Fats and Lipids

• Fats and oils, also known as lipids, are like carbohydrates in that they contain the elements carbon hydrogen and oxygen.
• They provided a convenient and concentrated source of energy.
• 1g of pure fat provides 37KJ (9kcal).
• More energy than the same weight of carbohydrate or protein.
• It Surrounds and protects certain vital organs.
• Forms an insulating layer (adipose tissue) beneath the skin to help preserve body heat and protect the skeleton and organs.
• Source of fat-soluble vitamins A, D, E and K.
• Provides a reserve of energy for long-term storage.
• Provides texture and flavour to food, making more palatable and increasing feeling of ‘fullness’.
• Fats are composed of fatty acids and glycerol. 
• A fatty acid is made up of a chain of carbon atoms, with a methyl group at one end and an acid group at the other.
• Each atom in between has either one or two hydrogen atoms attached.

•   At one end of the carbon chain is the acid group which is able to combine with the glycerol.
• Three fatty acids combine with one molecule of glycerol to form a triglyceride.
• 99% of fat found in food is made up of triglycerides.

• If the fatty acid has all the hydrogen atoms it can hold it is said to be saturated.
• All of the carbon is loaded with Hydrogen – completely saturated.
• Predominantly solid at room temperature.
• The double bond at the acid end is not counted!
• The nature of the fat depends upon the types of fatty acids which make up the triglycerides.
• All fats contain both saturated and unsaturated fatty acids but are usually described as ‘saturated’ or ‘unsaturated’ according to the proportions of fatty acids present. 
• For example butter is often described as a ‘saturated’ fat because it has more saturated fatty acids than unsaturated fatty acids,
• while most vegetable oils are described as ‘unsaturated’ as they have more monounsaturated or polyunsaturated fatty acids.
• Examples: Stearic Acid – beef fat, Butyric Acid – milk, butter, Lauric Acid – dairy foods, coconut oil

• If however some of the hydrogen atoms are missing and have been replaced by a double bond between the carbon atoms, then the fatty acid is said to be unsaturated.
• Not all of the carbon atoms are loaded with hydrogen.
• Instead, there will be a double bond. 
• Oleic Acid has one double bond so it is a mono-unsaturated fatty acid.
• Can be Monounsaturated or Polyunsaturated. 
• Monounsaturated – have one double bond, and found in most animal and plant fats and oils. MUFA. 
• Polyunsaturated – have more than one double bond, and found mainly in vegetable oils. PUFA.
• Most ‘unsaturated fats’ are liquid at room temperature, are usually of vegetable origin and are commonly known as oils.  
• Vegetable and fish oils can be ‘hardened’ by a process which adds hydrogen atoms to some of the double bonds in the unsaturated fatty acids.  

• This process is known as ‘hydrogenation’. 
•  Hydrogenated vegetable oils are occasionally used in the manufacture of margarine and cooking fats, which may be used to produce cakes, biscuits and other bakery products.
• If there is one double bond the fatty acid is known as a monounsaturated fatty acid.
• If there is more than one double bond then the fatty acid is known as a polyunsaturated fatty acid. 

• All animal derived fats are saturated
•  Nearly all plant derived fats are unsaturated
•   Exceptions – palm oil and coconut oil
•   Food fats are a mixture of saturated and unsaturated fatty acids

Vegetable Oils:

• 70% of all oils in the world are vegetable oils.
• It increases the polyunsaturated fatty acids (PUFA).

·         Margarine:

• An emulsion of water and fat.
• The vegetable fat being used is first hydrogenated to give it some hardness (plasticity), and is then blended with skimmed sour milk, salt, colouring and Vitamins A and D (added by law).
• Hard margarines are more hydrogenated then soft ones.

·         Spreads and Low Fat Spreads:

• Less than 80% fat.
• High water content – not very suitable for cooking.

        Cooking fats and Shortening:

• First produced in USA as a substitute for lard and are pure fat products rather than emulsions.
• Blended with fish oils, animal fats and are ‘hydrogenated’.
• These fats are called High Ratio Fats and are designed for recipes e.g. Muffins

·         Lard 

• Extracted from pigs via heating OR ‘rendering’.  
• Almost 100% fat

·         Butter

• Churning of pasteurised cream, this causes the cream to become more viscous forming a solid butter.
• Colour and salt is added to butter and is mixed for desired consistency.

          Suet

• Fat from around the kidneys of animals.
• Sold in the form of shredded suet and used in Christmas puddings and Suet puddings.

• Fat is present in food either as visible or invisible
• Visible – fat on meat, lard, butter, suet, cooking oil
• Invisible – a constituent part of food, mixed with other ingredients and difficult to detect. Egg yolk, oily fish, nuts, seeds, lean meat (fat is within the muscle)

• When fats spoil, after time, they become rancid.
• Rancidity is caused by two processes: Oxidation & Hydrolytic

Oxidation

• which is a reaction between unsaturated fatty acid molecules and the oxygen in the air. 
• This reaction is accelerated by heat, light and the presence of trace metals.
•   It causes discolouration and the development of ‘off’ flavours and odours.

Hydrolytic

• caused by the action of the enzyme Lipase.
• This causes the fat molecules to be broken down.
• ‘Off’ flavours and odours then occur because of the free fatty acids in the food. 

 Shortening:

• Shortcrust pastry, biscuits and shortbread rely on fat to give them their characteristic crumbly texture.
• The fats coats the flour particles and prevents them from absorbing water. 
• This reduces the formation of gluten development, which would cause the dough to become elastic.
• Fats such as pure vegetable fats or lard are suitable for shortening because of their low water content. 
• There are distinctive colours associated with the type of fat used. 
• Margarine produces a golden colour and lard produces a pale yellow. 
• A compromise is sometimes reached by using a combination of the two.

·      

              Plasticity:

• Fats do not melt at fixed temperatures, but over a range.
• This property is called plasticity.
• It gives all fats unique character.
• The plasticity is due to the mixture of triglycerides, each with its own melting point. Some products are formulated with fats with lower melting points so they can spread from the fridge, e.g. margarine, or melt on the tongue, e.g. chocolate.
• Other fats have a higher melting point and are used for cooking.

·         Aeration: 

• Products such as creamed cakes need air incorporated into the mixture in order to give a well risen texture.
• This is achieved by creaming a fat, such as butter or margarine, with caster sugar.
• Small bubbles of air are incorporated and form a stable foam.

·      

   Flakiness: 

• Flaky and puff pastry use fat to help separate layers of gluten and starch formed in the dough. 
• The fat melts during cooking, leaving minute layers.
• The liquid present produces steam which evaporates and causes the layers to rise.
• The fat prevents the layers sticking together.

·         Retention of moisture: 

• Some fats can help retain a bakery product’s moisture and increase its shelf-life.
•   They may also be used to baste food being cooked by dry heat.

·         Glaze: 

• Placed on hot vegetables, some fats, e.g. butter or margarine, give glossy appearance.
• Fats also add shine to sauces.

Sensory attributes: 

• All fats and oils have unique flavours and odours.
• Some are more suited for particular purposes than others, e.g. olive oil for salad dressing (for flavour) and lard for pastry (due to its blandness).
• They can also contribute to the texture of the food, for example increasing succulence.

Essential fatty acids:

• The body can synthesize most of the fats it needs from the diet.
• However, two essential fatty acids, linolenic and linoleic acid, cannot be synthesized in the body and must be obtained from food.
• These basic fats, found in plant foods, are used to build specialized fats called omega-3 and omega-6 fatty acids.
• Omega-3 and omega-6 fatty acids are important in the normal functioning of all tissues of the body.