AP Biology

Lipids: Fats & Oils

AP Biology 2006-2007

Lipids

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Lipids Lipids are composed of C, H, O

are esters of long-chain fatty acids and alcohols

Diverse group fats Fixed oils Waxes

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Fat and Fixed oil Structure:

glycerol (3C alcohol) + fatty acid

dehydration synthesis

fatty acid = long HC “tail” with COOH group at “head”

enzyme

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Building Fats Triacylglycerol

3 fatty acids linked to glycerol ester linkage = between OH & COOH

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Dehydration synthesis

enzyme

enzyme

enzyme

dehydration synthesis

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Structure of Fatty Acids

The “tail” of a fatty acid is a long hydrocarbon chain, making it hydrophobic. The “head” of the molecule is a carboxyl group which is hydrophilic. Fatty acids are the main component of soap, where their tails are soluble in oily dirt and their heads are soluble in water to emulsify and wash away the oily dirt. However, when the head end is attached to glycerol to form a fat, that whole molecule is hydrophobic.

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Saturated fats All C bonded to H No C=C double bonds

long, straight chain most animal fats solid at room temp.

contributes to cardiovascular disease (atherosclerosis) = plaque deposits

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Unsaturated fats C=C double bonds in

the fatty acids plant & fish fats vegetable oils liquid at room temperature

The doublebonded C prevent the molecules from packing tightly together

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Saturated vs. unsaturatedsaturated unsaturated

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Chemical constants

i. Acid Values

ii. Saponification Value

iii. Ester Value

iv. Iodine Value

v. Unsaponifiable Matter

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ACID VALUE

Refers to the number of mg of KOH needed to neutralize the free acids in 1 g of oil.

-High acid values occur in oils which are rancid.

- Pharmaceutical oil must not have any acidity.

Significance

Acid value is the measure of hydrolytic rancidity. In general, it gives an indication about edibility of the lipid.

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SAPONIFICATION VALUE

The hydrolysis reaction of lipids (with KOH

above) can be used to determine the

saponification value of the oil.

Saponification value is expressed as the

number of mg of KOH needed to neutralize the

free acids in, and to hydrolyse the esters in, 1

g of the substance (oil).

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ESTER VALUE Ester value: The difference between

the saponification and acid values.

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IODINE VALUEIodine value:

Gives the measurement of the unsaturation of the oil. The higher the iodine number, the more unsaturated fatty acid bonds are present in a fat.

Ex. linseed oil

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UNSAPONIFIABLE MATTER

The fraction of substances in oil & fat which is

not saponified by caustic alkali, but is soluble in

ordinary fat solvent is called unsaponifiable

matter.

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UNSAPONIFIABLE MATTER Unsaponifiable matter

consists of compounds such as sterols, which remain after saponification of the triglycerides and the removal of the glycerol and soaps (by using solvents).

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SIGNIFICANCE?These constants are important general

tests to ensure - That the oil is genuine- To detect adulteration of fixed oils and

fats.

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ADULTERATION OF FIXED OILS

-Cheap oils are often mixed

with more expensive oils

as a form of adulteration.

-Three of the most

commonly used oils are:

Sesame oil

Cotton seed oil

Arachis oil

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Examples of valuable fixed oils:

i. Olive oil

ii. Cod-liver oil

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OLIVE OIL

Olive oil is the oil expressed

from the ripe fruits of Olea

europea (Oleaceae Family).

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OLIVE OIL 1st oil expressed: Virgin oil Subsequent extractions:

marc is solvent extracted – lower quality oil.

Superior grades of oil: Extra-virgin, Virgin, or Refined.

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OLIVE OIL: CHARACTERISTICS

Olive oil: Pale yellow liquid, sometimes with a green tint.

Oil has a slight odour & nice taste.

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OLIVE OIL: CONSTANTS If the fruits used to produce the oil have been

allowed to ferment, the acid value will be higher than is officially permitted.

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OLIVE OIL: CONSTITUENTS Oils from different sources differ

slightly in their constituents (composition).

This result may be due to the different varieties of olive used, or to climate differences.

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Type I Type II BP Limits _______________________ % % %_________________________________________

Oleic Acid 78-86 65-70 56-85

Linoleic Acid 0-7 10-15 3.5-20

Palmitic Acid 9-12 15 7.5-20

Stearic Acid 9-12 15 0.5-5.0

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COD-LIVER OIL

DEFINITION:

Medicinal cod-liver oil is a fixed oil prepared from the fresh liver of the cod, Gadus callarias, & other Gadus spp. (Gadidae Family), under conditions which make it palatable & containing a certain amount of Vitamins.

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COLLECTION & EXTRACTIONCod-livers (contain 50% oil), are removed

immediately after the fish are caught & transferred to steamers & stored at low temperature.

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STORAGE OF COD-LIVER OILCod-liver oil should be stored in well-

fitted airtight containers.

It should be protected from light & stored in a cool, dry place.

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Rancid oils are a major source of destructive free radicals in our diet. Exposure to air, heat, and light cause oils to oxidize, become rancid, and form free radicals.

Monounsaturated fats, since they have a pair of missing hydrogen atoms are somewhat vulnerable to oxidation. Polyunsaturated oils, which are missing several pairs of hydrogen atoms, are very unstable and highly reactive to oxidation.

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COD-LIVER OIL: CONSTITUENTS

The oil consists of glycerides of unsaturated (85%) and saturated (15%) acids.

Saturated fatty acids: myristic acid, palmitic acid & traces of stearic acid.

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ACTIONS & USESThe medicinal properties of

cod-liver oil are mainly due to the Vitamins A & D.

It is widely used in underdeveloped countries for the prevention & treatment of rickets.

Europe & USA: Traditionally

used as a vitamin supplement.Recent research: relief of rheumatic pains & joint & muscle stiffness.Reduces blood cholesterol.Protects against CVD