Lipids Flashcards
What are lipids
Fats in foods - otherwise known as triglycerides
Intro to lipids
Fats and oils - lipids
Composed of carbon, hydrogen and oxygen
Physical appearance different at room temp :- fats are solid, oils are liquid
Fats are insoluble in water
Fats are found in Both plant and animal sources.
Main functions of fat
Provides concentrated source of energy
1g of pure fat provides 37 kj ( 9cal)
More energy that the same weight of csrbohydrate or protein.
By supplying energy, fats save protein from being used for energy - called protein sparing.
Use - Formation of body fat (adipose tissue)
Acts as an energy store
Adipose tissue is an insulating layer beneath the skin to help preserve body heat. It cushions and insulates us from the cold
Use - protects organs
Fat surrounds our vital organs such as kidneys to help protect them
Use - fat soluble vitamins
Fat provides a source of fat soluble vitamins ADEK. These are stored in the adipose tissue and liver.
Fat is an essential component of all cell membranes in the icy.
Fat delays gastric emptying , and fatty foods take longer to digest that other nutrients. This can prevent prevent hunger sensations for longer so a person feels satiated for a longer period of time.
Some fats supply the essential fatty acids:
- linoleic acid ( omega 7)
- alpha linoleic acid ( omega 3)
Triglycerides
Made up of three fatty acids attached to 1 glycerol backbone .
Triglycerides info
- account for 95% of the fat in our diet
- fat belongs to a group of substances called esters
- they’re formed from the combination of glycerol ( and alcohol) and three fatty acid molecules ( organic acid)
- there are 4 molecules for each fat molecule
- these three fatty acid molecules are often different ( mixed triglycerides ) and these fatty ASICS define the type of fat.
Glycerol
H h h
H c c c h
Oh oh oh
Fatty acid general formula
O
//
C - r
|
Oh
Condensation reaction
Different combinations of fatty acids combine with glycerol to form a wide variety of fat molecules.
Three fatty acids combine with glycerol by condensation reaction s to form a triglyceride.
Saturated fats
A saturated fatty acid has the maximum possible number of hydrogen atoms attached to every carbon.
It is therefore said to be saturated with hydrogen and all the carbons are attached to each other with single bonds.
They have no c = c double bonds in their chain.
Unsaturated fat
Some fatty acids have a pair of hydrogen atoms in the middle of a chain that are missing and create a gap.
This leaves two carbon atoms connected by a double bond rather than a single bond.
Unsaturated fats do have a c v c double bond in the chain
If there are more than one double bond then the fat is said to be polyunsaturated.
Difference between saturated and unsaturated fats.
Most saturated come from animal sources - meat, pastry, butter, hard cheese, lard.
Different types of saturated fatty acids:
- butyric acid - butter and milk
- palmitic acid - animal fats
- Laurie acid - daisy and coconut oil
Stearic acid - beef fat
Most unsaturated fats come from. Plant sources e.g. avocados, nuts, seeds, soya, beans, olive oil. Exception is oily fish.
Double bond gives special properties. They have a bend or curve in the otherwise straight carbon chain. This I
Allows molecules more movement and why unsaturated fats are liquid at room temperature.
Fats and health
Saturated fats increase low density lipoprotein (ldl)
High ldl cholesterol is a risk factor for chd, heart attacks, angina and strokes.
Unsaturated fats have been shown to lower ldl cholesterol and increase hdl cholesterol which helps to protect against heart disease.
Recommendations on fat
Total fat should contribute no more than. 35% to diet. 11% of food energy Fat should come from saturated fatty acids.
Average total fat intake of uk adult is now 34.6%.
Intakes of saturated fat are too high : avg intake for men and women = 12.8% And 12.6% of food energy.
Recommendations on fat
Total fat should contribute no more than. 35% to diet. 11% of food energy Fat should come from saturated fatty acids.
Average total fat intake of uk adult is now 34.6%.
Intakes of saturated fat are too high : avg intake for men and women = 12.8% And 12.6% of food energy.
Trans fats
Chemical structure of unsaturated fats, hydrogen atoms are on the same side of a double bond. Referred to as a ‘CIS’
Trans fats are formed artificially and have hydrogen atoms on geometrically opposite sides of double bond. Fats are flipped
Trans fats are formed via a process called hydrogenation.
Many countries are phasing their usage out including America.
Hydrogenation
Hydrogen gas is added under pressure in the form of tiny bubbles at the base of the agitator.
Nickel catalyst is added in an oil slurry
Hydrogenation ( hardening) changes a liquid oil into a solid fat by adding hydrogen across the double bonds in the unsaturated fatty acid molecules. Improving shelf life of the fat and helping to reduce oxidation
Essential fatty acids
Some fatty acids cannot be made by the body and must come from food.
Examples are;
- butyric acid - saturated, found in butter
- Lauric acid - saturated , found in palm oil
Oleic ackd - monounsaturated, found in olive oil, nuts
Linoleic acid - acid - polyunsaturated, found in flax seeds, and sesame seeds
Too little EFA’s
Fatigue
Lack of endurance
Dry skin
High blood pressure
Angina
Aching
Frequency colds
Properties of fats - melting points
- Saturated fats have straight molecules as there are only single bonds. These can pack together tightly. The closeness means they bond together tightly, and more energy is needed to separate them. They have higher melting points and tend to be solids
- Unsaturated fats have less straight molecules as the double bond gives them a kink. These pack together less tightly. Less closeness means they don’t bind together so tightly p, and less energy is needed to separate them.
Properties of fats - solubility
Fats and oils are insoluble in water
When you use an emulsifying agent, you can form a stable mixture of fat and water - emulsion.
The emulsion may be a fat in water emulsion e.g. milk or a water in fat emulsion e.g. butter
- fats and oils are soluble in organic solvent such as petrol and carbon tetrachloride
- solvents of this type can be used to remove grease and stains from clothing.
Properties of fats - plasticity
- fats do not melt at fixed temps , but at range of temps
- this because fats are mixtures of triglycerides, all with diff. Melting points.
Some of the fatty acids forming the triglycerides will stay solid for longer than others.
% feature gives fat its plasticity that makes some fats spreadable. - e.g. margarine - has a wide range of plasticity and will spread from the fridge whereas ,most animal fat will have narrow plasticity and will not spread easily.
Properties of fats - smoke points
When a fat or oil is heated to a certain temperature it starts to decompose, producing a blue haze or smoke.
Most fats and oils start to smoke at 200degrees. Smoke point for lard = 185gegrees
Corn oil = 232degrees.
In general, vegetable oils have a higher temperature than animal fats.
Properties of fats - saponification
The name saponification literally mean soap making
A chemical reaction. That occurs when a vegetable oil or animal fat (triglyceride ) is mixed with a strong alkali.
