Searching for Starch
FOOD EXPERIMENT: STARCH
______________________________________________________________________________
The following experiment is designed to supplement activities in already
existing food and nutrition projects. First read the section "Caution-Be
Science Wise" and then help 4-H members work through the experiment.
CAUTION - BE SCIENCE WISE!
Before you begin any science experiment, you should always follow these basic
rules:
1. Be sure to read ALL directions before starting the experiments.
2. In many experiments, a "control" is used. The control is the standard
against which you compare the experimental food.
3. When doing the experiments, keep everything the same as the control except
for the one thing the directions say to change. Use the same size pans,
the same type of bowls and the same mixing speeds. Be sure that just ONE
thing changes each time.
4. Be sure to label each food when conducting these experiments. Use a piece
of masking tape, a marking pencil, a crayon or anything that will help you
remember which food is which. In some experiments, you'll have no trouble
telling the foods apart. In others, the foods may look the same.
5. The experimental food is not meant to be perfect. Since you are purposely
doing something wrong, you can't expect it to be perfect! So it's all
right when something turns out "bad." That's what is SUPPOSED to happen.
6. Not all experiments in food science yield products that can be eaten.
NEVER SAMPLE PRODUCTS IN AN EXPERIMENT UNLESS YOUR LEADER SAYS THEY ARE
SAFE TO EAT.
7. Records are an important part of any scientific project. You should write
down what happens in each experiment. Experiments may not turn out exactly
the same every time. Recording your results will help you and others who
may try to repeat your experiment.
SEARCHING FOR STARCH
INTRODUCTION
Many different foods (including GRAIN foods) contain the carbohydrate called
starch. To see if foods have starch, you can test them by using iodine. Be
careful in handling iodine. It can stain clothing, equipment and skin, and IT
IS POISONOUS. DO NOT put iodine in your mouth and DO NOT eat any tested
foods.
INGREDIENTS
1 tablespoon milk
1 egg
1/2 slice bread
1 slice raw potato
1 tablespoon flour, cornstarch or dry tapioca
1 slice cucumber
1 teaspoon sugar
1 slice unripe (green) banana
EQUIPMENT
Newspapers
Cutting board
Knife
Measuring spoons
Iodine (not decolorized iodine)
Medicine dropper
3 paper plates
2 disposable plastic cups
PROCEDURE
1. Place several layers of newspaper on a table. Be sure to do this
experiment on the newspapers since iodine will stain a table.
2. Place the milk in one cup and the egg in the other cup. Put the other
foods to be tested on paper plates. (You can put more than one food on a
plate.) Remember to put the plates on the newspaper.
3. With the medicine dropper, put a few drops of iodine on each food to be
tested. If starch is present, the iodine will change from reddish-brown
to bluish-black. REMEMBER, DON'T TASTE ANY OF THE FOODS TESTED!
4. Record what you find as you test each food.
______________________________________________________________________________
Food Color Is starch present?
Yes No
______________________________________________________________________________
Milk
______________________________________________________________________________
Egg
______________________________________________________________________________
Bread
______________________________________________________________________________
Potato
______________________________________________________________________________
Flour, cornstarch or tapioca
______________________________________________________________________________
Cucumber
______________________________________________________________________________
Sugar
______________________________________________________________________________
Banana (green)
______________________________________________________________________________
5. Put the iodine away and wash your hands when you are finished.
6. See if you can answer these questions based on what you observed:
* What types of foods are high in starch?
* The banana you tested was an unripe one. How do you think a ripe
banana would react with iodine? Why?
EXPLANATION
Iodine reacts with the starch in foods to produce a bluish-black color. Foods
that are high in starch include grain foods and some vegetables such as dried
beans and peas (lima beans, kidney beans, black-eyed peas, garbanzo beans),
potatoes, yams and corn. Less ripe fruits such as the unripe banana, may also
contain a fair amount of starch. The amount of starch decreases as the fruit
ripens, so a ripe banana will not produce a bluish-black color with iodine.
SOURCE: Food Mysteries, Michigan State University
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Updated 8/15/05