Chemistry of Oils & Fats
What are oils and fats?
Like most organic materials, Oils and fats are made up of three elements:-
These elements combine together to form chains known as fatty acids. Three of these chains then join together to form a molecule known as a triglyceride. The tryglyceride molecule is the basis of all oils and fats.
Oils and fats vary in both their appearance and functionality due to differences in the types fatty acid chain which join together to form the triglyceride molecule.
What is the difference between an oil and a fat?
Individual fatty acids can be either saturated or unsaturated and the latter being further sub divided into mono and polyunsaturated. All oils contain a proportion of all three types and it is this combination in any one oil which determines whether it will be a solid fat or liquid oil at ambient temperature. The functionality of liquid oils and solid fats varies considerably and which to choose will depend on the intended application.
Generally speaking, oils containing a greater proportion of unsaturated fatty acids are liquid at room temperature whereas those with higher amounts of saturated fatty acids will be solid.
The chemical structure of fatty acids
Fatty acids are either saturated or unsaturated.
a) Saturated Fats
Certain fatty acids are already ‘naturally saturated’ in that they cannot be made ‘harder’ than they are in nature. As previously noted, the levels of saturates is generally higher in those fats which are solid at ambient temperatures.
Saturated fatty acids are extremely stable i.e. they do not easily become rancid, meaning they have good keeping properties (shelf life). However, Government recommendations advise consumers to limit their intake of saturated fats as they can increase blood cholesterol levels, one of the major factors in heart disease.
Most animal fats such as meat, butter, cheese and cream contain relatively high levels of saturated fat and as such should be eaten in moderation. Many baked goods such as cakes, biscuits and pastries can also be high in saturated fat.
b) Unsaturated Fats
There are three types of unsaturated fatty acids:-
(1) Monounsaturated Fatty Acids (MUFA)
Fatty acids in this category have what is known as one double bond in their chemical make up. They are relatively stable to oxidation and the development of rancidity and are now considered, in nutritional terms, as being the best type of fat to eat.
The most common source of Monounsaturates are Olive Oil and Rapeseed oils.
(2) Polyunsaturated Fatty Acids (PUFA)
Polyunsaturated fatty acids contain two or more double bonds in their chemical make up. They are least stable fatty acids to oxidation and as such are best used in cold applications. The most common source of polyunsaturates is Sunflowerseed oil
(3) Trans Fatty Acids (TFA)
Trans fatty acids typically come from two sources, hydrogenated vegetable oils and animal fats. Recent scientific research suggests trans fats, although consumed in relatively small proportions, should be avoided due to their negative affect blood cholesterol levels.
What does fat provide in the diet?
Fat has many important functions as a nutrient. It provides a concentrated source of energy. 1g of fat provides 37kJ (9kcal), more than double that provided by either protein or carbohydrate which provide 17kJ/g (4kcal) and 16kJ/g (3.75kcal), respectively.
It is a carrier for fat-soluble vitamins A, D, E and K.
Some fats are essential to our well being, these are known as the essential fatty acids (EFA’s) often referred to as the omega fatty acids. Linoleic acid (omega 6) and alpha linolenic acid (omega 3) are the most common essential fatty acids found in vegetable oils. The most prolific source of essential fatty acids are fish oils such as cod liver oil. It is recommended that 1-2% of our energy intake should come from essential fatty acids.