talk about Energy Content of Foods (using the Scientific Method)

mohism1

lab_test_food_as_fuel.pdf

Home >Chemistry homework help >talk about Energy Content of Foods (using the Scientific Method)

Energy Content of Foods (using the Scientific Method)

Lab Objective

This laboratory experiment will allow the student to systematically investigate a real

world problem involving the energy content of foods. The student will apply the scientific

method in defining the problem, proposing a hypothesis, using the literature to gain

background information pertinent to the problem, designing an experimental approach to test

the hypothesis (drawing upon techniques learned in previous experiments), analyzing the data,

developing conclusions from the data, and examining limitations to the experimental approach

which was used.

I. The Problem

Consider the following questions and state the problem which you will investigate.

Do all foods provide the same amount of energy?

Can foods be used as fuel?

Are the Calories on a food label the same as the calories in chemistry class?

________________________________________________________________________

II. Hypothesis

Propose an answer to your problem/question.

_______________________________________________________________________

III. Background Research

Using the literature provided, find answers to the following questions:

A. Why is the energy value in foods important?

_____________________________________________________________________

B. What does “Calories” on a food label tell a consumer?

___________________________________________________________________________

____________________________________________________________________________

_____________________________________________________________________

C. Describe two methods for determining the energy value of foods.

____________________________________________________________________

___________________________________________________________________________

_____________________________________________________________________

D. What is the source of the energy released by foods?

_________________________________________________________________________

_____________________________________________________________________

E. How are metabolic reactions (particularly respiration) and combustion reactions similar

and how are these reactions different?

__________________________________________________________________________

___________________________________________________________________________

_____________________________________________________________________

F. Why do some things which we eat have no caloric value (eg. water, artificial

sweeteners)?

____________________________________________________________________________

_____________________________________________________________________________

IV. The Experiment

Review the”Energy Content of Fuels” lab from earlier in the semester. Look at the

suggestions for mounting samples. Design an experiment which will test your hypothesis.

Write the experimental procedure out stepwise. Sketch your apparatus.

Construct a data table on which you will record all measurements and

observations.

After talking with your instructor, run your experiment.

Materials needed:_______________________________________________________________

______________________________________________________________________________

_______________________________________________________________________________

Procedure:______________________________________________________________________

_______________________________________________________________________________

Apparatus diagram (Label all components of apparatus):

Data Table (include all masses, temperatures and reference data):

V. Data Analysis

Use your data to calculate the energy content of the foods. Compare your

measured values to those on the food packaging (% error).

VI. Conclusion

Restate your hypothesis indicating whether your results proved or disproved your

hypothesis.

________________________________________________________________________________

VII. Further Reflections

A. The results you obtained were not the same as those reported on the food packaging.

This may be due to (1) the crudeness of the experimental apparatus, (2) the

inexperience of the experimenter, and (3) the limited number of measurements made.

What would you need to do to remedy each of these problems? Why is each of these

remedies not possible today?

_______________________________________________________________________________

________________________________________________________________________________

_______________________________________________________________________________

________________________________________________________________________________

_________________________________________________________________________________

B. Artificial sweeteners are molecules containing the same atoms found in carbohydrates,

fats and proteins. These molecules should be able to burn (combust). Why would the

experiment which you designed not be useful when predicting the caloric value of

artificial sweeteners? (1) Consider possible difficulties you might encounter trying to

mount and burn the sample. (2) Consider your answers to the questions in the

“Background Research” section. How useful would an experimental heat of combustion

be in predicting your body’s ability to get energy from the sweetener?

________________________________________________________________________________

_________________________________________________________________________________

__________________________________________________________________________

Food as Fuel Lab – Reference Paper

The food you eat provides the building blocks for your tissues, as well as the energy required for life.

Body temperature maintenance, the growth of new tissue, digestion, locomotion, and the metabolic

response to food are among your life processes which consume energy. The amount of energy that your

body needs for these processes is usually defined in terms of your basal metabolic rate (BMR) and basic

energy requirements (BER). The BMR is the minimum caloric requirement needed to sustain life in a

resting individual. Your BER includes your basal metabolic rate and your general daily activities. When

your ingested food provides more energy than is required for your BER, the extra energy is stored by

your body in the bonds of fat molecules. If you desire to maintain a healthy body weight, you should

consume only enough food to meet your BER and any extra energy requirements (exercise).

Units of Food Energy

The energy content of food is measured in Calories (Cal). A Calorie is the amount of energy required to

raise the temperature of 1 kg (1 L) of water 1°C (from 14.5 to 15.5°C). A Calorie is the same amount of

energy as a chemist’s kilocalorie. Although the International System of Units (SI) favors the use of the

joule (1 kilocalorie = 4.184 kilojoules), many scientists and most consumers continue to use the Calorie.

Thus the energy content listed on food product labels is expressed in this Calorie.

Source and Storage of Food Energy

Energy is stored in food as chemical potential energy. This occurs when biological processes in plants

(such as photosynthesis and amino acid biosynthesis) and in animals (such as protein biosynthesis and

lipogenesis) lead to the formation of carbohydrates, proteins, and fats. When the chemical bonds in

these macronutrients are broken, energy is released. At the cellular level, a set of oxidation-reduction

reactions involving these nutrients and molecular oxygen (O2) ultimately leads to the formation of

adenosine triphosphate (ATP). Carbon dioxide and water are released as waste products. This set of

reactions is known as cellular respiration and occurs step-wise, relying upon enzymes to catalyze each

step. The ATP serves as an energy storage molecule which can readily release its energy in other

metabolic pathways.

Measurement of Energy Content in Foods

The energy value of a food may be determined using a bomb calorimeter like that in Figure 1 below.

The food is burned completely in the presence of O2 to form carbon dioxide and water (this reaction is

known as combustion). The energy released in the form of heat is determined from the change in the

temperature of the water bath surrounding the reaction bomb. The energy value determined through

bomb calorimetry is the maximum amount available. However, not all of this energy is available to you

for your life processes.

Another method for determining a food’s energy value considers the macronutrient composition of the

food. The average heats of combustion for the macronutrients are 9.4 kcal/g for lipids or fats, 5.65

kcal/g for proteins, and 4.2 kcal/g for carbohydrates. You can calculate the gross energy value for a food

of known composition from these average heats. If you consider your body’s ability to digest and

absorb each of these nutrients, you can arrive at the net energy actually available to your body. Wilbur

Atwater, a 19 th

-century chemist, determined a set of general factors for carbohydrates (4 kcal/g), lipids

(9 kcal/g), and proteins (4 kcal/g) which allow you to estimate the usable energy content of your daily

diet.

Figure 1. A bomb calorimeter.

“Foods “ with No Calories

The amount of energy available from “food” is generally related to the number of carbon-hydrogen

bonds per gram. Thus fats, which consist primarily of carbon and hydrogen, have the highest caloric

content of the macronutrients. In contrast, carbohydrates contain a significant amount of oxygen

(fewer C-H bonds per gram) and provide only half the number of calories per gram that fats do. Water,

H2O, contains no carbon. Although this substance is vital to life, it is not a source of energy. Many

sweeteners used in food also do not provide any caloric content. These substances are organic

compounds (contain C-H bonds) and may be very similar in chemical structure to the macronutrients.

The “zero calories” label results either from the body’s inability to metabolize the sweetener (eg.

Splenda sweetener) or from the extremely small quantities which must be added to food to increase

sweetness (eg. saccharin).

References

http://www.cristina.prof.ufsc.br/v2/digestorio/mcardle_energy_value_food_ch4_connection.pdf

http://www.healthyeatingclub.org/info/books-phds/books/foodfacts/html/data/data2a.html

http://www.fao.org/DOCREP/006/y5022e/y5022e04.htm

http://www.dairyscience.info/packaging-/119-labelling-determination-of-the-energy-content-of-

food.html

Useful reference for experimental design:

http://www.biologyjunction.com/energy_in_food.htm

http://www.cristina.prof.ufsc.br/v2/digestorio/mcardle_energy_value_food_ch4_connection.pdf

http://www.healthyeatingclub.org/info/books-phds/books/foodfacts/html/data/data2a.html

http://www.fao.org/DOCREP/006/y5022e/y5022e04.htm

http://www.dairyscience.info/packaging-/119-labelling-determination-of-the-energy-content-of-food.html

http://www.biologyjunction.com/energy_in_food.htm