Transcript Lipids Dr ghada

Lipids: Fats & Oils
AP Biology
Lipids
AP Biology
2006-2007
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
 fatty acid =
long HC “tail” with COOH group at “head”
enzyme
dehydration synthesis
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Building Fats
 Triacylglycerol
3 fatty acids linked to glycerol
 ester linkage = between OH & COOH

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Dehydration synthesis
dehydration synthesis
enzyme
enzyme
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enzyme
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 double
bonded C prevent the
molecules from packing
tightly together
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Saturated vs. unsaturated
saturated
unsaturated
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Chemical constants
i.
ii.
iii.
iv.
v.
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Acid Values
Saponification Value
Ester Value
Iodine Value
Unsaponifiable Matter
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 VALUE
Iodine 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 & EXTRACTION
Cod-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 OIL
Cod-liver oil should
be stored in wellfitted 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 & USES
The 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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