipids . The lipids differ from the other major classes of biomolecules in that they are nonpolar. One simple test for lipids is to use Sudan III stain, which binds to fat, but not to proteins, carbohydrates, or nucleic acids.

You'll need a liquid sample for this test. If the food you are testing is not already a liquid, puree it in a blender to break up the cells. This will expose fat so it can react with the dye.

How to Test for Fat

• Add equal volumes of water (can be tap or distilled) and your liquid sample to a test tube.
• Add 3 drops of Sudan III stain. Gently swirl the test tube to mix the stain with the sample.
• Set the test tube in its rack. If fat is present, an oily red layer will float to the surface of the liquid. If fat is not present, the red color will remain mixed. You're looking for the appearance of red oil floating on water. There may only be a few red globules for a positive result.

Another simple test for fats is to press the sample onto a piece of paper. Let the paper dry. Water and volatile organic compounds will evaporate. If an oily stain remains, the sample contains fat. This test is somewhat subjective, because the paper may be stained by substances other than lipids. You can touch the spot and rub the residue between your fingers. Fat should feel slippery or greasy.

Dichlorophenolindophenol

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Chemical tests may also be used to test for specific molecules, such as vitamins and minerals. One simple test for vitamin C uses the indicator dichlorophenolindophenol, which is often just called "vitamin C reagent" because it's much easier to spell and pronounce. Vitamin C reagent is most often sold as a tablet, which must be crushed and dissolved in water just prior to performing the test.

This test requires a liquid sample, like juice. If you're testing a fruit or solid food, squeeze it to make juice or liquefy the food in a blender.

How to Test for Vitamin C

• Crush the vitamin C reagent tablet. Follow the instructions that came with the product or dissolve the powder in 30 milliliters (1 fluid ounce) of distilled water. Don't use tap water because it can contain other compounds that could affect the test results. The solution should be dark blue.
• Add 50 drops of vitamin C reagent solution to a test tube.
• Add a liquid food sample one drop at a time until the blue liquid turns clear. Count the number of drops required so you can compare the amount of vitamin C in different samples. If the solution never turns clear, there is very little or no vitamin C present. The fewer drops required to change the color of the indicator, the higher the vitamin C content.

If you don't have access to vitamin C reagent, another way to find vitamin C concentration is using iodine titration .

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• Tests Of Carbohydrates Fats And Proteins In Given Food Stuffs

Tests of Carbohydrates, Fats and Proteins in Given Food Stuffs

Carbohydrates provide energy to cells in the body. Protein is the major functional and structural component of all the cells of the body. Fats and oils are the highest energy sources that contain fatty acids which is essential for health and are not produced by the human body.

To detect the presence of carbohydrates, fats and proteins in the given food stuffs.

The presence of carbohydrates, fats and proteins in any food stuff is detected by performing the tests for proteins, fats and carbohydrates with the extract of the foodstuff. The advantage is these tests do not interfere with each other.

Test for Carbohydrates:

• Molisch’s test – Given sample food + Molisch’s reagent → Purple or violet ring confirms the presence of carbohydrate.
• Fehling’s test – Given sample food + Fehling’s reagent → Red precipitate confirms the presence of carbohydrates
• Benedict’s test – Given sample food + Benedict’s reagent → Red precipitate confirms the presence of carbohydrates.
• Tollen’s test – Given sample food + Tollen’s reagent → Silver mirror confirms the presence of carbohydrates.
• Iodine test – Given sample food + Iodine solution → Blue colour solution confirms the presence of starch.

Test for Proteins:

• Biuret test – Given sample food + Aqueous copper sulfate → Violet colouration confirms the presence of Proteins
• Xanthoproteic test – Given sample food + Nitric acid → Yellow colour solution confirms the presence of proteins.
• Millions test – Given sample food + Mercuric sulfate in the presence of sodium nitrite and sulfuric acid → Brick red colour solution confirms the presence of proteins.
• Ninhydrin test – Given sample food + Pyridine solution of ninhydrin → Violet colour solution confirms the presence of proteins.

Test for Oils and Fats:

• Solubility test – Given sample food + Chloroform or alcohol → Miscible with chloroform and immiscible with water the fat presence is confirmed.
• Translucent spot test – Given sample food + rubbed between the folds of filter paper → presence of translucent spot then the presence of fats is confirmed.
• Acrolein test – Given sample food + Potassium bisulfite KHSO 4 → Pungent irritating odor then the presence of fats or oil is confirmed.

Materials Required:

• Molisch’s reagent
• Fehling’s reagent
• Benedict’s reagent
• Tollen’s reagent
• Iodine solution
• Copper sulfate solution
• Sodium hydroxide
• Nitric acid
• Mercuric sulfate
• Sodium nitrite
• Filter paper
• Potassium bisulfate
• Concentrated hydrochloric acid
• Furfural solution
• Test tube holder
• Bunsen burner

Apparatus Setup:

To test the presence of carbohydrates, proteins, fats and oils in the given food sample, first the extract of the given foodstuff should be prepared. Dry the given foodstuff in the mortar with a pestle or by boiling with minimum quantity of water extracting with a small quantity of an organic solvent after grinding the foodstuff.

Some of the examples of preparing extract of food stuff is given below.

• For potatoes – cut to slices and boil with water.
• For butter – test directly
• For grapes – Extract the juice.
• For boiled egg – take the white portion grind and shake with water.

Observation and Inference:

Results and Discussions:

The given food sample contains _________ (carbohydrates/ proteins/ fats).

Precautions:

• Always use minimum quantity of reagents and freshly prepared ones to test the sample food.
• Use droppers to take the reagents from the bottle.
• Use lab aprons and hand gloves during the experiment.

Also, Check  ⇒ Properties of Maltose

Keep visiting BYJU’S to learn more about class 12 CBSE chemistry practicals.

Frequently Asked Questions on Tests of Carbohydrates, Fats and Proteins in Given Food Stuffs

Mention the major types of carbohydrates..

The main types of carbohydrates are monosaccharides, disaccharides and polysaccharides.

Name the bond which holds the monomer units of proteins together?

Peptide bond are the bonds which hold together the monomer units of proteins.

What is called denaturation of proteins?

Denaturation of proteins involves both secondary and tertiary structures being disrupted and potentially destroyed. Because denaturation reactions are not strong enough to break peptide bonds, after a denaturation process, the primary structure (amino acid sequence) remains the same.

Name some of the food source rich in carbohydrates?

Milk, ice cream, yogurt, fruit, whole juice of fruits and grains. Bread, rice, cereal, crackers. Legumes. Beans and other proteins based on plants. Vegetables that are starchy. Maize and potatoes. Sugary candy. Limit it! Soda, sweets, cookies, desserts, etc.

What is the colour of precipitate formed if millon’s reagent is added to food solution having proteins?

Yellow colour precipitate is formed when millon’s reagent is added to food solution having proteins.

Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin!

Select the correct answer and click on the “Finish” button Check your score and answers at the end of the quiz

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Food Chemistry Experiments

Food Chemistry Experiments Index 1. Sugar with Benedict's solution. 2. Protein with Biuret solution. 3. Fat with Sudan III stain. 4. Vitamin C with Vitamin C Reagent . 5. How much sugar is in my soda?

Using Simple 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. You may wish to expand on them and design your own food testing project.

Supplies needed:

• 15 x 125mm test tubes. One per test sample.
• Test tube clamps .
• Test tube rack .
• Mortar and Pestle .
• Small beakers or glass jars .
• Glass marking pen (Sharpie or China marker).
• Nutrient solutions to be tested (made from foods you wish to test for sugar, protein, fat, and vitamin C content).

Food Test 1: Sugar test-Benedict's solution

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 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.
• 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

• 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

• To a test tube, add equal parts of test liquid and water to fill about half full.
• 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

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?

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).

Watch Our How-To Video.

There are many variations of the basic steps outlined above. Let us know what you tested and how your experiment turned out. We'd be delighted to hear from you! Click here and use our Contact Us form.

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EXPERIMENT 8: TESTS FOR NUTRIENTS IN FOODS

Humans consume food in order to obtain energy and be able to do every day work. Different reagents were used to test food samples for their presence of specific nutrients. The objective of this experiment is to test various food samples whether or not they contain mineral matter, fat, vitamin A, cholesterol, carbohydrates and protein, and to determine specific nutrients found in each sample. Fruit juice, raw egg yolk, peanuts tested negative for mineral matter, margarine, raw egg yolk, and peanuts tested positive for the presence of fat, fruit juice, raw egg yolk, peanuts, and cooked rice tested positive for carbohydrates, and raw egg white, peanuts, cooked rice, and dried dilis (anchovy) tested positive for the presence of proteins.

Related Papers

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Abstract Frequently, epidemiologic questionnaires are designed to measure several individual level exposures, including exposure to one or more nutrients. Although most nutrients are contained in a large number of foods, constraints on questionnaire length permit the inclusion of only a subset of these. In this paper, the authors review the two common methods of food selection, and they propose two new methods.

Nutritional Analysis

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Micronutrients and Daily Diet of Young Adults It is important for individuals to consume a varied and balanced diet to meet their nutritional needs and maintain overall health (Lim, 2018). Nutrient adequacy refers to the ability of a person's diet to provide all of the necessary nutrients in the appropriate amounts. Adequate intake of nutrients can vary based on a person's age, sex, weight, and physical activity level (Batal et al., 2021). Consuming an inadequate amount of certain nutrients can lead to deficiencies, which can have negative impacts on health. Of greater significance is the need for a balanced caloric intake throughout the day, which is needed to help regulate energy levels and prevent over- or underconsumption of nutrients. As discussed by Solon-Biet et al. (2015), it is recommended for consumers to spread out calorie intake over the course of the day rather than consume a large portion in one sitting. This can help optimise nutrient absorption and utilisation by the body. The purpose of this report is to evaluate the nutritional content of a 24-hour dietary recall and compare it to appropriate Scientific Advisory Committee on Nutrition Dietary (SACN) Reference Values. The chosen micronutrients for analysis and the reasons for their selection are outlined in the methods section. Nutritics was used as the dietary assessment tool to analyse the macronutrients and three chosen micronutrients in the recall. The discussion particularly focuses on the intake of nutrients in relation to the Scientific Advisory Committee on Nutrition Dietary (SACN) Reference Values and provides recommendations for improving the diet. The adequacy of the recorded diet is also discussed, as is how it could be improved based on the results obtained.

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Summer Research Program for Science Teachers

Barbara Lillien

South Shore High School, Brooklyn

Identifying Food Nutrients

Purpose:     You have just started a job as a food-quality tester.  Your task will be to develop a kit to test foods for sugar, starch, protein and lipids.  The test kit will be used by dietitians who will analyze foods to create nutritional menus for hospital patients.  Your first assignment is to demonstrate proficiency using standard tests for nutrients in foods.

Background:    Substances or compounds that supply your body with energy and the building blocks of macro-molecules are called nutrients.  The food you eat contains nutrition important to your body.   Sugars and starches make up a group of organic compounds called Carbohydrates , which are important in supplying your body with energy.  Some starches provide your body with indigestible fiber, or roughage, which aids digestion.  Organic compounds called proteins are important for growth and repair. Lipids are organic compounds that can supply as much as four times the amount of energy as carbohydrates or proteins.

You can perform qualitative tests to identify the presence of organic compounds in food using Indicators , chemical substances that react in a certain way when a particular substance is present.  Benedict's solution is used to identify the presence of reducing sugars, such as glucose. Lugo's iodine solution is used to identify the presence of starch. Biuret solution is used to identify the presence of protein. Sudan III is used to identify the presence of lipids. A standard is a positive test for a known substance.  Unknown substances can be tested and compared with the standard for positive identification of the substance.

    3. Add 10 drops of Benedict's solution to each test tube. Heat the test tubes in a hot water bath with a temperature rage of 40-50 degrees celsius for five minutes

    4. To perform the Lugol's iodine test, select three clean test tubes. With a wax pencil, label the tops of the test tubes " 1 " " 2 " " 3 "

    5. Add 2 drops of Lugol's iodine solution to each test tube.

    6. To perform the Biuret test, select two clean test tubes. With a wax pencil, label the tops of the test tubes " 1 " " 2 "

    7. Add 3 drops of Buiret solution to each test tube.

    8. To perform the Sudan III test, select two clean test tubes. With a wax pencil, label the tops of the test tubes " 1 " " 2 "

    9. Add 3 drops of Sudan III to each test tube.

    10. Dispose of your materials according to the directions from teacher

    11. Clean up your work area and wash your hands before leaving the lab.

    12. What are the controls in this lab?

    13. Which indicator detects the presence of glucose? ___________ starch? ____________ protein? __________ Lipid? ___________

    14. Describe the color change of the indicators in the presence of glucose, starch, protein, lipids.

    15. Which test tubes contain standards that you could use for comparing tests on unknown substances?

    16. You are asked to analyze and compare a food substance with standards for organic compounds. You observe a positive response with Lugol's iodine solution and Biuret solution.  What can you conclude about this food?

Extensions:

Teaching Standards:

Standards A, B, D, E & F

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Science Projects > Chemistry Projects > Food Chemistry Science Projects + Video  

Food Chemistry Science Projects + Video

Different foods provide different nutrients, like vitamin C, carbohydrates, and lipids. Can you figure out what you’re getting from your favorite food? Use these three simple chemistry tests to sleuth it out. (Note: Adult supervision required when working with chemicals.)

What You Need:

• Food samples: saltine crackers, fruit juices, peanut butter, bread, egg white, applesauce, milk, yogurt, etc.

• Benedict’s solution (glucose indicator)
• Indophenol (vitamin C indicator)
• Brown paper bag (for lipid test)
• Large test tubes
• Plastic lab apron
• Nitrile safety gloves
• Or buy the complete Food Chemistry Experiment kit

Stop the Scurvy – Vitamin C Test

What foods have vitamin C? Do oranges have more than lemons? Do a simple chemistry test to find the answer.

1. Choose several different things to test for vitamin C: tomato juice, orange juice, lemon juice, mango, kiwi, etc. You may also choose a food product that says it has vitamin C added. (If it is a solid, grind it up and mix with water to make a solution.)

2. Make some indophenol solution by combining a small amount (less than 1/8 teaspoon) with 1 cup of water. Stir until it is well mixed.

3. Put 15 drops of indophenol solution into a test tube.

4. Add one of the juices you chose to the indophenol drop by drop. Record how many drops it takes to turn the blue indophenol colorless.

5. Repeat with the other juices and compare the number of drops of each that you added. 3

Vitamin C is a vital nutrient for humans that aids our immune system and helps prevent disease. Many animals can make their own vitamin C, but humans must get it from their diet, which is why the vitamin C content of the food we eat is important. At one time a disease called scurvy was common among sailors, because they had no access to fruits and vegetables at sea. Scurvy is caused by a lack of vitamin C.

Indophenol is an indicator that turns colorless in the presence of vitamin C. The fewer drops of juice you need for the color change, the higher the vitamin C content in the juice. Which fruits had the most vitamin C? Do you think different preserving methods (canning, drying, freezing) has an effect on vitamin C? Do some more tests to find out!

Sugar and Starch – Glucose Test

• Fill two test tubes with an inch of Benedict’s solution each. To one add 15 drops of the saltine-and-water solution, to the other add the saltine-and-saliva solution. (Use two different pipets and label the test tubes so you can tell them apart.)
• Fill a glass with boiling water and then set the test tubes in it and wait for three minutes. Remove the test tubes from the hot water and allow them to cool. Swirl the contents and observe the color of the liquid. Is there a difference between the two?

Glucose is a simple sugar (carbohydrate) that plants produce by the process of photosynthesis. It is the primary source of energy for our body’s cells, and is able to enter our bloodstream quickly to provide energy right away. Without glucose, our bodies wouldn’t function! Plants store extra glucose in a more complex carbohydrate called starch . During digestion, our bodies break the starch back down into glucose for our cells to use as an energy source.

In this project you saw that process in action. Saltine crackers have lots of starch. When you chewed one of the crackers, an enzyme in your saliva, called amylase , started to break the starch down into glucose. Benedict’s solution is a glucose indicator that changes colors based on how much glucose is present. Green, yellow, orange, or red indicates the presence of glucose. The color difference in your two test tubes proves that the chewed-up cracker contained glucose while the other didn’t.

Looking for Lipids – Fat Test

• Cut off the side of a brown paper bag so you have a sheet of brown paper.
• Make solutions of several different foods you want to test for lipids. (You can try milk, peanut butter, yogurt, bread, etc.) Mix 1/2 teaspoon of ground food with 1 teaspoon water.
• Use a permanent marker to divide the brown paper into several sections and label each section with the name of one of the foods, as in the picture on the right.
• Put three drops of each food solution on the paper in its section. Use a clean pipet for each test. Also, test water in one section to show the result with a substance that doesn’t have any lipids.
• Wait a few minutes until the liquid has evaporated. Hold up the paper to the light and look at each spot. The foods that contain lipids will leave a greasy mark that turns the brown paper translucent. Which foods have lipids? Are some of the greasy spots bigger than others?

Lipids are fats and oils, made of molecules that don’t dissolve in water. They are very important for our body functions because they transport vitamins, help form cell walls, and store energy long-term. Eating too much fat can be very unhealthy, but every good diet will contain a moderate amount. How many of the foods you tested contained lipids? Try comparing food that has a “regular” version and a “low-fat” (or “non-fat”) version. Is there a difference between the spots left by skim milk and whole milk?

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Food tests: practical

I can carry out tests for nutrients and some of the substances they are broken down into.

Lesson details

Key learning points.

• Chemical reagents can be used to test for large food molecules including protein, fat, and carbohydrates such as starch.
• Chemical reagents can be used to test for smaller food molecules, such as sugars from the breakdown of starch.
• Interpretation of qualitative food test results.

Common misconception

Confusing the reagents and the substances they test for, or the results of the tests.

Each test is dealt with separately and the positive and negative results are discussed sequentially.

Food test - A food test shows if a specific type of food is present in a sample.

Reagent - A reagent is a chemical used to test for a type of food.

Qualitative - A qualitative test is one that gives an indication of presence, but not an exact figure.

Quantitative - A quantitative test is one that gives a measurable, numerical, value.

pestle & mortar, distilled water, white tile, Iodine & Benedict's solutions, boiling tube water bath

Content guidance

• Risk assessment required - equipment

Supervision

Adult supervision required

This content is © Oak National Academy Limited ( 2024 ), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Starter quiz

6 questions.

Amino acids -  

Glycerol and fatty acids -  

Protease -  

Amino acids

Glycerol and fatty acids

Carbohydrase -  

In a positive test for starch -  

the iodine will turn blue/black in colour.

In a negative test for starch -  

the iodine will stay red/brown in colour.

In a positive test for sugar -  

the Benedict's solution will change colour.

In a negative test for sugar -  

the Benedict's solution will stay blue.

Additional material

BIOLOGY JUNCTION

Test And Quizzes for Biology, Pre-AP, Or AP Biology For Teachers And Students

Food Testing

INTRODUCTION:

Cells are made up of small molecules like water; ions such as sodium and magnesium, and large organic molecules. There are four important types of large organic molecule in living organisms — proteins, carbohydrates (sugars & starches), lipids (fats), and nucleic acids. Proteins, carbohydrates, and fats serve as nutrients in the food that we eat.

In this experiment you will evaluate the nutrient content of unidentified food samples. You will use chemical reagents to test the unknown for specific nutrients. By comparing the color change a reagent produces in the unknown with the change it produces in the known nutrient, you can estimate the amount of that nutrient. Use small samples .

400-ml beaker Hot plate 8 test tubes Test tube rack 4 medicine droppers Glass stirring rod Tongs Several unknown food substances Glucose Cornstarch Non-fat dry milk Lard Distilled water Benedict’s solution Iodine-potassium iodide solution 10% aqueous sodium hydroxide solution 0.5% Copper sulfate solution Sudan III solution

Monosaccharide (simple sugar) test

1. Fill a 400-ml beaker to about 300 ml with water and heat on the hot plate.

Be sure to label all test tubes .

2. Place pea-sized portions of glucose and the unknown substance you are testing in separate test tubes. Add about 2.5 ml of distilled water and 10 drops of Benedict’s solution to each test tube. Mix with a stirring rod, or holding the tube between the thumb and index finger of one hand, thump it with the middle finger of the other hand to mix.

REMEMBER: If you use a stirring rod, wash it after every use, so you won’t contaminate one solution with another.

3. When the water boils, use tongs to place the test tubes in the water bath. Leave the test tubes in the water bath for 10 minutes .

Do not let the water bath boil hard. Control the boiling by turning the hot plate on and off as needed.

4. Remove the test tubes with tongs and place the tubes in a test tube rack. Unplug the hot plate to cool. When the tubes cool, an orange or red precipitate will form if large amounts of glucose are present. Small amounts of glucose will form a yellow or green precipitate. Record your observations in the DATA TABLE .

Polysaccharide complex sugar) test

5. Place cornstarch in a clean test tube and some of the unknown substance in another. Use a clean dropper to add 10 drops of iodine-potassium iodide solution to each test tube. Observe the results and record in the DATA TABLE .

Protein test

6. Place non-fat dry milk in a clean test tube and some of the unknown in another. With a clean dropper slowly add an amount of sodium hydroxide solution about equal to the amount of the milk sample, and mix carefully. Then add 10 drops of copper sulfate solution one drop at a time. Mix gently between drops. Observe the results and record in the DATA TABLE .

7. Repeat step 6 with the unknown substance.

8. Place a small piece of lard in a clean test tube and some of the unknown in another. Use a clean dropper to add 10 drops of Sudan III solution to each test tube. Mix well, observe and record your results in the DATA TABLE .

DATA TABLE:

CONCLUSIONS:

Question 1 . What is the main nutrient in the unknown?

Question 2. What are the controls in this investigation?

Practical Biology

A collection of experiments that demonstrate biological concepts and processes.

Observing earthworm locomotion

Practical Work for Learning

Published experiments

Quantitative food tests.

Qualitative food tests will be familiar to teachers. There are some protocols available for making estimates of the quantity of different foodstuffs (protein, starch or reducing sugar) in certain foodstuffs.

Experiments

• Quantitative food test: protein content of powdered milk

• 7 Food Science Experiments to Promote Healthy Eating
• After School Activities

Share This Activity

September is Childhood Obesity Awareness Month, and it’s an ideal time to teach students about the benefits of healthy eating.

The percentage of children with obesity has more than tripled over the past 40 years. In fact, about one in five school-aged children (ages 6–19) are considered obese, according to the Centers for Disease Control and Prevention (CDC).

The Effects of Childhood Obesity

Children with obesity are more likely to have hypertension, high cholesterol and asthma, among other health conditions. They also have an increased risk of developing serious health problems as adults, like heart disease or type 2 diabetes. Childhood obesity can also have emotional consequences, such as low self-esteem, anxiety and depression.

Obesity doesn’t only affect children’s physical and mental health; it also has an adverse effect on their academic performance. Past research found that obese students, especially girls, tend to have lower test scores than their peers, are more likely to be held back a grade and are less likely to go on to college.

Food Science Experiments for Kids

While many factors contribute to childhood obesity, like genetics, metabolism and lack of exercise, adopting healthy eating habits can be effective at preventing the condition. The following food science experiments explore concepts like calories and fat to encourage students to make healthier food choices:

Fatty Foods

Objective: Learn a simple way to test the amount of fat in different foods.

Overview: Students will use the paper bag test to compare the amount of fat in apples, butter, potato chips and other foods. The experiment also provides an opportunity for students to learn the difference between unsaturated (good) and saturated (bad) fat, plus the effects of eating too much “bad” fat.

Source: Children’s Museum of Houston

Testing for Glucose and Starch

Objective: Use simple tests to determine the presence of glucose and starch in everyday foods.

Overview: All foods contain chemicals, and glucose and starch are among the most common ones. Before starting the experiment, use this article to explain the difference between starch and glucose, and their effects on the body. Then, conduct this experiment to find these chemicals in foods like marshmallows, peanut butter and applesauce.

Source: Discovery Education

Water Content in Fruits and Vegetables

Objective: Understand the nutritional value of the water content of fruits and vegetables; Encourage students to think about the properties of healthy foods.

Overview: Many fruits and vegetables contain water, but it doesn’t always mean they are filled with key vitamins and minerals. For this experiment, students will measure the water content of the fruits and vegetables, and compare the results to the food’s nutrient value. At the end of the experiment, they should know whether or not each food’s water content is associated with its nutritional value.

Source: education.com

How Greasy Are Your Potato Chips?

Objective: Investigate how much fat is in typical potato chips and potato crisps.

Overview: Potato chips is one of the most popular snacks, but some varieties contain an unhealthy amount of fat. In this experiment, students will look at four different kinds of chips and crisps to test how much fat each product contains. Be sure to explain how our body uses fat and the effects of consuming too much of it.

Source: Science Buddies

Energy Content of Food

Objective: Build a simple tool to determine the amount of calories in certain foods.

Overview: Designed for middle school students, this experiment explores concepts like calories, the caloric value of different foods and the amount of calories children should consume in one day. Students will build a simple calorimeter to measure the amount of heat given off when food is burned to determine the caloric value of bread, cheese and other food samples. This experiment requires students to burn the food using matches, so adult supervision is a must!

Demystifying the Sugar Buzz

Objective: Learn the different effects that sugar and starch have on the body.

Overview: Sugar enters the bloodstream faster than starch (found in foods like flour, potatoes and beans), causing a “sugar buzz.” This experiment will demonstrate how fast, or slow, sugar and starch pass into artificial blood.

Source: howstuffworks

Upcycling Food Scraps

Objective: Find low-cost, sustainable ways to grow and eat organic foods.

Overview: Buying healthy, or organic, produce can be expensive. This infographic from Whole Foods provides steps on using food scraps to easily regrow food. To demonstrate food upcycling, choose one of the foods listed in the infographic - like green onions, celery or sweet potatoes - and create a food garden in your classroom.

Source: Pinterest

Healthy eating is an effective way to prevent childhood obesity. These food science experiments are designed to encourage students to think about the foods they eat and how they affect their body. You can also check out our Healthy Choices Play Food Set to further help students practice making healthy food choices. 

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Lesson Plan: Food Tests

This lesson plan includes the objectives and prerequisites of the lesson teaching students how to describe chemical tests that are used to determine the type of nutrients present in food.

Students will be able to

• state that food tests are used to identify nutrients that are in food products,
• describe how solid samples are prepared to carry out food tests,
• describe the tests for starch, sugar, lipids, and proteins as iodine, Benedict’s reagent, ethanol/emulsion, and Biuret respectively,
• describe the expected observation if these tests are positive,
• understand how to carry out laboratory work safely.

Prerequisites

Students should already be familiar with

• the major types of nutrients found in food.

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01. Food Tests

Test for reducing sugars

• 00:51 What is the colour of the mixture at the start?
• 01:06 What do you observe in the tube after heating for 5 minutes?

Test for non-reducing sugars

• 01:10 What is the colour of the mixture at the start?
• 01:26 What do you observe in the tube after heating for 5 minutes?
• 01:28 Why do you add dilute hydrochloric acid to the non-reducing sugar and heat it?
• 01:44 Why do you then add dilute sodium hydroxide or sodium bicarbonate?
• 01:51 What do you observe?
• 01:58 Can you explain why the Benedict’s test was negative at first, and then positive after adding acid, heating and adding alkali?

Test for protein

• 02:06 What colour is Biuret reagent at the start?
• 02:23 What colour is the solution after adding Biuret reagent?

Test for starch

• 02:26 What colour is iodine-potassium iodide solution at the start?
• 02:35 What colour is iodine-potassium iodide solution in the presence of starch?

Test for fats and oils

• 02:46 What do you observe where the alcohol and oil meet?

5 boiling tubes

2 test tubes

3 dropping pipettes

Benedict's reagent

dilute hydrochloric acid (0.5 moldm -3 )

dilute sodium hydroxide solution/sodium bicarbonate

Biuret reagent

iodine-potassium iodide solution

absolute alcohol

glucose solution

sucrose solution

albumen solution

starch solution

Food Tests ( CIE IGCSE Biology )

Revision note.

Last updated

Food tests in biology

Food test for glucose (a reducing sugar).

• Add Benedict's solution into sample solution in test tube
• Heat at 60 - 70 °c in water bath for 5 minutes
• Take test tube out of water bath and observe the colour
• A positive test will show a colour change from blue to orange or brick red  

Use this image

The Benedict's test for glucose

 Food test for starch

• We can use iodine to test for the presence or absence of starch in a food sample.

The iodine test for starch

• Add drops of iodine solution to the food sample
• A positive test will show a colour change from orange-brown to blue-black

Testing a potato to prove the presence of starch

Food test for protein

• Add drops of Biuret solution to the food sample
• A positive test will show a colour change from blue to violet / purple

The Biuret test for protein  

Food test for lipids

• Food sample is mixed with 2cm 3 of ethanol and shaken
• The ethanol is added to an equal volume of cold water

The ethanol test for lipids

Food test for vitamin C

• Add 1cm 3 of DCPIP solution to a test tube
• Add a small amount of food sample (as a solution)
• A positive test will show the blue colour of the dye disappearing

The DCPIP test for vitamin C

When describing food tests in exam answers, make sure you give the starting colour of the solution and the colour it changes to for a positive result.

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NOTIFICATIONS

Using laboratory models to test the effects of foods.

• + Create new collection

One way of testing food compounds is by using laboratory models.

As part of the nutrigenomics project, researchers are trying to identify food compounds that are likely to be especially helpful (or harmful) for people with particular genetic combinations.

One of the ways they did this was by using laboratory models.

Why are laboratory models needed?

It would be inappropriate to directly test the effects of different food compounds using people. There are several reasons for this.

Firstly, it would be difficult to monitor the effects of only the food compounds, and not any other environmental factors (the person would have to live in a controlled environment for the duration of the experiment).

Secondly, all research needs to be repeatable. Because the way we respond to food is controlled partly by our genes, researchers would need to find several people who had exactly the same genotype . This would be impossible, as only identical twins have the same genes.

Thirdly, there are thousands of food compounds. You would either need a huge number of willing participants (all with the same genotype) to be able to test all the foods, or you would need to involve each person in a very long-term study (to test all the food compounds in isolation).

Then there are the ethical issues. No-one would agree to participate in the experiment unless they were assured that the tests were unlikely to cause significant harm. The researchers would not be able to guarantee this unless they already knew a lot about the responses that the food compounds are most likely to cause.

What are cell lines?

One way that the interactions between food and genes can be studied in a laboratory is by using a cell line. A cell line is a group of cells that grow and replicate continuously in vitro in a laboratory.

Cells in a cell line are immortal . They will keep growing for as long as they have sufficient nutrients. However, they will always only ever be individual cells. They will never be able to grow to become a whole organism.

Why are cell lines useful?

Cell lines are useful for research because every cell in a cell line has identical genes (all the cells originate from one cell). This means that they should all respond in exactly the same way to a particular treatment, allowing for repeatability.

In addition, different groups of cells from a cell line can be used for testing different molecules.

In the case of nutrigenomics , the effects of food compounds are tested. By using a cell line, a huge number of different food compounds can be tested in a relatively short time.

How are cell lines used in nutrigenomics research?

In the nutrigenomics project, cell lines will be used to test the effects of thousands of different food compounds. The cell lines need to behave as closely as possible to cells from a person who has a particular genetic predisposition.

The New Zealand researchers are first studying the effects of different foods on people who have inflammatory bowel disease (IBD).

The cell lines that are used to test the foods need to behave as much as possible like cells from someone who has IBD.

Genetic engineering techniques are used to insert copies of gene variants associated with IBD into the cells.

Remember, though, that these cells will never be able to be anything other than individual cells. They cannot grow into an organism.

The need for reporter genes

Cells are tiny and can usually only be seen with a microscope. It is even more difficult to tell what is going on inside cells. The researchers need to have a way of measuring the effects that the food compounds have on cells.

A reporter gene is inserted into the cells. The reporter gene is selected because of its ability to produce a reaction that researchers can measure. Often the luciferase gene is used. This is a gene that is found in fireflies. It causes luminescence, or glowing, when it is activated. Researchers can tell the effect that a food compound has on a cell by whether or not the cells glow. The amount of glowing is measured by a machine called a luminometer.

Limitations of cell lines

A cell line will not behave exactly in the same way as cells that are part of a whole body. However, the results from the cell line tests allow researchers to make better predictions about the effects food compounds might have on people with particular genes.

Other laboratory models

Laboratory animals can also provide a useful way of testing the effects of foods. Rats and mice are particularly useful because they reproduce very quickly.

Planned breeding programmes can ensure that the mice have particular genetic characteristics (something that can’t be done with human participants). Inbred strains allow for replication of experiments.

Environmental factors can also be easily controlled (compared with controlling the environment of a human participant).

All research carried out using animals needs to be done according to strict ethical guidelines. This is to protect the welfare of the animals.

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