Starch Test Kit
This Starch Test Science Kit, introduces some of the sources and applications of starch.
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.
Depending on your question,
you can have a different hypothesis.
Food for starch presence
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.
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.
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. How would you prepare a test sample of cornstarch?
5. Test other foodstuffs for starch and record your observations in a separate data table.
Post-Lab Challenge Questions
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?
HYDROLYSIS BY AMYLASE
(For grades 10-12)
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.
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.
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.
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
Conclusion: In your conclusion write the time it takes for the starch to fully hydrolyze and convert to sugar.
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)
· 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.
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.
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.
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.
Questions & Answers:
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.