Polyunsaturated edible oils are unstable because of their high content of the polyunsaturated fatty acids (PUFAs), linoleic acid (LA) and alpha-linolenic acid (ALA). These oils are therefore very susceptible to attack by air and moisture to form unhealthy oxidised compounds. As such, PUFA-rich edible oils are usually stabilised by partial hydrogenation to reduce their PUFA content. Very often, a chemical antioxidant is also added to the oil to improve shelf-life.
Polyunsaturated edible oils are liquids and would need to be first “hardened” by hydrogenation in order that they may attain the semi-solid nature for manufacture of food products such as margarines, shortenings, vegetable ghee, confectionery, and bakery products.
During the hydrogenation process carried out at high temperatures, the fatty acids in these oils are transformed into the trans fatty acids (TFAs) which are harmful to health. Such hydrogenated fats, containing TFAs, are also referred to as “trans fats”.