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AP Biology
Lipids: Fats & Oils
AP Biology 2006-2007
Lipids
AP Biology
Lipids Lipids are composed of C, H, O
are esters of long-chain fatty acids and alcohols
Diverse group fats Fixed oils Waxes
AP Biology
Fat and Fixed oil Structure:
glycerol (3C alcohol) + fatty acid
dehydration synthesis
fatty acid = long HC “tail” with COOH group at “head”
enzyme
AP Biology
Building Fats Triacylglycerol
3 fatty acids linked to glycerol ester linkage = between OH & COOH
AP Biology
Dehydration synthesis
enzyme
enzyme
enzyme
dehydration synthesis
AP Biology
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.
AP Biology
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
AP Biology
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
AP Biology
Saturated vs. unsaturatedsaturated unsaturated
AP Biology
Chemical constants
i. Acid Values
ii. Saponification Value
iii. Ester Value
iv. Iodine Value
v. Unsaponifiable Matter
AP Biology
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.
AP Biology
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).
AP Biology
ESTER VALUE Ester value: The difference between
the saponification and acid values.
AP Biology
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
AP Biology
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.
AP Biology
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).
AP Biology
SIGNIFICANCE?These constants are important general
tests to ensure - That the oil is genuine- To detect adulteration of fixed oils and
fats.
AP Biology
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
AP Biology
Examples of valuable fixed oils:
i. Olive oil
ii. Cod-liver oil
AP Biology
OLIVE OIL
Olive oil is the oil expressed
from the ripe fruits of Olea
europea (Oleaceae Family).
AP Biology
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.
AP Biology
OLIVE OIL: CHARACTERISTICS
Olive oil: Pale yellow liquid, sometimes with a green tint.
Oil has a slight odour & nice taste.
AP Biology
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.
AP Biology
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.
AP Biology
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
AP Biology
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.
AP Biology
COLLECTION & EXTRACTIONCod-livers (contain 50% oil), are removed
immediately after the fish are caught & transferred to steamers & stored at low temperature.
AP Biology
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.
AP Biology
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.
AP Biology
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.
AP Biology
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
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