How to Test Food for Starch?

Introduction: (Initial Observation)

We have heard about food starch, laundry starch, starch glue and it seems that starch has many industrial applications. We also know that many foods and fruits contain a large amount of starch that is usually a concern for those who care about their diet. This concern is because starch molecules will break down to sugar molecules in our body. But what is starch exactly and how can we identify it?

How can we test to see which foods contain starch and which one don’t?

Information Gathering:

Find out about starch and how it can be tested. Read books, magazines or ask professionals who might know in order to learn about the sources of starch. Keep track of where you got your information from.

Starch is a carbohydrate! But what is a carbohydrate?

There are three groups of substances that are called carbohydrate. First group are monosaccharides that are simple sugar found in many fruits with a general formula of C6H12O6. The second group is disaccharides such as sucrose (table sugar) with a general formula of C12H22O11. And finally the last group is called Polysaccharides such as starch and cellulose. So simple sugar found in apple juice, table sugar, starch and cellulose (wood, cotton) are all carbohydrates. Starch molecule is a very long chain of sugar molecules. Such a long chain of identical molecules is called a polymer. So starch and wood are both polymers made up of small units and each unit in this case is a sugar molecule.

All carbohydrates are made by plants. When plants grow, they get carbon dioxide from the air and water from the ground and use the energy from the sun to produce carbohydrates. Carbohydrates form the body of the plants.

Problem/ Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

Starch in food is hazardous for people with disease such as diabetes. In order to avoid starch, patients need to know which foods or fruits contain starch. In this project you will identify some of the fruits, vegetables and foods that contain large amounts of starch.

Some of the questions related to starch are:

1. 1. What foods contain starch?
   2. What vegetables contain starch?
   3. What industrial products contains starch (Paper, Envelop, Stamp, Glue, Fabric)
   4. How do starch molecules break down to sugar molecules?
   5. What papers contain starch?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

This is a sample of how you may define variables:

The Independent variable (also known as manipulated variable) is the type of food or fruit selected for starch test. (In other words we choose different variations of food to test).

The dependent variable (also known as responding variable) is Starch presence (Yes, No). (In other words presence of starch in food depends on the type of food.)

Constants are the type and concentration of the starch indicator solution.

Controlled variables are light, temperature and other environmental conditions that may possibly affect the test results. (Test all samples at the same time and in the same room).

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

Some sample hypothesis are here:

• • I think beans contain starch
  • I think grains contain starch
  • I think grape does not contain starch because it is sweet, so all it’s starch is broken down to sugar.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Get Iodine solution

To test a food or other material for presence of starch, you need an Iodine solution. Iodine solution may be available at your local pharmacy in the form of Iodine Tincture. Iodine tincture is an Iodine solution that also contains alcohol.
Iodine tincture is a topical antiseptic for use on superficial cuts, insect bits and bruises. May be diluted with water. Germicide providing germicidal activity against bacteria, fungi, viruses and protozoan. Protective agent for painting baby calf and pig navels following birth.

If you have Iodine tincture, skip the next two paragraphs for preparing Iodine solution and recipe.

Preparing the Test Solution

If you frequently need to use Iodine Solution, it is better to prepare it fresh. Iodine solution is sensitive to light and if you want to keep it for a long time, it should be stored in a dark container. A dark-colored bottle or a clear bottle wrapped in aluminum foil will serve the purpose. Chemicals needed for this test are potassium iodide and iodine crystals. A pharmacist or a chemist can use the following recipe to make up the iodine solution.

Recipe

1. Dissolve 8.8 grams of potassium iodide in about 30 ml of warm water. Gently stir the solution until potassium iodide is properly dissolved.
2. Add 2.2 grams of iodine crystals. Shake the mixture until the crystals are thoroughly dissolved.
3. Dilute this mixture with water to make 1.0 liter of test solution. Mix them well.

Experiment 1:

Testing Food for starch presence

Introduction

All living things need energy. Plants get their energy from the sun and store it in the form of carbohydrates. All animals need carbohydrates for energy and proteins for the repair of body cells. A diet that contains all the chemicals vital to life is a Balanced Diet.
Before food can be used by animals, it must be broken down or digested. When digested, proteins provide amino acids, carbohydrates provide sugars, and fats provide fatty acids. You will test selected foodstuffs for starch, sugar, and/or protein, and summarize your observations.

Theory

Starch, a carbohydrate, can be identified by a positive iodine test. A few drops of iodine solution are added to a raw or boiled sample of the substance suspected of containing starch. If starch is present, the substance will turn blue-black in the area where the iodine solution touches it. Substances with very small amounts of starch will turn faint blue or greenish instead of blue-black. Many biodegradable materials have high starch content. These materials can be identified with the iodine test.

Like starch, sugars are carbohydrates. They are also saccharides a class of chemical compounds. The term saccharide derives from the Greek sakkharon, meaning sweet. The saccharides range from simple compounds, monosaccharides, to large complex molecules, polysaccharides. A monosaccharide is a simple sugar; examples are glucose and fructose. A disaccharide is a sugar that is composed of two simple sugars. Examples are sucrose or table sugar, lactose or milk sugar, and maltose or malt sugar. Polysaccharides are complex sugars comprised of many monosaccharides. Starch and cellulose are polysaccharides.

Procedure

TESTING FOR STARCH USING IODINE SOLUTION

1. Measure out one-fourth teaspoon of flour and place it in a petri dish. Add three tablespoons water and stir. Add three drops of iodine solution and record your observations. This color change indicates the presence of starch.
2. On a paper plate, place small samples of the following items.
   – A piece of notebook paper
   – A piece of cheese
   – A potato slice
   – A piece of bread and/or cracker
   – Granulated table sugar (sucrose)
   – An apple slice
   – A piece of pasta
3. Place one drop of iodine solution on each sample. Record your results in a data table.
4. Prepare a test sample of cornstarch?
5. Test other foodstuffs for starch and record your observations in a separate data table.

Challenge Questions

STARCH

1. For which of your samples were the results similar to the results obtained with flour?

2. Which of your samples contained starch?

3. Are the results of the iodine test for cornstarch positive or negative?

Note: One drop of iodine solution on a food sample can show if starch is present or not. I have tested foods such as spaghetti, cooked rice, cooked beans and chicken broccoli soup in this way. Presence of starch will change the color of iodine to dark blue. This test will not work on foods such as black beans that have a dark color.

Need a control experiment?

If you are doing your tests in different times, then someone may doubt your results and suggest that possibly another factor may have caused the blue color, not the starch. That is why every time you test a fruit, you also run a control experiment. In your control experiment you place a drop of starch indicator on a ceramic or porcelain plate just to make sure that it does not turn to blue by itself.

Experiment 2:

STARCH HYDROLYSIS BY AMYLASE

(For higher grades only)

Introduction

Starchy substances constitute the major part of the human diet for most of the people in the world, as well as many other animals. They are synthesized naturally in a variety of plants. Some plant examples with high starch content are corn, potato, rice, sorghum, wheat, and cassava. It is no surprise that all of these are part of what we consume to derive carbohydrates. Starch molecules are glucose polymers linked together with special bonds. In order to make use of the carbon and energy stored in starch, the human digestive system, with the help of the enzyme amylases, must first break down the polymer to smaller sugars, which is eventually converted to the individual basic glucose units.

Starch is generally insoluble in water at room temperature. Because of this, starch in nature is stored in cells as small granules, which can be seen under a microscope. Starch granules are quite resistant to penetration by both water and hydrolytic enzymes. However, when an aqueous suspension of starch is heated, the water is absorbed, and the starch granules swell. This process is commonly called gelatinization because the solution formed has a gelatinous, highly viscous consistency. The same process has long been employed to thicken broth in food preparation.

The enzyme that will break the starch molecules down to sugar molecules is called alpha-amylase. Since a wide variety of organisms, including humans, can digest starch, alpha-amylase is obviously widely synthesized in nature. For example, human saliva and pancreatic secretion contain a large amount of alpha-amylase for starch digestion. The specificity of the bond attacked by alpha-amylases depends on the sources of the enzymes. Currently, variety of alpha-amylases is commercially produced through microbial fermentation. But for our experiment we will use human saliva as a source of amylase enzyme.

Procedures

Because there is a variety of physical conditions that may affect the outcome of this experiment, we make enough starch solution for multiple tests.

Prepare a 20 g/l starch solution.

1. 1. Mix 2 g of soluble potato starch in approx. 5 ml of cold water.
   2. While stirring, add the slurry to approx. 90 ml of gently boiling water in a large cup.
   3. Mix well and cool the gelatinized starch solution to room temperature.
   4. Put a few drops of the starch solution on a glass plate or petri dish. Add 1 drop of the iodine reagent and see that a deep blue color is developed. The blue color indicates the presence of starch in the solution.

Test the effect of Amylase Enzyme

1. Collect enough Saliva as a source of Amylase enzyme.
2. Prepare three test tubes and number them from 1 to 3
3. Add 1 milliliter saliva to the test tubes 1 and 2
4. Add 5 milliliter starch solution to each test tube
5. Put the test tube number one in a cup of warm water so it will stay warm and keep the tubes number 2 and 3 at the room temperature.
6. After 10 minutes add three drops of Iodine solution to each test tube.
7. Record your observation

Repeat this experiment with the same amounts, just change the time and record the results in a table.

After certain amount of time, starch test on test tubes number 1 and 2 will result negative. That indicates that all starch molecules are broken down to sugar molecules.

Experiment 3:

Identify Counterfeit Bills

Most stores test large bills with a special pen, to see if they are counterfeit, Instead, you can put a drop of iodine solution on the bill to be sure that it was good. To see why, you will need:

• •    Tincture of iodine (Iodine Solution)
  •    Paper
  •    A dollar bill
  •    Bread or a cracker

Warning! Iodine is poisonous and will stain skin and clothing. Also, some people are allergic to iodine. Be safe and careful.

Use a transfer pipette or a toothpick to put a tiny bit of iodine on a piece of white paper. Notice that the paper turns black. Put a drop of iodine on a piece of bread or cracker and it will also turn black. This is an indicator test. Iodine turns black when it comes in contact with starch. Most paper contains starch and will turn black with iodine.

Now put a drop of iodine on a dollar bill. It stays a brownish color. The special paper used from printing U.S. money does not contain starch, which is one of way that you can spot a counterfeit bill.

Try testing small pieces of different fruits and vegetables, to see which ones contain starch. Be sure to throw away the things you test, to be sure that no one accidentally eats any of the iodine. You might also try testing different kinds of paper, to see if you can find any others that are starch-free. Any of you that are outside the U.S., can check to see if the bills from other countries are starch-free too.

If you are doing this experiment as a science project you may need to record your results in a table.

Experiment 4:

Apple Maturity on Your Farm

The single best measure of determining apple maturity for storing apples is the starch pattern that develops in the fruit. Fruit firmness, soluble solids (sugar) levels, and skin color are all important factors in determining the eating quality and/or salability of apples. When the apple goes toward maturity, the starch molecules break down to sugar molecules.

A solution of iodine and potassium iodide (Iodine Solution) is used to make the starch turn black, and this pattern is the basis for the test. Over the years charts have been developed for many varieties of apple.

Predicting Harvest Date Windows for Apples Full-color plates show how to use and interpret the starch-iodine test for determining maturity and the best harvest dates for quality; especially important for apples going into storage.

Warning

Iodine is a very poisonous chemical. The iodine solution should be properly labeled and kept away from children and pets. Apples used in the test should not be fed to any animals or used in composting. In case of ingestion of either iodine or iodine-treated apples, induce vomiting and consult a physician immediately.

Materials and Equipment:

Some of the material or equipment that you may use in your experiment are:

1. Iodine solution or Iodine Tincture
2. Test tubes or similar clear container
3. Test tube brush (size 11-12) for washing your test tubes after use.
4. Cornstarch Peanuts for test (These are used as packing material)
5. Corn Starch
6. Two Petri dishes or similar flat dish
7. Transfer pipettes or droppers
8. Samples of fruits and other food items

Where to buy iodine solution?

In some areas you can find all you need locally. If you prefer to purchase online, you may try the following websites:

www.ChemicalStore.com sell iodine solution in small packaging

www.MiniScience.com sell iodine solution, petri dishes, test tubes and other science supplies. There is also a starch test kit available at MiniScience.com.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

No calculations is required for this project.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

List of References