Feeding Frenzy…What am I eating, anyway?
Around the world, different cultures have developed an assortment of diets which reflect their
agricultural conditions, customs, and tastes. As different as they may seem at first glance, most of these diets
supply the same nutritional requirements needed by humans to sustain life. What are these nutritional
requirements needed by humans to sustain life. What are these nutritional requirements and how can such
different food sources as beef, rice, beans, insects, and vegetables all supply them?
How can we determine whether foods that seem so different in appearance are actually made up of
the same or different components? In this investigation, you will identify some of the components of food
which are required to sustain life. These components which make up food are called nutrients. A nutrient is
considered “essential” when it cannot be synthesized by the organism but must be obtained by the organism
from its environment.
You will be using indicators as chemical detection tools to find out what nutrients are present in food.
Indicators are chemical compounds used to detect the presence of other compounds. Detection is based upon
observing a chemical change that is taking place. The substance being detected and the indicator are
involved in a chemical reaction which brings an observable change-most often, a change in color.
Procedure
1.
Collect your group’s food samples. Predict which nutrients are present in each sample you are about
to test. Record your predictions in the table below by filling in the boxes with yes or no.
Food Sample
Protein Present ?
Sugar Present ?
Starch Present ?
Fat Present ?
Turkey
Potatoes
Corn
Pumpkin
Whole Milk
2. Your teacher has established the positive and negative controls for the experiment. A positive
control shows you the color change that occurs when the indicator reacts with the nutrient that it
tests for. A negative control mixes the indicator with water so that there is no reaction. You should
obtain these controls from your teacher. Use these to determine if your tested food samples include a
particular nutrient. Record the color in the positive and negative controls in the table.
Nutrient
Indicator
Protein
Biuret
Sugar
Benedicts
Starch
Iodine
Lipid
Sudan IV
Positive Reaction
Negative Reaction
3. Test for Sugar. This test uses Benedicts solution and must be heated for a chemical reaction (and color
change) to occur. Because of this, the set up is slightly different and should be completed first. The
test tubes will need to be heated for about 10-15 minutes for the color change to occur.
a) obtain 5 test tubes and use tape to label each with the following information
i. type of food
ii. your group (initials or name…but you will need to know which tubes are yours)
b)
c)
d)
e)
place a small sample of each food into the appropriate test tube
add 15 drops of Benedict’s indicator to each of the test tubes
place your test tubes in the hot water bath located at the front of the room.
Wait 10 minutes, then check your samples (during this time you should begin the other tests).
If none have changed leave them for 5 more minutes. If the color change has occurred in
some of your test tubes, you can retrieve the tube and record your results in the table below.
f) Clean out (use water, brush & soap) and return your test tubes to the dispensing table.
4. Tests for Protein, Starch and Fat. The protein fat uses Biuret solution, starch uses iodine and Fat uses
Sudan IV. These do not need to be heated and should be conducted using the well plate. All 5 foods
can be tested for all three nutrients in one well plate.
a) obtain 1 well plate
b) Place a small sample of each food into the appropriate wells following the guide shown
below. (The left side and top of the well plate are lettered and numbered as shown)
A
B
C
1
Turkey
Biuret
Turkey
iodine
Turkey
Sudan
2
Potato
Biuret
Potato
iodine
Potato
Sudan
3
Corn
Biuret
Corn
iodine
Corn
sudan
4
Pumpkin
Biuret
Pumpkin
iodine
Pumpkin
sudan
5
Milk
Biuret
Milk
iodine
Milk
sudan
6
Empty
D
Empty
c) Using the guide shown above, add 5-7 drops of each of the indicators to the well plate. Be
sure to follow the format and test each food with each indicator.
d) Look for the resulting color after you add the indicators. You may need to stir the samples
with a wooden stick. Also, check the color from the bottom of the well plate to see if the
indicator has settled. Some food samples that have their own color are hard to judge…look
closely.
e) Record THE COLOR you see in the following table..
Results
1. Record the color you see after each of the tests. This color should either be the color change or the original
color of the indicator. (Example: Iodine = black if + or red/brown if -)
Indicator
Benedicts
Biurets
Iodine
Lipids
Turkey
Potato
Corn
Pumpkin
Whole Milk
Conclusion
1.
Based on your observations, what function do negative controls serve?
2. What function do positive controls serve?
3. Based on your results above which nutrients are in each of the foods
Food
Nutrients Present
Turkey
Potato
Corn
Pumpkin
Whole
Milk
4. Based on these foods and nutrients, what nutrients do you think are hardest to get or lacking in your
own diet?
5. What is the function of each of the nutrients? What do they do for us? Why are they needed in the
body? If you consider your nutrient needs to be 100% in a day, how much of this should be from each
of those below?
Nutrient
% of diet Function
Protein
Carbohydrates
(Sugar &
Starch)
Fat