CHM 1040 - Peanut Oil and Iodine Number

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  • 7/30/2019 CHM 1040 - Peanut Oil and Iodine Number

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    CHM 1040

    Peanut Oil Extraction and Iodine Numbers of Lipids

    Introduction

    Lipids include any substance isolated from living tissue that are soluble in nonpolar, organic

    solvents. All cells use lipids to make up the foundational structure ofcell membranes. Other lipids, like

    steroid hormones and prostaglandins function as chemical signals. The lipids most familiar to us are

    called fats and oils, which are triglycerides composed of three fatty acids in an ester linkage to glycerol.

    They function as energy reserves in both plants and animals. The fatty acids contained in thetriglycerides yield 9 calories per gram upon oxidation. Fats are solids at room temperature and generally

    found in animal sources. Oils are liquid because the fatty acids found in plants have a higher degree of

    unsaturation, that is, more carbon-carbon double bonds, than the fatty acids synthesized by animal

    cells. Shortening is also a solid because the vegetable oil present has been partially hydrogenated. This

    means that some of the C=C double bonds have reacted with H2 to become C-C single bonds. The more

    double bonds that react the more solid the partially hydrogenated vegetable oil becomes.

    Like H2, Iodine (I2) can react with carbon-carbon double bonds according to the following:

    If a triglyceride has many C=C double bonds (a higher degree of unsaturation) it will react with a lot of I2.

    From this reaction you can obtain the iodine number (I2#), that indicates the degree of unsaturation of

    triglycerides. You will use bromine, Br2, (~ 0.5% solution in acetic acid) instead of I2 because it reacts

    better. In this lab you will measure the iodine number of butter, and the peanut oil you will isolate from

    peanuts. You will do this by adding the Bromine solution drop-wise into the dissolved oil. You can tell

    when all of the double bonds have reacted because bromine has a characteristic color while the reacted

    bromine-triglyceride is colorless. The endpoint occurs when the solution turns noticeably more yellow.

    Peanuts are a very balanced food. The kernel is composed of 50% lipid (triglycerides), 3% water,

    26% protein, 19% carbohydrate, and about 2% inorganic salts including calcium and iron. It alsocontains significant amounts of the following vitamins: thiamine, riboflavin, and niacin. The primary

    fatty acids found in the triglycerides are oleic and linoleic with smaller amounts of palmitic and stearic

    acid. Its iodine number is between 83 and 98 which is more saturated than corn or soybean oil but still

    unsaturated enough to be a liquid at room temperature.

    Since only the lipid component is nonpolar, peanut oil can be extracted from ground peanuts

    using an organic solvent, in todays lab hexane. Since hexane has a lower boiling point than peanut oil,

    we can remove the solvent by heating the extracted mixture.

    C C

    H

    H

    H

    H

    + I2 C C

    H

    H

    H

    H

    H

    H

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    Procedure

    Peanut Oil Extraction

    1. Shell two large peanuts.

    2. Grind the kernels in the mortar until you have a peanut butter-like consistency.

    3. Pour 10mL of hexane into your graduated cylinder. Add approximately 8 mL of the hexane into

    the mortar with the ground peanuts. Continue to grind for a few more minutes.

    4. Set up your filter paper (folded into 16 segments) in a funnel. Place your evaporating dish

    beneath the funnel to collect the filtrate. Pour the hexane/peanut mixture into your filter

    paper. Try to scrape out any peanut solids that remain into your filter as well. After the surface ofthe peanut solids in the filter paper is almost dry add the remaining hexane.

    5. Place the filter paper with the kernel onto a paper towel in the hood to dry.

    6. Place the evaporating dish with the peanut oil - hexane solution on a hot plate in the hood.

    Heat to boiling. When the hexane bubbles are no longer forming use insulated tongs or

    hot-pads to remove the evaporating dish from the hotplate.

    7. Measure the Iodine Number of the peanut oil.

    Iodine Number Titrations

    1. Weigh 0.10 g of peanut oil or 1 cube of butter (0.2 0.4 g) in a 50 mL beaker. Record the

    weight.

    2. Add 4 mL of nonpolar solvent (50% isopropanol & 50% hexane) and mix until the

    lipid is dissolved.

    3. Add the Bromine solution dropwise into the lipid solution. Count the number of drops

    added. The endpoint occurs when a uniform yellow color persists in the flask for at least 30

    seconds. Determine the total volume of Br2 solution added (multiply the # of drops by

    1mL/45 drops).

    4. Calculate the iodine number. The equivalency factor (ef) should be on the board.

    5. Repeat steps 1 - 4 above with the other lipid.

    6. Discard all solutions containing organic solvent into the designated waste container.

    Solubility

    1. Prepare a hot water bath.2. Add water to two test tubes until 1/4 full.3. Add a pea-sized amount of palmitic acid to one tube.4. Pour the other tube into your evaporating dish containing the remainder of your peanut oil.

    (make sure youve already done the I2 test with 0.10 grams). Mix in the dish and pour the contents

    back into the test-tube.

    5. Observe both test-tubes. Did the lipid dissolve? Heat each tube for about 1 minute and note anychanges. Remember to distinguish between melting and dissolving.

    6. Cool back to room temperature. This will occur quicker if you place the test-tube in a beaker of tapwater.

    7. Add a small amount of detergent (SDS) (also about a pea-sized amount) to the palmitic acid tube.Heat, mix, and cool. Is the clump of solid palmitic acid still noticeable? Is it the same size? Where did

    the rest of it go?

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    Name ________________________________

    Results

    Lipid grams of

    Lipid

    # drops Br2 vol Br2 I2 #

    butterpeanut oil

    I2 # = grams of iodine that will react with 100g of lipid.

    I2 # =vol. Br2 soln ef 1.59 100

    grams lipid

    vol. Br2 soln. = # drops Br2 x 1.0mL/45 drops (approximately 1 - 2 mL)

    ef = equivalency factor (see board) = g Br2 per mL Br soln.

    1.59 = (MW Br2)/(MW I2) = 127/80 - corrects for use of Br2 vs. I2.100/(grams lipid) - adjusts to "per 100 grams" of lipid.

    Solubility Observations:

    Before Heating Did either the peanut oil or palmitic acid dissolve?

    After heating - Did either the peanut oil or palmitic acid dissolve? What did the palmitic acid do?

    SDS addition - Is the palmitic acid still visible after heating and then cooling? Where did it go?

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    1. Why does butter have the lowest iodine number? Is this good or bad as far as nutritional value is

    concerned?

    2. What does it mean to partially hydrogenate a vegetable oil? Based on your results for butter and

    peanut oil, would you expect the iodine # of shortening to be .....

    Less than butter between butter and vegetable oil greater than vegetable oil

    3. Classify the following as polar, nonpolar, both (note ionic = polar).

    Vegetable oil

    Soap

    Palmitic acid

    Water

    Inside of micelle

    4. Circle each of the following structures that Br2 reacts with.

    5. Classify the following as solid or liquid at room temperature.

    The salt of a fatty acid (soap)

    Palmitic acidPlant triglycerides

    Saturated fats

    O

    OH

    C C

    H

    H

    H

    H

    H

    HC C

    H

    H

    H

    H

    O

    OH

    C

    O

    H H