Fruit Juicy Experiments
FOOD EXPERIMENT: COLOR
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.
FRUIT JUICY EXPERIMENT
INTRODUCTION
Fruits and vegetables contain pigments that give us the rainbow of possible
colors in these foods. Because of these colors, fruits and vegetables add a
lot of interest to our meals. Can you imagine what meals would be like if we
ate only white foods at every meal?
The pigments called anthocyanins (an-tho-SY-a-nins) give several foods their
red, blue or purple color. The anthocyanins change color depending on whether
they are in contact with an acid or a base. Try this experiment to see how
you can change the color of fruits!
INGREDIENTS
3/4 cup cranberry juice
1/2 teaspoon baking soda
1 tablespoon lemon juice
EQUIPMENT
3 custard cups or clear glasses
Measuring cup - liquid
Measuring spoons
Sheet of white paper
Masking tape
Marker
Spoon for stirring
PROCEDURE
1. Place the custard cups or clear glasses on the white paper. Label each cup
or the paper with the masking tape and marker like this:
Cup 1 CRANBERRY JUICE
Cup 2 CRANBERRY JUICE + BAKING SODA
Cup 3 CRANBERRY JUICE + BAKING SODA + LEMON JUICE
2. Add 1/4 cup cranberry juice to each cup.
3. Add 1/4 teaspoon baking soda to cups 2 and 3. Stir.
4. Record what you see:
Cranberry juice ............................ = ______________________ color
Cranberry juice + baking soda .............. = ______________________ color
5. Now add 1 tablespoon lemon juice to cup 3. Record what you see:
Cranberry juice + baking soda + lemon juice = ______________________ color
6. See if you can answer these questions based on what you observed:
* Which cup represents your "control"? (Remember, a control is the standard
against which you compare the experiment.)
* Cranberry juice is an acid solution that contains anthocyanin pigments.
What does the solution become when baking soda is added to the juice?
What color change did you see when the baking soda was added?
* What did the baking soda/juice solution change to when the lemon juice
was added? What color change did you observe when the lemon juice was
added?
EXPLANATION
Why did the juice change colors? Cranberry juice is an acid that contains the
anthocyanin pigment. In acid, this pigment is red. When baking soda was
added to the cranberry juice, the juice became less acid and more like a base.
Anthocyanin pigments turn blue in a base. When the color is blue, you can
reverse it by adding an acid such as lemon juice. This action makes the
cranberry juice acid again and the color changes back toward red.
You probably also observed fizzing when the baking soda was added to the
cranberry juice. The fizz is from bubbles of carbon dioxide gas. The gas is
formed when an acid (cranberry juice) is mixed with a base (baking soda).
SOURCE: Food Mysteries, Michigan State University
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Updated 8/15/05