Final answer:
Hydrogenation changes the physical state of a lipid from liquid to semi-solid or solid by converting unsaturated fatty acids to saturated ones, thus increasing the melting point. It also creates trans fats, which have a linear shape and provide a consistency desirable for processed foods.
Step-by-step explanation:
When a lipid is hydrogenated, the physical state of the lipid changes from a liquid to a semi-solid or solid form. This transformation is due to the hydrogenation process where hydrogen gas is bubbled through oils containing unsaturated fatty acids. These unsaturated fatty acids have double bonds, often in the cis-conformation, and the process can convert some of these to the trans-conformation, resulting in trans fats. As a consequence of the hydrogenation process, the lipid becomes more solid because the conversion of unsaturated fatty acids to saturated fatty acids increases the melting point of triglycerides.
Partially hydrogenated oils tend to be more desirable for processed food products due to their consistency and increased shelf life. The formation of trans fatty acids during this process gives them a linear shape, similar to saturated fatty acids, making the oils more solid at room temperature. Products such as margarine and shortening are often created using these hydrogenated oils.
It's also important to note that while hydrogenation can improve the desirable physical properties of oils for the food industry, the presence of trans fats has been linked to negative health effects, such as decreasing HDL (good cholesterol) in the body.