Fat in Food

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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.

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.

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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.

Fat in Food

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.

What are lipids?

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

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.

The Translucent or "Grease Spot" Test

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Fat in Food

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.

Distinguishing Between Lipids and Liquids

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

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.

Translucent Spot Test Method

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

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.

Translucent Spots Caused By Other Substances

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Fat in Food

A water spot also makes the paper translucent.

Water Spots

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

1

What is visible through a translucent spot?

Question

A) Everything

B) Only light

C) Only sharp objects

D) Only bright objects

Fat in Food

2

What food substances can turn paper translucent?

Question

A) Water

B) Protein

C) Lipid

D) All of the above

Fat in Food

Lipids do not dissolve in water but form a cloudy liquid called an emulsion.

The Emulsion Test

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

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.

How the Emulsion Test Works

When the lipid molecules are shaken with water they form small beads called micelles.

• Tails that dislike water (hydrophobic)

This is because lipids are made up of molecules that have:

• Heads that like water (hydrophilic).

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Fat in Food

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.

What can go wrong?

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

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.

Positive and Negative Results

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Fat in Food

3

Which of the following is the best way to describe an emulsion?

Question

A) A clear liquid

B) A speckled liquid

C) A cloudy liquid

D) A colored liquid

Fat in Food

4

What is most likely to cause unexpected results when testing foods for fat?

Question

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

The food industry is a multimillion dollar industry. New convenience foods are invented and marketed every day.

Regulating Foods

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

One aspect of the FDA’s jurisdiction over food is regulation of the content of health claims on food labels.

Food Labeling

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

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.

The Food Industry

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

5

What organization regulates food labeling in the United States?

Question

A) The NSA

B) The FSA

C) The FDA

D) The NFA

Fat in Food

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.

Question

Fat in Food

Recognize the reasons for testing foods for lipids

Describe the Translucent Spot test

After completing this presentation you should be able to:

Summary

Describe the Emulsion Test

Explain the importance of food tests in industry

State how food lipids tests are quantified

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