Lab 4 Free fatty acids Lipid peroxide, and TBARS

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Lab 4 Free fatty acidsLipid peroxide, and TBARS
Objectives

• Have a clear understanding of the chemistry
• Be able to accurately carry out the experiment
  and report data

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Triglyceride
Acid
lipase
Free fatty acid
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Where FFA come from ?

• Lipase in oil seeds
• Acid hydrolysis during extraction and refining
• Lipid oxidation during storage
• Peroxide ? aldehyde ? acid

High FFA poor quality
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Analyze Free Fatty Acids

• Similar to a TA. Dealing with an oil sample makes
  analysis more difficult, and some oils are
  colored. pH meters and oil dont get along very
  well, so you must use an indicator and try your
  best.
• Sample dissolved in hot ethanol and titrated
  until the fatty acids are neutralized (pH 8.2).

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Lipid oxidation
Primary products Peroxide
Secondary products malonaldehyde
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Lipid oxidation
malonaldehyde
Peroxides
Time
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Analyze the peroxide
Peroxides oxidize I- to iodine
In 1 L solution
2 I- H2O ROOH ? ROH 2OH- I2
1 eq
1 eq
1 eq
1 mol
0.5 mol
0.5 mol
Iodine and starch form complex of blue color
Iodine is consumed by sodium thiosulfate
2S2O32- I2 ? S4O62- 2 I-
1 eq
1 eq
1 eq
1 mol
1 mol
0.5 mol
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Step-by-step

• Oil is dissolved in chloroform-acetic acid and KI
  added to the mixture, water is then added.
• PV is determined by measuring the amount of
  iodine liberated
• Na2S2O3 is use the determine the liberated
  iodine
• A solution of starch is added, which turns blue
  in the presence of iodine, to help with the last
  stages of the titration.
• Disappearing of blue color indicates the end
  points. The solution become clear liquid

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PV of Fats and Oils

• PV milliequivalents of peroxide per kilogram of
  oilor mEq/Kg
• Equal equivalent of compounds react with each
  other in a reaction
• milliequivalents of peroxide milliequivalents
  of Na2S2O3

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Thiobarbituric acid
malondialdehyde
Heat
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• Not specific to malonaldehyde, results sometimes
  are reported as ThioBarbituric Acid Reactive
  Substances (TBARS).

Malonaldehyde bis(diethyl acetal) (MBA)
1 mol of MBA 1 mol of Malonaldehyde
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Safety

• How to heat ethanol?
• Is chloroform flammable?
• How chloroform is absorbed ?
• What kind of glove should be used ?
• When will it cause cancer ?