lipids Flashcards
what is the elemental composition of lipids
oxygen, hydrogen, carbon
what is the structure of saturated fatty acids
-each carbon atom is fully saturated with its full quota of hydrogen atoms
-no double bonds occur between the carbon atoms
what is the consistency and melting point of saturated fatty acids
-solid at room temperature (18C)
-high melting point
what are the sources of saturated fatty acids and give examples
-generally found in animal sources
-e.g. butyric acid in butter and stearic acid in meat
what is the structure of monounsaturated fatty acids
-each carbon is not fully saturated with a full quota of hydrogen atoms
-there is one double bond between the carbon atoms
what is the consistency and melting point of monounsaturated fatty acids
-soft or liquid at room temperature (18C)
-low melting point
what are the sources of monounsaturated fatty acids and give examples
-generally found in plant and marine sources
-e.g. oleic acid in olive oil
what is the structure of polyunsaturated fatty acids
-each carbon atom is not fully saturated with a full quota of hydrogen atoms
-there is more than one double bond between the carbon atoms
what is the consistency and melting point of polyunsaturated fatty acids
-soft or liquid at room temperature (18C)
-lowest melting point of all the fatty acids
what are the sources of polyunsaturated fatty acids and give examples
-generally found in plant and marine sources
-e.g. linoleic acid in nuts and linolenic acid in seeds
what are essential fatty acids
essential fatty acids are acids that cannot be manufactured by the body and therefore must be obtained from food
what are the sources of essential fatty acids
-nuts
-seeds
-olive oil
-oily fish
what are the biological functions of essential fatty acids
-aid cell membrane formation, which is essential for growth
-reduce the risk of coronary heart disease by raising high-density lipoprotein which helps remove cholesterol from the blood and by lowering low-density lipoprotein which deposits cholesterol in the blood
describe the structure of an omega-3 fatty acids
omega-3 fatty acids have a double bond between the third and fourth carbon atoms along their hydrogen chain
what are the sources of omega-3 fatty acids
-oily fish
-seeds
-nuts
-fish oils
what are the biological functions of omega-3 fatty acids
-reduce the risk of coronary heart disease, heart attacks and strokes by raising HDL and lowering LDL
-decrease the viscosity of blood, preventing clots or blockages in the coronary arteries
-aid foetal brain development during pregnancy as well as helping to improve memory and cognitive functioning throughout life
what is the chemical structure of cis fatty aids
the hydrogen atoms on either side of the double bond are both above or both below the carbon chain
what are the sources of cis fatty acids
naturally occurring in foods such as olive oil and oily fish
what is the significance of cis fatty acids in the diet
generally good for health as they raise HDL while lowering LDL decreasing the risk of coronary heart disease
what is the structure of trans fatty acids
the hydrogen atoms on either side of the double bond are on opposite sides of the carbon chain
what are the sources of trans fatty acids
-the heating or frying of oils at high temperatures
-pastries and crisps
what is the significance of trans fatty acids in the diet
generally bad for health as they lower HDL while raising LDL increasing the risk of coronary heart disease
what are the properties of lipids
-solubility
-absorption of flavours
-emulsions
-hydrogenation
-rancidity
-plasticity
explain solubility as a property of lipid
lipids are insoluble in water. they are soluble in solvents such as ether and benzene
explain absorption of flavours as a property of lipid
lipids absorb flavours easily, e.g. chilli oil
explain heating lipids as a property of lipid
melting point: solid fats melt when heated to 30-40C
smoke point: if lipids are heated to 200C or 250C they begin to decompose causing the glycerol to separate from the fatty acids. glycerol is then broken down into acrolein and produces a blue smoke or haze and a harsh smell
-flash point: extreme overheating of lipids to 310C and 325C causes vapour to be released that can spontaneously catch on fire
explain emulsion as a property of lipid
an emulsion is a colloidal solution, formed when two immiscible liquids are forced to mix together. emulsion can be described as water in oil emulsions or oil in water emulsion
what is water in oil emulsion
e.g. butter, margarine. tiny droplets of water are dispersed throughout oil or fat
what is oil in water emulsion
e.g. milk, mayonnaise. tiny droplets of oil are dispersed throughout the water
what is temporary emulsion
formed when the two immiscible liquids, e.g. vinegar and oil are in vinaigrette, are shaken vigorously. if left to stand they will seperate
what is permanent emulsion
formed when an emulsifier is added to two immiscible liquids, preventing them from separating, e.g. vinegar and oil in mayonnaise
what is emuslifiers
are molecules that have a hydrophilic (water-loving) head and a hydrophobic (water-hating) tail. when an emulsifier is added to a mixture of two immiscible liquids the hydrophilic head attaches itself to the water and the hydrophobic tail attaches itself to the oil. this prevents the liquids from separating, creating a permanent emulsion
what is a stabilisers
are long-chained molecules that helps to maintain emulsions by separating the oil droplets and preventing them from coalescing
explain hydrogenation as a property of lipid
is a process whereby hydrogen gas, in the presence of a nickel catalyst is forced through the double bond of an unsaturated oil, converting the unsaturated oil into a saturated solid fat, e.g. used in the production of margarine
explain rancidity as a property of lipid
is the spoilage or decomposition. this results in an unpleasant odour and taste. there are two types of rancidity: oxidative and hydrolytic rancidity
what is oxidative rancidity
occurs when oxygen in the air combines with the carbons in a double bond of the unsaturated fatty acid
what is hydrolytic rancidity
occurs when enzymes or bacteria break down lipids into glycerol and fatty acids
explain plasticity as a property of lipid
describes how soft, flexible and shapable a fat is at a given temperature. it is determined by the degree of saturation, the more saturated fatty acids present, the more solid the lipid
what is the biological functions of lipids
-lipids supply the body with heat and energy, helping to keep the body temperature at 37C and providing energy for all activities
-lipids form a protective layer that surrounds delicate organs, e.g. the kidneys
-lipids supply the body with the fat-soluble vitamins A,D,E and K which are necessary for overall health
-excess lipid intake is stored as adipose tissue under the skin. this insulates the body and acts as an energy reserve
