Lipids Flashcards
Lipid elemental composition
C H O
chemical structure/formula
CH3 (CH2)n COOH
the three classes
saturated
monounsaturated
polyunsaturated
Saturated fatty acids
each carbon has a full quota of hydrogen atoms
no double bonds between carbon atoms
solid at room temp
generally from animal sources (butyric acid butter and stearic acid steak)
Monounsaturated fatty acids
all atoms aren’t saturated with hydrogen
one double bond between carbon atoms
generally soft/liquid at room temp
generally come from plant sources (oleic acid from corn oil)
Polyunsaturated fatty acids
all carbon atoms are not saturated with hydrogen
more than one double bond
generally soft liquid at room temp
generally from plant sources (walnuts, seeds and flax oil) and fish(salmon, herring)
EXAMPLES OF POLYUNSATURATED/ESSENTIAL FATTY ACIDS: linoleic linolenic, arachidonic
essential fatty acids
can’t be manufactured in the body must be obtained through food
Linoleic is most important as others can be synthesised from it
functions of essential fatty acids
formation of cell membranes (growth)
can counteract the hardening effect of cholesterol on the arteries reducing the risk of CHD.
Omega 3 fatty acids
a particular unsaturated fatty acid with the FIRST DOUBLE BOND between the THIRD AND FOURTH carbon atoms
sources of omega 3
oily fish: salmon, sardines
nuts
seeds
soya beans
supplement
benefits of Omega3 fatty acids
reduce the risk of heart attack and stroke
improve brain function and help to fight age related mental decline (cognitive function)
improve eye health
reduce risk of certain cancers
structure of saturated fatty acid
O H H H H
|| | | | |
HO -C-C-C-C-C- H
| | | |
H H H H
structure of monounsaturated
O H H H H
|| | | | |
HO -C-C-C=C-C- H
| | | |
H H H H
structure of polyunsaturated
O H H H H
|| | | | |
HO -C-C=C-C=C- H
| |
H H
Cis fatty acid
polyunsaturated fatty acids are called cis fatty acids when the hydrogen atoms on the same side of the double bond i.e both above or below the carbon chain
Sources: sunflower and olive oil, nuts, avocados
H H | | —C = C—
Trans fatty acids
polyunsaturated fatty acids are called trans fatty acids when the hydrogen atoms are on opposite sides of the double bond
Sources: crisps, biscuits, cakes, crackers
H
| —C = C —
|
H
Significance of trans fatty acids in the diet
regarded as unhealthy and are thought to play a role in increasing the incidence of CHD
they increase LDL which deposit cholesterol on walls of the arteries
Reduce HDL which remove cholesterol from circulation
Animal lipids
meat
butter
cream
cheese
milk
egg yolk
plant lipids
nuts
but oils
vegetable oils
margarine
cereals
soya beans
marine sources
salmon
mackerel
trout
herring
sardines
tuna
fish liver oils
Properties of lipids
SOLUBILITY
Insoluble in water but soluble in solvents (alcohol)
Properties of lipids
AFFECTED BY HEAT
solid fats melt when heated to 30-40°C.
Lipids boil at extremely high temps (175-195°C)
Beyond these temperatures smoke point and eventually flash point can occur.
Properties of lipids
PLASTICITY
This property related to whether a lipid is solid, liquid or spreadable.
It’s determined by the degree of saturation.
The more saturated fatty acids are present, the more solid the lipid.
As a result, many unsaturated margarines are spreadable and suitable for creaming.
Properties of lipids
RANCIDITY: Ocidative
the spoilage of lipids
more common
occurs when oxygen combines with carbon atom at the double bond
results in rancid smell and taste
aided by light
Properties of lipids
RANCIDITY: Hydrolytic rancidity
occurs when enzymes and bacteria hydrolyse lipids changing them to fatty acids and glycerol
results in unpleasant smell and taste
can occur in freezer due to enzymes
to prevent oxidative rancidity
store in cool dark place
wrap well
Antioxidants added during production prevent oxidative rancidity by combining with the oxygen making it unavailable to attach to the carbon atom
Properties of lipids
HYDROGENATION
an unsaturated fatty acid can have hydrogen added in the presence of a NICKEL CATALYST, converting oil into fats.
It is used in the production of margarine
Properties of lipids
EMULSIFICATION: water in oil
water droplets are dispersed in oil
eg: butter, margarine
Properties of lipids
EMULSIFICATION: oil in water
oil droplets are dispersed in water
eg: milk, mayonnaise
temporary emulsions
formed by vigorous shaking
eg: oil and vinegar in a vinaigrette dressing
permanent emulsions
formed with the help of an emulsifier Eg: lecithin in egg yolk acts as an emulsifier in mayonnaise preventing the water in the eggs and vinegar form separating from the oil
maintaining emulsions
emulsifier/ emulsifying agents
an emulsifier is a molecule that has a hydrophilic head an a hydrophobic tail.
The hydrophilic head attaches itself to the water molecule and the hydrophobic tail attaches itself to the oil molecule, preventing them from separating
Eg: lecithin in egg yolks
maintaining emulsions
stabiliser
maintain emulsion, preventing separation
eg: pectin, gelatine
Melting point
30-40°C
boiling point
175-195°C
Smoke point
fats and oils start to decompose if overheated
The glycerol separates from the fatty acid la and changes to ACROLEIN, producing a blue haze (vapour) or smoke while emitting an acrid smell.
It occurs at 200°C for fats
And 250°C for oils
Smoke point is lowered if lipids contain impurities such as food particles
flash point
extreme overheating causes the vapour to spontaneously ignite
occurs at 310 for fats
325 for oils
Biological functions of lipids
supply body with heat and are a concentrated source of energy
Excess is stored as adipose tissue, insulating the body and acting as an energy reserve
Protect delicate organs such as kidney and insulate nerve fibres
Source of essential fatty acids
To reduce fat in diet
Buy lean cuts of meat and remove fat
choose low fat cooking method (grilling, steaming or baking) instead of frying
use low fat spreads and low fat varieties of milk and yogurt
avoid hidden fats in snacks such as crisps and pastries
INCRWASE CONSUMPTION OF HIGH FIBRE FOODS SUCH AS FRUIT VEG AND WHOLEGRAINS AND DECREASE PORTION SIZE OF CHEESE MEAT
DIGESTION
PACREAS
Secretion: pancreatic juice
Enzyme: Lipase
Substrate: lipid
Product: fatty acid and glycerol
DIGESTION
LIVER
Secretion: bile
Enzyme:—
Substrate: lipids
Product: EMULSIFIED LIPID
DIGESTION
SMALL INTESTINE
Secretion: intestinal juice
Enzyme: lipase
Substrate: lipid
Product: fatty acids and glycerol
Absorption and utilisation
digested lipids are oxidised in muscles and liver and are used:
to produce heat and energy
in formation of cell membranes
excess is stored as adipose tissue
