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FOOD CHEMISTRY EXPERIMENT BOOK

Unit 2. LIPIDS

Teacher Activity Guide

Student Activity Guide

Figure 1

Activity/Experiment

Freaky Fats

Phats


Unit 2. LIPIDS

Teacher Activity Guide

Expected Outcomes

The student will learn about sources of lipids and their uses in the food industry.

Activity Objective

Students will make visual observations of fat and then extract and examine the invisible fat from chocolate, potato chips, and sunflower seeds.

Activity Length

Part A - 20 minutes.
Part B - 40 minutes to perform the experiment, dry overnight, 10 minutes the next day to record observations.

Scientific Principles

In this experiment, acetone is used to extract the invisible fats, since lipids are sparingly soluble in water but soluble in organic solvents. When the extraction is complete, the students will be able to see, touch, and smell the lipid in the Petri dishes and be able to determine if it contains saturated or unsaturated fatty acids. The cocoa butter found in chocolate chips is a saturated fat and will be solid at room temperature. The oils used to fry the potato chips are unsaturated and will be liquid at room temperature. The oil from the sunflower seeds also is unsaturated and will be liquid at room temperature.

Vocabulary

Acetone is a clear, colorless, flammable, fruity-smelling organic (carbon-containing) liquid used to make many other chemical compounds. It is also formed in diabetic people, and its presence in urine is one symptom of this disease.

Emulsion is a property where two liquids are evenly spread out in each other, yet not dissolved in each other. Oil and water form the most common emulsions, and milk is an emulsion of butterfat in water. Emulsions are important in the production of foods that contain water and fat, such as mayonnaise or margarine. These products require the addition of an emulsifier, such as the food lipid lecithin, to stabilize food emulsions.

A fatty acid is a carboxylic acid derived from or contained in an animal fat or vegetable oil. All fatty acids are composed of alkyl groups or hydrocarbon chains containing from 4 to 22 carbon atoms and characterized by a terminal carboxyl group COOH. Fatty acids are the building blocks of fats, having hydrogen atoms attached to chains of carbon atoms. Fatty acids are found in every cell of the human body.

Insoluble means not capable of being dissolved. Fats are insoluble in water (fat is non-polar, and water is very polar). Fats are soluble in like solvents. As an example, fats are soluble in non-polar solvents such as acetone and ether. On the other hand, sugar will not be soluble if more is added than what a certain volume of water can dissolve, which means that the solvent has become saturated with sugar.

Lipase is a generic name given to a group of enzymes that catalyze the hydrolysis of lipids. For example, a lipase that works on food lipids breaks down triacylglycerol into glycerol and fatty acids.

Lipids are compounds of fatty acids and glycerol. Lipids are the most efficient source of fuel in living things; they are stored beneath the skin in animals and the human, and mostly in the seeds of plants. Food lipids are divided into fats, which come from animal sources and are solid at room temperature, and oils, which come from plant sources and are liquid at room temperature. Another type of lipid is cholesterol. Cholesterol is a sterol compound made by animals and is used to make certain steroid hormones in the body. It is not found in plants.

Mass is the quantity of atoms or matter in an object. As the mass of an object increases, so does the degree of difficulty to change the motion (or lack of motion) of an object. This is also referred to as a measure of inertia. A locomotive has more atoms than a car and therefore more mass. It also has much greater inertia, requiring a much greater force to change its movement.

Organic means related to the branch of chemistry dealing with carbon compounds. Though all living things contain carbon and thus are considered to be organic, other carbon-containing compounds have been produced in the laboratory.

Quantitative describes a measurable amount or number value for something. For example, a white, round (qualitative) piece of filter paper weighs 1.32 grams (quantitative).

Soluble means capable of being dissolved. Gases or solids that dissolve are called solutes, while the liquid that does the dissolving is called the solvent. Like substances are usually soluble in like solvents.

A triacylglycerol is a lipid compound consisting of three fatty acids linked to one glycerol molecule. This compound is an important source of energy for the human body. To utilize this compound for energy, enzymes called lipases must first hydrolyze it to liberate the fatty acids that are chemically bonded to glycerol.

Materials Required

  • Chocolate chips (semi-sweet)
  • Balance or scale
  • Sunflower seeds
  • Microwave
  • Potato chips
  • Paper towels
  • Acetone
  • Foil
  • 100-mm Petri dishes
  • Hammer
  • 100-and 600-milliliter beakers
  • Safety goggles
  • Graduated cylinder
  • Latex or rubber gloves

Instructional Strategies and Procedures

This activity could be conducted over one class period if the students are assigned to groups that focus on the separate aspects of the lipid experiments.

Teaching Tips

  • The foods produced in these experiments are not to be consumed.
  • Use acetone purchased from a local hardware store. Acetone is normally used as a thinner for epoxies, lacquers, and adhesives. The acetone will evaporate in one hour from the chocolate and potato chips. You will have to smell the sunflower seeds to determine if the acetone is gone. Do not use nail polish remover or rubbing alcohol because they contain too much water to extract the lipid.
  • You may substitute mineral spirits or denatured alcohol purchased from the hardware store for the acetone.
  • Have the students wear latex gloves and safety goggles when handling the acetone solvent.
  • Perform this experiment in a well-ventilated area.
  • The acetone is highly flammable. Be sure there are no flames or pilot lights on in the room.
  • Semi-sweet chocolate chips contain more fat than milk chocolate chips.
  • You may substitute walnuts for sunflower seeds.
  • Try to use low-salt potato chips; do not use low-fat or baked potato chips because these products have much less lipid.

Part A

SAMPLE DATA TABLE – VISUAL OBSERVATIONS OF FAT

Food Describe what you see on the paper towel
Chocolate chips Grease spot spreads beyond the chocolate
Potato chips Large, wet grease spot on the paper towel
Sunflower seeds Grease spot is only where the seeds touch the paper

Part B SAMPLE DATA TABLE – EXTRACTION OF LIPIDS

Food Weight of beaker Weight of beaker with raw food Weight of raw food Weight of beaker with dried food Weight lost from food % Lipid extraction
Chocolate chips 49 g 53.4 g 4.4 g 53.2 g 0.2 g 4.5%
Potato chips 48.6 g 53.2 g 4.6 g 52.7 g 0.5 g 10.9%
Sunflower seeds 51.1 g 55.5 g 4.4 g 54.8 g 0.7 g 15.9%

(weight of beaker with raw food) – (weight of beaker) = weight of raw food

(weight of beaker with raw food) – (weight of beaker with dried food) = weight lost from the food

(weight lost from food / weight of raw food) x 100 = % lipid extracted

Part B SAMPLE DATA TABLE – DESCRIPTION OF FAT

Food Color * Texture * Odor * Viscosity *
Chocolate chips Light brown Waxy Smells like chocolate Hard, dry
Potato chips Light yellow Oily Corn Thick oil
Sunflower seeds Yellow Oily Sunflower seeds Thick oil

*Results reported were obtained using the following products: Nestlé ® semi-sweet chocolate chips, Jays ® Potato Chips (fried in native corn oil), and Pic-A-Nut ® sunflower seeds (shelled).

 

Key Questions and Answers

  1. How can you tell that the dark wet spot on the paper towel is fat and not water?
     
    The paper is transparent, and it’s greasy to the touch.
     
  2. Rank from most to least the percentage of lipid extracted from all three foods. Look at the Nutrition Facts label on the packages of all three foods and rank them. Did your ranking agree with the ranking of the product labels?
     
    Sunflower seeds, potato chips, and chocolate chips. From the Nutrition Facts labels: 28 grams of sunflower seeds contain 15 grams of fat; 28 grams of potato chips contain 10 grams of fat; and 28 grams of chocolate chips contain 8 grams of fat. Yes, the rankings are consistent.
     
  3. Determine which lipids contained saturated and unsaturated fatty acids in this experiment, based on your descriptions of the fats in the Petri dishes.
     
    The lipid extracted from the chocolate contained saturated fatty acids. The lipid extracted from the potato chips contained unsaturated fatty acids. The lipid extracted from the sunflower seeds contained unsaturated fatty acids.

Web site for more information on lipids

http://biology.clc.uc.edu/courses/bio104/lipids.htm - Information about lecithin, sources of lecithin, and how it is used in foods and other applications.

Student Activity Guide

LIPIDS

Lipids include fats, oils, waxes, cholesterol, other sterols, and most steroids. In the body, fat serves as a source of energy, a thermal insulator and cushion around organs, and an important cellular component. The fat-soluble vitamins are A, D, E, and K. You are probably most familiar with the nutritional aspects of dietary fats and oils. Since fats have 2.25 times the energy content of carbohydrates and proteins, most people try to limit their intake of dietary fat to avoid becoming overweight. The food industry has a big market for low-fat and non-fat foods. Just take a look around your local grocery stores!

Lipids are classified as organic compounds that are soluble (dissolvable) in organic solvents, but only sparingly soluble in water. Lipids are biologically important for making barriers (membranes of animal cells), which control the flow of water and other materials into a cell.

Fats and oils make up 95% of food lipids and phospholipids, and sterols make up the other 5%. Traditionally, fats were considered to be solid at room temperature, and oils were considered to be liquid. However, this designation is often used to distinguish between fats and oils from animals and plants, respectively. Animal fats are found in meats (beef, chicken, lamb, pork, and veal), milk products, eggs, and seafood (fish oil). Plant (vegetable) oils come from nuts (peanuts), olives, and seeds (soybean, canola, safflower, and corn). We use lipids for flavor (butter and olive oil), to cook foods (oils and shortening), to increase the palatability of foods by improving the texture or “mouthfeel” (cakes, creamy ice cream), and in food processing (emulsifiers).

Fatty acids are generally long, straight chains of carbon atoms with hydrogen atoms attached (hydrocarbons) with a carboxylic acid group (COOH) at one end and a methyl group (CH3) at the other end. These long, straight chains combine with the glycerol molecule (see Figure 1A) to form lipids (glycerol lipids).

Figure 1

A. Glycerol molecule is the backbone of a glycerol lipid. The triacylglycerol contains three fatty acids attached at the oxygen atoms of glycerol.

B. Configuration of a cis double bond.

C. Configuration of a trans double bond.

D. Linoleic acid is an essential fatty acid containing two double bonds. It is needed for growth and health.

E. Stearic acid is a saturated fatty acid found in foods from animal and plant sources.

F. Milk fat triacylglycerol molecule illustrating the ester bonds between fatty acids and glycerol.


Most naturally occurring fatty acids contain an even number of carbon atoms. The 18-carbon fatty acids are the most abundant in our food supply; examples are linoleic acid (an omega-6 fatty acid) found in corn oil and linolenic acid (an omega-3 fatty acid) found in flaxseed oil. Linoleic and linolenic acids are considered
essential fatty acids because they are needed for normal physiological functions and our body cannot make them. We need to get these fatty acids from food sources. These fatty acids are found in the vegetable oils used in several different food products.

Structure of Lipids

Most of the carbon-carbon bonds in fats are single bonds, which allow the carbons to freely rotate, making the attached groups chemically identical. However, the number of unsaturated bonds (double bonds) may vary from one to many in the hydrocarbon part of the fatty acid. Since double bonds do not allow free rotation between the attached carbons, any attached chemical groups are fixed in their respective positions.

There are two possible orientations for groups attached to the carbons in a double bond. If they are on the same side of the double bond (close together), they are in the cis conformation. The opposite of the cis conformation is the trans conformation, where the residues at ends of the double bond are farther apart. Double bonds in natural vegetable oils and in animal fats are mostly in the cis conformation (see Figures 1B and 1C); however, a few exceptions are known where the trans conformation is present.

The presence of the double bonds is responsible for the liquid properties of native vegetable oil. Because the cis double bonds are “kinked”, they disrupt the physical interactions between fatty acid molecules, preventing them from packing together tightly to form crystals (see Figure 1D, structure of linoleic acid). This disruption keeps the fatty acid molecules from associating with each other, resulting in a liquid structure. If the double bonds are removed by adding hydrogen (hydrogenation), the kinks are removed, allowing the fatty acid molecules to more easily associate with each other (see Figure 1E, structure of stearic acid). The result is crystallization (solid fat) at room temperature.

Depending on how the various fatty acid chains associate, the crystalline structure of the solid fat can have different appearances, such as a smooth, shiny solid or a rough, puffy solid. These crystalline forms also have different light-reflection characteristics and physical hardness. This difference in physical properties is used when making shortening, which is crystallized into a very white, soft crystalline form at the factory. However, upon melting and re-solidification, it becomes more translucent and grayer, due to the formation of a different crystal structure.

Nomenclature for Fats

If all the bonds are single, the fatty acid molecule is saturated, because the maximum number of hydrogen atoms is associated with the carbon atoms. Some examples are tallow (beef fat), lard (pork fat), and butter (milk fat). If there is a double bond among the carbon atoms, the fatty acid molecule is unsaturated. Examples of unsaturated fats are canola oil, corn oil, cottonseed oil, and soybean oil. If there are multiple double bonds (two or more), it is called polyunsaturated. You may recall seeing the saturated, unsaturated, and polyunsaturated terms with respect to nutritional aspects of oils. Corn and soybean oils are some of the most important food sources of polyunsaturated fatty acids in our food supply. Shown below are the shorthand notation used to describe some important food sources of 18-carbon (C18) fatty acids.

  • C18:0 is a fully saturated 18-carbon fatty acid called stearic acid.
  • C18:1 has one double bond, between carbons 9-10, (18:1n9) counting from the
  • COOH end, and is called oleic acid.
  • C18:2 has two double bonds, between carbons 9-10 and 12-13, counting from the
  • COOH end, and is called linoleic acid (9,12-octadecadienoic acid or 18:2n6).
  • C18:3 has three double bonds at carbons 9-10, 12-13, and 15-16, counting from the
  • COOH end, and is called linolenic acid (9,12,15-octadecatrienoic acid or 18:3n3).

The number of fatty acids joined to the glycerol molecule also plays a part in how the molecule is named. If only one fatty acid is connected, the general name for the molecule is a monoacylglycerol. If two are joined, the molecule is called a diacylglycerol, and if three are joined, a triacylglycerol. The bond between the fatty acid and the glycerol also has a special name. It is called an ester bond (see Figure 1F). The carboxyl end (COOH) of the fatty acid molecule attaches to one of the -OH groups of the glycerol molecule. Because of this combination, an -OH group and -H are left, which combine to form a water molecule.

Since triacylglycerols have three fatty acids, you can get mixed-fatty-acid triacylglycerols, in which there are different fatty acids on each of the glycerol bonds. Naturally occurring soybean oil is a mixed triacylglycerol, containing saturated, monounsaturated, and polyunsaturated fatty acids. Soybean oil contains more monounsaturated and polyunsaturated fatty acids than saturated fatty acids.

Surfactant is a short term for surface-active agent. Polar lipids, like lecithin in soybean oil, serve as specialized surfactants known as emulsifiers. By interacting with water on one end of the molecule and repelling water on the other end, emulsifiers keep fat globules dispersed in water or water droplets dispersed in fat. Lipid surfactants are important to our own cellular functions, as well as useful in stabilizing specific food products. Lecithin is a phospholipid, which functions as a surfactant. Lecithin and other phospholipid emulsifiers are found in food from animal and plant sources. The food sources of lecithin are eggs, milk, cheese, and soybean oil. These chemical properties of lecithin are used in the food industry to prevent fats from separating out of chocolate, mayonnaise, peanut butter, and salad dressings.

The fats that you see in raw beef, chicken, and pork are known as visible fats. These fats are in plain view and are solid at room temperature. Vegetable oils are also visible fats. The fats that are in snack foods, cookies, desserts, and candy are known as invisible fats. Although you cannot see them, they can add extra calories to your diet.


Activity/Experiment: Download PDF Version

Activity Objective

In this experiment, we will be extracting and examining the fat in chocolate, potato chips, and sunflower seeds. In chocolate, sugar and cocoa are dispersed in a crystallized fat matrix. To keep the fat from separating out of the chocolate, an emulsifier called lecithin is used. The fat in the potato chip is mostly on the surface of the chip from the frying process. The fat in the sunflower seed is in the seed itself. The cooking oils that we use come primarily from nuts and seeds. Examples of these fat sources are corn, soybean, and peanut oils.

Materials Required

  • Chocolate chips (semi-sweet)
  • Balance or scale
  • Sunflower seeds
  • Microwave
  • Potato chips
  • Paper towels
  • Acetone
  • Foil
  • 100-mm Petri dishes
  • Hammer
  • 100-and 600-milliliter beakers
  • Safety goggles
  • Graduated cylinder
  • Latex or rubber gloves

Experimental Procedure

Part A. Visual evidence of invisible fats from foods

Part 1. Chocolate Chips

  1. Measure out 2 grams of chocolate chips and place on a paper towel.
  2. Microwave for 40 seconds on high.
  3. Fold the paper towel over the chocolate chips and gently press the chocolate chips flat with your fingers.
  4. Allow it to sit for 5 minutes. Open up the paper towel. Record your results.

Part 2. Potato Chips

  1. Measure out 2 grams of potato chips and place on a paper towel.
  2. Microwave for 25 seconds on high.
  3. Fold the paper towel over the potato chips and crush the chips with a hammer.
  4. Allow it to sit for 5 minutes. Open up the paper towel. Record your results.

Part 3. Sunflower Seeds

  1. Measure out 2 grams of sunflower seeds and place on a paper towel.
  2. Microwave for 25 seconds on high.
  3. Fold the paper towel over the sunflower seeds and crush the seeds with a hammer.
  4. Allow it to sit for 5 minutes. Open up the paper towel. Record your results.

DATA TABLE – VISUAL OBSERVATIONS OF FAT

Food Describe what you see on the paper towel
Chocolate chips  
Potato chips  
Sunflower seeds  

 

Part B. Quantitative measurement of invisible fats from foods

Part 1. Extraction of Fat from Chocolate Chips

  1. Weigh out 5 grams (9 chips) of chocolate chips. Crush the chocolate between two sheets of foil with a hammer.
  2. Label the beakers that you are using to put the food in, one each for chocolate chips, potato chips, and sunflower seeds. Record the weights of the labeled beakers.
  3. Using the beaker that is labeled for chocolate chips and place the crushed chocolate chips in the beaker. Record the weight with the crushed chocolate chips.
  4. Add 10 milliliters of acetone to the crushed chocolate chips in the beaker.
  5. Swirl for 1 minute in a hood, or stir with a glass rod (in a well ventilated area).
  6. Carefully decant the acetone into the Petri dish, making sure the chocolate remains in the beaker.
  7. Add 10 milliliters of acetone to the chocolate and repeat steps 5 and 6.
  8. Allow the acetone in the Petri dish to dry overnight in a hood (or a well ventilated area) to visualize the lipid that was extracted.
  9. Allow the beaker with the chocolate to dry overnight. Weigh the beaker with the chocolate.

 

Part 2. Extraction of Fat from Potato Chips

  1. Weigh out 5 grams of potato chips. Break into dime-size pieces with your fingers.
  2. Repeat steps 2-9 in Part 1.

Part 3. Extraction of Fat from Sunflower Seeds

  1. Weigh out 5 grams of sunflower seeds. Crush the seeds between two pieces of foil with a hammer.
  2. Repeat steps 2-9 in Part 1.

DATA TABLE – EXTRACTION OF LIPIDS

Food Weight of beaker Weight of beaker with raw food Weight of raw food Weight of beaker with dried food Weight lost from food % Lipid extraction
Chocolate chips            
Potato chips            
Sunflower seeds            

(weight of beaker with raw food) – (weight of beaker) = weight of raw food

(weight of beaker with raw food) – (weight of beaker with dried food) = weight lost from food

(weight lost from food / weight of raw food) x 100 = % lipid extracted

DATA TABLE – DESCRIPTION OF FATS

Food Color Texture Odor Viscosity
Chocolate chips        
Potato chips        
Sunflower seeds        

 

Questions

  1. How can you tell that the dark wet spot on the paper towel is fat and not water?
     
  2. Rank from most to least the percentage of lipid extracted from all three foods. Look at the Nutrition Facts label on the packages of all three foods and rank them. Did your ranking agree with the ranking of the product labels?
     
  3. Determine which lipids contained saturated and unsaturated fatty acids in this experiment, based on your descriptions of the fats in the Petri dishes.

NAME______________________________CLASS_________________PERIOD____

Freaky Fats: Download PDF Version

Solution for Freaky Fats

  1. FATTY ACIDS
  2. OILS
  3. LECITHIN
  4. ESTER BONDS
  5. SHORTENING
  6. EMULSIFIERS
  7. POLYUNSATURATED
  8. GLYCEROL
  9. ANIMAL
  10. VEGETABLE

HIDDEN MESSAGE: COCONUT OIL


NAME______________________________CLASS_________________PERIOD____

Phats: Download PDF Version

Solution to Phats

S E A T A D L P V A R T I E T

L T Y O F I A O F R U R I E T

S I E V E C T L G E T I A S B

L S P A E A S Y S A N A D T G

S R T I R C Y U A I N C S E D

O I A N D I R N I L Y Y E R +

+ R C + A E C S + + + L M B S

+ + G + + L + A + + + G U O E

+ + + A + O P T C + + L L N A

+ + + + N N + U + I + Y S D F

S T A E M I + R + + D C I + O

+ + + + + L C A + + + E F + O

S D I C A Y T T A F + R I + D

+ + + R L I O E V I L O E + +

+ + D + + + + D + + + L R + +

(Over, Down, Direction)

CIS (3, 7, NW)
CRYSTAL (7, 7, N)
EMULSIFIER (13, 6, S)
ESTER BOND (14, 2, S)
FATTY ACIDS (10, 13, W)
LARD (6, 12, SW)
LINOLEIC ACID (6, 12, N)
LIPID (1, 2, SE)
MEATS (5, 11, W)
OLIVE OIL (12, 14, W)
ORGANIC (1, 6, SE)
PLANTS (7, 9, NW)
POLYUNSATURATED (8, 1, S)
SEAFOOD (15, 7, S)
STEARIC ACID (1, 1, SE)
TRIACYLGLYCEROL (12, 1, S)

HIDDEN MESSAGE:

We should eat a variety of fruits, vegetables, and grains daily.

Continue to Unit Three


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