Experiment to Find Out Energy Content of Various Foods


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Experiment to Find Out Energy Content of Various Foods

Problem
=======

For this piece of coursework, I intend to design and carry out an
experiment to find out the energy content of various foods.



Method
======

For my experiment I have chosen four different foods that I will test
for energy content, they are sweetened banana chips, toffee popcorn,
original flavour Hula Hoops and salted peanuts. I will use the
following apparatus and will set it up as shown:

For the experiment all I am going to have three variables, the food
that I use, temperature of the water and the weights of the food won't
all be equal, everything else will be kept the same, the distance of
the candle from the test tube, the amount of water in the test tubes,
etc.

I will fill the test tube with 25cm3 of water using a measuring
beaker. I will do three or four tests of each food as to obtain an
accurate result and a good average. For each specimen I will find the
starting weight, and the starting temperature of the water in the test
tube. For the actual experiment I will start off by attaching the food
to a spike and then setting it alight by the use of a candle. I will
need to make sure that the candle is not too far nor too close to the
test tube so as it won't affect the temperature of the water. As soon
as the piece of food is alight I will quickly move it over to under
the test tube so that not too much energy is lost during the period of
movement between the test tube and the candle. I will hold the item of
food under the test tube until the flame goes out, continuously
stirring the water so as I don't get what is called a thermocline
(when the water forms layers due to differences in temperature), with
a warm layer and a colder layer of water. Once the piece of food has

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burnt out, I will check the temperature of the water once again and
record it. Next I'll weigh the food and record this as well. Finally,
for the calculations to find out how much energy each food has in kJ I
will use the following equation:

Temperature rise in oC * Volume of Water in cm3 * 0.0042 = Energy
content in kJ

This gives you the amount of kJ per however much the food weighs but I
want to find out how many kJ there are per 100g so I will do the
following:

100/Weight Burned * Energy content = Amount of kJ per 100g

I will do this for all three tests and then find the average (All
results added together divided by number of results). Then I will
follow all of these tests for the other three foods.



Prediction
==========

If I want to make a good and accurate prediction then I need to look
at the composition of each food (e.g. amount sugars and proteins in
it), to help me.

Protein

Carbohydrates

Fats

Fibre

Sodium

Salted Peanuts

29g

5g (4g sugars)

53g (saturated-10g)

9g

0.6g

Toffee Popcorn

3g

77g (50g sugars)

9g (saturated-7g)

6g

0.5g

Original Flavour Hula Hoops

3.2g

55.3g (1g sugars)

31.4g (saturated-14.2g)

2.2g

1.2g

Sweetened Banana Chips

1g

59g (22.1g sugars)

31.4g (saturated-13.6)

1.7g

0.005g

Note: All amounts are per 100g.

I think that the more proteins, fats, and carbohydrates the food
contains the more energy it will be able to supply and thus the longer
it will burn. I say this because fats are broken down into fatty acid
molecules and glycerol molecules, proteins are broken down into amino
acid molecules and carbohydrates are broken down into glucose
molecules (these are broken down during the process of digestion they
don't just break down at random). All of these provide energy so, as
said before, the more there are the more energy you get. So my
prediction is that the sweetened banana chips will contain the most
energy.

Calculations (using the equations previously listed):

Food

Energy Content (kJ) of individual pieces

Energy Content per 100grams (kJ)


Sweetened Banana Chips
----------------------

Test 1

5.36

205.17

Test 2

4.73

390.50

Test 3

3.68

382.81

Toffee Popcorn

Test 1

0.89

55.78

Test 2

2.31

360.94

Test 3

1.68

730.43

Test 4

1.26

323.08

Original Flavour Hula Hoops

Test 1

1.52

323.94

Test 2

2.68

243.41

Test 3

3.78

366.99

Test 4

3.89

431.67


Salted Peanuts
--------------

Test 1

3.36

840.00

Test 2

5.15

791.54

Test 3

6.41

1307.14

Test 4

3.47

707.14

Averages:


Food
----

Energy Content (kJ) of individual pieces

Energy Content per 100grams (kJ)

Sweetened Banana Chips

4.59

326.16

Toffee Popcorn

1.84

344.67

Original Flavour Hula Hoops

2.97

341.5

Salted Peanuts

4.6

911.45

When going back to my original prediction it looks as if it was quite
the wrong idea as, when looking at the results, one can see that the
sweetened banana chips do not contain the most energy, as I thought,
instead the salted peanuts do. Following is a table of the energy
contents that were listed on the packets:


Food
----

Energy Content per 100grams

Sweetened Banana Chips

2137kJ

Toffee Popcorn

1700kJ

Original Flavour Hula Hoops

2156kJ

Salted Peanuts

2530kJ

As can be seen a comparison between the energy contents listed on the
packets and the results from the experiment there is a significant
difference. When my original prediction is compared to the energy
contents listed on the packets it looks almost as if my prediction was
still quite far off, here, the sweetened banana chips contain the
third greatest amount of energy.

[IMAGE]
Evaluation

As can be seen by comparisons between actual energy contents and
results I got, the experiment was probably not very accurate, though
this is not because the experiment was done wrongly. There were so
many things that could not be helped in the experiment. A large amount
of heat was lost in the form of heat. Heat was absorbed by the
surrounding air, energy was lost during the transition of the burning
food from the candle to the test tube. Another source of heat loss was
the test tube itself. The test tube was heating up as well as the
water and heat was escaping form it into the air. Another factor was
that there were probably plenty of air currents flowing through the
room both warm and cold, warm from other peoples candles and cold from
the outside air. These air currents probably affected the temperatures
of the water and the flame of the burning food in quite a big way.
Another factor is the oil, grease and fat that dripped off of the food
as it burned, these drops would have been enough energy to keep the
food burning for a while longer than it would actually have done. I
would say that all of these uncontrollable variables were what
affected my results, making them as low as they were.

Despite the fact that my results may not exactly have been superbly
accurate, they are still reliable enough to base a firm conclusion on.
I can tell from my results that the salted peanuts contained the most
energy, probably because of the salt on them, which I did not take
into account when I was making my predictions. I can also tell that
the ones with a smaller energy content were the original flavour Hula
Hoops and the toffee popcorn.

To improve my method and increase the reliability and accuracy of my
results there are a few things that I would have done. Primarily I
would have tried to decrease the amount of oil that dropped off of the
burning food, possibly by putting the food on a ceramic tile instead
of on a spike so that any oil would still be burnt. Another thing I
would have tried to change is the method of setting the food alight,
since so much energy was lost that way.

Another experiment that could be performed to more accurately discover
the energy contents of different foods is the same experiment that is
used to oxidize sugar. The setup of apparatus is shown below:

This experiment would be far more accurate for quite a few reasons.
First of all no real amount of energy is lost through the air as the
burning sugar is surrounded by the water that it is supposed to be
heating up. No heat is lost through the heating of the test tube (or
in this case the jar or beaker which contains the sugar) because
although it is heated, the heat only serves to heat up the water even
more. No energy is lost during a transition of the lighted food to the
jar as it is lighted in the jar. The hot gases that rose off of the
food while it was burning was wasted during my experiment but for this
experiment it heats the water as it rises since the tube which it
rises through is also surrounded by water. So, overall this experiment
is a far more accurate way of measuring the energy content of foods.


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