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Test fruits or fruit juices for starch

Test fruits or fruit juices for starch

Introduction: (Initial Observation)

While learning about plant growth and photosynthesis, we learned that green plants use the energy from the sunlight, water from the ground and carbon dioxide gas from the air to make starch. Starch is the reservoir of food for plants.
In this project you will test the presence of starch in edible plant parts, specially fruits. For better results, you must make your own juice. Processed juice sold in stores may have gone through stages to lose their starch content.

Try green fruits as well as ripe fruits. Also try corn, potato, carrot, broccoli, cantaloupe, cucumber, eggplant. Do not restrict yourself to the sweet fruit juices that you usually drink. Most such juice have no starch at all.

By selecting variations of green and ripe plants, you can also determine if the amount of starch changes as the fruit ripen.

This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

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.

Find out about starch and how it is made. Read books, magazines or ask professionals who might know in order to learn about the factors affecting the production of starch. Keep track of where you got your information from.

The picture on the right is from an starch test experiment on a leaf. Parts of the leaf with starch turned black. Do you see any relation between green chlorophyll and the production of starch?

How to make 1% Cornstarch solution?

  1. Measure 10 grams of starch and dissolve it in about 100ml of water. Mix it to get a milky solution.
  2. In a glass beaker or cooking pot that is graduated or marked for one liter, heat up about 600 ml water to boil.
  3. Slowly add the milky solution that you have made to the hot water and continue stirring until the solution is clear (as much as possible).
  4. Add water to the solution to bring it up to one liter. That will make a 1% solution of starch.

Estimate all the measurements if you don’t have scales or measuring cups. A 1% solution of starch is a solution that contains one part starch and 99 parts of water (by weight). Starch does not dissolve in hot water. That is why you initially mix it with cold water.

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. 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.

The type of food that we test is a manipulated or independent variable for our investigation. (In other words we choose different variations of food to test). The dependent variable is Starch presence (Yes, No).

In other words presence of starch in food depends on the type of food.


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.

Following are some samples of Hypothesis for some sample Questions.

Q: What foods contain starch?

H: Among the carrot, broccoli and corn, the corn contains starch but broccoli and carrot don’t. My hypothesis is based on my observation of products in grocery stores. I have seen packs of corn starch but I have not seen packs of broccoli starch or carrot starch.

Q: What papers contain starch?

H: Among copy paper, currency paper, and newspaper paper, copy paper contains starch. My hypothesis is based on my observation of the color of starch that is white, so gray or brown papers are most likely starch free papers.

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.”

Experiment 1:

Testing Fruit juices for presence of starch


Starch is a substance produced by green plants during the process of photosynthesis. In our body, starch will be converted to sugar which is a high energy food.

Starch can be identified using iodine solution. A solution of iodine added to starch will form a dark blue compound. This method is used to identify starch.

All plants have some type of fruit. Certain fruits are edible and are used as food. Depending on the type of fruit, we may be able to eat it raw or not. For example Cucumber is fruit that we eat it raw while egg plant is a fruit that we eat after cooking.

In this experiment we will test all fruits in raw form. Cooking may modify the composition of fruit material or change the amount of starch.

To test a fruit, cut it in peaces, filter the extract and test the clear extract/ juice. Do not try berries or fruits with a deep color. Fruit color can prevent observation and determination of test results. Discoloration of fruits is not possible with simple methods.

The reason that we will test both immature and well developed fruits is that other reports have shown that fruits gradually lose their starch as they mature. A ripe fruit may have no starch at all.


  1. Collect samples of fresh fruits that you want to test.
  2. Wash the fruits and peel the skin off only if you have to.
  3. Use a juicer to make the juice. If you don’t have a juicer, first use a grinder to shred the fruit; this will create some juice. Additional juice may be obtained by squeezing the shredded fruit in a clean cotton cloth. Make sure the juice is as clear as possible.
  4. Transfer the extracted juice to a test tube and label the tube with the name and type of the fruit. For example you may use labels such as “ripe apple” or “unripe apple”. For best results, all the test tubes must have the same amount of juice. About 5 milliliter of juice in each tube is a good amount.
  5. In a separate cup make a 1% solution of corn starch. Get two test tubes and to each test tube add 5 milliliter of the starch solution you just made. Label one tube as starch; label the other tube as control.
  6. Do nothing with the control tube; but, to all other tubes add five drops of iodine solution each.
  7. Swirl each tube and look for any color change to blue or black.Change of color to blue, dark blue or black indicate the presence of starch.Record the results in your results table. If your fruit juice is yellow, then the blue color may appear as green.

This is a sample results table:

Fruit name No Color Change Color change to light blue Color change to dark blue Color change to black
Ripe apple
Unripe apple
Ripe pear
Unripe Pear
Ripe Corn
Unripe Corn
Ripe Cantaloupe
Unripe Cantaloupe
Ripe Banana
Unripe Banana
Starch solution

Place only one X in each row (for each sample) according to your observation.


  1. The actual number of rows in your results table depend on the number of fruits you choose to test.
  2. No color change means no starch.
  3. 5 milliliter is about one spoonful liquid.
  4. Warning: Be sure to throw away the things you test, to be sure that no one accidentally eats any of the iodine.

Experiment 2:

Testing fruits for starch

Introduction: Often farmers and producers of fruits need to test the fruit for presence of starch. Unripe fruits often have a high amount of starch, so they don’t taste good and they are not acceptable to the market. Farmers check the amount of starch in a few samples of fruits and then use the results to estimate when their produce will be ready for market. This is important because farmers need to plan in advance for their harvest time. They need to find customers, rent trucks, hire workers and reserve cold storage space for their produce. In this experiment we will test the fruits the same way as the farmers do. This test is very popular for apple. The following is a chart for testing apple for starch.

Farmers use a chart like this to test the fruit maturity, ripening and determining harvest date. To get the best results for this experiment, you must have access to unripe fruits. (Fruits lose their starch as they ripen.)


Use a shallow glass pan. Pour some iodine solution into this pan to a depth of 5-8 mm.
Cut each fruit sample in half. Soak the cut surface of the fruit in the iodine solution for one minute.
Remove the fruit from the test solution and place them cut surface up to drain.
Score each fruit by the ratio of the cut surface changed to blue or black. For example score 0 if you have no blue or black. Score 10 if all the cut surface is blue or black. Score 5 if about half of the cut surface is changed to blue or black.
Note: This experiment is great if you have access to an apple tree or any other tree and can get samples and repeat this test as the fruits grow towards maturity. By recording the test dates you can determine how long does it take for the fruit to lose all its starch.

Warning: Be sure to throw away the things you test, to be sure that no one accidentally eats any of the iodine.

More information (for higher grades):

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.


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.

Starch is a polymer of glucose, also known as dextrose. The standard test for the presence of starch in juice is the iodine test. In the presence of starch, iodine will form a characteristic blue-violet color. A negative test by iodine indicates that all of the starch has been reduced to a chain length of less than nine to twelve glucose units, a size sufficiently reduced that it will not produce post-bottling hazes.
The starch test consists of adding a drop of I 2 KI (iodine solution) to the sample
to be tested. If the iodine retains its yellow-brown color, starch is absent …

Experiment 3:

Identify Counterfeit Bills


Most stores test large bills with a special pen, to see if they are counterfeit. The ink in these pens is really the iodine solution; so, all they are doing is testing the paper for starch. The fact is that all papers used for printing or copying contain starch; but, the paper used in making currency has no starch.

You can do the same test using the iodine solution. Use a copy machine to make a copy of a dollar bill. Then test both the dollar bill and the copy that you made by a drop of iodine solution.

Material you need:

  • 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.

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.

Materials and Equipment:

Get Iodine solution

The most important substance that you need for your experiments is iodine solution.

Iodine solution may be purchased online or from a local pharmacy.
Following are two of the online stores you may order iodine solution:

http://shop.MiniScience.com Product code: IODINE_S29

http://www.ChemicalStore.com Product Code: IODINE_S29

If you are ordering online, don’t wait until the last minute. Shipping charges are much less when you have enough time for your order to arrive.

Other possible options for 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.


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.

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


If you do any calculations in relation to your experiments, write your calculations in this section of your report.

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.


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.


Visit your local library and find books related to photosynthesis and starch. Look for sections that discuss starch test. List such books as your references.
Following are some online references:

Evaluating Maturity of Empire, Idared and Spartan Apples by starch test.

Test foods for starch

Additional Starch Experiments:

http://faculty.ntcc.edu/mhearron/photosynthesis.htm Photosynthesis

http://www.austincc.edu/microbugz/40starch.html Starch Hydrolysis test