Unsatrurated oils can be hydrogenated by adding hydrogen in the presence of a catalyst, at a room temperature of 60C. The process opens up the double bonds in the oil. This causes them to harden, as the new hydrogenated substance has a higher melting point. As completly hydrogenating makes the oils denser, it is common that the oils are only partially hydrogenated to make it a better consistency for spreading. It is primarly used as it increases the shelf-life of a product such as biscuts. However the only problem with patially hydrogenated oils is; they have lots of trans fats which research suggest is very bad for you as they incrase blood cholesterol, and increases the risk of heart disease.
Emulsions are formed from to liquids, one of which is suspended within the other. In order to fully emulsify the mixture and emulsifier is added e.g. egg to sonflower oil and water = mayonnaise. The emusifier contains a hydrophobic and a hydrophilic, one end is attracted to oil and hates water (hydrophobic) while the other likes water and hates oil (hydrophilic). these prvent the emulsion from seperating ever. However some people are allergic ro the emulsifier.