Transcript No Slide Title

Fat in Food
In this presentation you will:
 Recognize reasons for testing foods for fat and oil.
 Investigate two methods commonly used for testing
foods for fat and oil.
 Explore how fat and oil food tests work.
ClassAct SRS enabled.
Fat in Food
Our bodies store energy mostly in
the form of fat, while plants store
their energy as oil. Some vitamins
that we obtain from our food are
only soluble in lipids. This means
that a moderate amount of fats
and oil are essential in our diet.
In this presentation you will
explore the reasons for testing
foods for fat and investigate two
methods commonly used for
testing foods for fat and oil.
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Fat in Food
What are lipids?
Lipids are commonly known as
fats, oils or waxes.
They are a group of energy rich
chemical compounds that contain
fatty acids. Fatty acids are long,
linear chains of hydrocarbons with a
carboxyl group (-COOH) at one end.
Our bodies store energy mostly in the form
of fat, while plants store their energy as oil.
Some vitamins that we obtain from our food are only soluble in lipids. This
means that a moderate amount of fats and oil are essential in our diet.
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Fat in Food
The Translucent or "Grease Spot" Test
You perform this test every time
you buy muffins or doughnuts in a
paper bag. Lipids make unglazed
paper (brown paper, writing
paper) translucent, that is,
transparent enough to allow light
through, but not transparent
enough to be able to see a clear
image through.
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Fat in Food
Distinguishing Between Lipids and Liquids
If a drop of liquid (such as alcohol,
water or oil) falls on paper it
makes a mark which is bright and
translucent when the paper is held
up to the light. With some liquids
the mark disappears as soon as
the liquid evaporates.
Alcohol takes a few seconds to
disappear. Water takes about a
minute, but oil remains, forming a
permanent grease spot. In this way
paper provides a method of
distinguishing between lipids and
other substances.
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Fat in Food
Translucent Spot Test Method
When the translucent or grease
spot test is carried out, food spots
are put onto a piece of unglazed
paper. Typically, filter paper is
used. This can be conveniently
folded up into several sections.
Samples of different foods are
mixed with water or alcohol and
are put onto the filter paper. After
the samples have been allowed to
dry, the filter paper should be held
up to the light. Any samples that
have produced a translucent spot
can be said to contain a lipid.
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Fat in Food
Translucent Spots Caused By Other
Substances
Stains formed by other food
substances, such as protein, can also
make a translucent spot. To distinguish
between a grease spot and a protein
spot, for example, we can dip the paper
into a dish of organic solvent, such as
acetone or ether.
The grease spot will 'disappear' as the
lipid dissolves in the organic solvent,
while a protein stain will remain as a
translucent spot on the paper.
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Fat in Food
Water Spots
A water spot also makes the
paper translucent.
The difference is that, after drying
in air, water is evaporated and the
wet spot becomes clear while the
lipid spot remains translucent.
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Fat in Food
Question 1
What is visible through a translucent spot?
A) Everything
B) Only light
C) Only sharp objects
D) Only bright objects
Fat in Food
Question 2
What food substances can turn paper translucent?
A) Water
B) Protein
C) Lipid
D) All of the above
Fat in Food
The Emulsion Test
Lipids do not dissolve in water but form a cloudy liquid called an emulsion.
To carry out the emulsion test an
extract is made from a food sample,
as with the translucent spot test. A
single drop of this extract is placed
into a test tube. Water is added and
the test tube shaken.
The test tube is observed to see if the
water goes cloudy. An emulsion indicates there is a lipid in the extract.
Without a substance called an emulsifier, such as mustard powder, the
lipid and water will quickly separate again.
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Fat in Food
How the Emulsion Test Works
When the lipid is added to ethanol and
shaken, it dissolves. Then, when this
mixture is poured into water, the lipid
molecules come out of solution and a
white emulsion is formed.
This is because lipids are made
up of molecules that have:
• Tails that dislike water (hydrophobic)
• Heads that like water (hydrophilic).
When the lipid molecules are shaken with water they form small
beads called micelles.
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Fat in Food
What can go wrong?
As with all experiments involving
food and chemical substances, it
is important to avoid
contamination. Incorrect results
are likely to be caused by food
samples that have been mixed up
or contaminated with other foods.
Incorrect conclusions can also be
made if the observer is not sure
what the results mean. Therefore,
make sure you know what the
results are likely to mean.
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Fat in Food
Positive and Negative Results
It is a good idea to make sure that
you know exactly what a positive
and a negative result look like.
You can test a substance that you
know contains a lipid, and another
substance that you know does not
contain a lipid.
For example, use some cooking
oil to see what a positive test will
look like, and water to see what a
negative test will look like. You will
then have some benchmark
results to compare your other
foods against.
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Fat in Food
Question 3
Which of the following is the best way to describe an emulsion?
A) A clear liquid
B) A speckled liquid
C) A cloudy liquid
D) A colored liquid
Fat in Food
Question 4
What is most likely to cause unexpected results when testing
foods for fat?
A) Dissolving the fatty food in ethanol
B) Mixing foods up accidentally
C) Using tap water instead of distilled water
D) Using solid foods instead of oil
Fat in Food
Regulating Foods
The food industry is a multimillion dollar industry. New convenience foods
are invented and marketed every day.
The United States Food and
Drug Administration (FDA) is
the government agency
responsible for regulating food
(human and animal), dietary
supplements, drugs (human and
animal), cosmetics, medical
devices (human and animal),
biologics and blood products in
the United States.
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Fat in Food
Food Labeling
One aspect of the FDA’s
jurisdiction over food is regulation
of the content of health claims on
food labels.
The Fair Packaging and
Labeling Act is a US law that
applies to labels on many
consumer products. It requires a
product’s label to state the
amounts of nutritional constituents
of the product.
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Fat in Food
The Food Industry
In the food industry, food tests have to be
quantitative. This means that the exact amounts
of the nutritional components of food have to be
worked out.
Quantitative food tests
are carried out using a
technique known as
photo-spectrometry.
When the food test has been carried out, the solution or suspension in the
test tube is put into a machine (a photo-spectrometer) that measures the
amount of light passing through the solution or suspension.
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Fat in Food
Question 5
What organization regulates food labeling in the United States?
A) The NSA
B) The FSA
C) The FDA
D) The NFA
Fat in Food
Question 6
Photo-spectrometers are used to measure the amount of fat in
food. An emulsion made with a high fat food would allow less
light to pass through it compared to an emulsion made with a
low fat food.
Answer True or False.
Fat in Food
Summary
After completing this presentation you should be able to:
 Recognize the reasons for testing foods for lipids
 Describe the Translucent Spot test
 Describe the Emulsion Test
 Explain the importance of food tests in industry
 State how food lipids tests are quantified
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