Recently, consumption of trans fatty acids has been linked to high blood cholesterol levels and increased risk of heart disease. The food industry has responded by decreasing use of "trans fats."

Question

Consider the following questions: (a) How do the structures and transition temperatures of trans, cis, and saturated fatty acids differ, and what are the effects on membrane fluidity? (b) Are trans fatty acids abundant in nature? (c) The major source of trans fats is hydrogenated oils. (The trans fats are produced by a side reaction during the hydrogenation process.) Why has the food industry used synthetically produced hydrogenated oils?
What will be an ideal response?

Answer 1

Answer:
a. The single carbon bonds in saturated fatty acids are saturated with hydrogen bonds and the fatty acid structure can be straight. The terms trans and cis describe the structures of unsaturated carbon double bonds in the fatty acid. In trans carbon double bonds, the hydrogen atoms are on opposite sides of the C=C bond, resulting in a fatty acid chain that is much straighter than one with cis carbon double bonds, where the hydrogen atoms are on the same side of the C=C bond, forming a rigid kink or bend in the fatty acid. The straighter saturated and trans fatty acids can pack closer together and have higher transition temperatures than do cis fatty acids. At a given temperature, membranes with more cis fatty acids are more fluid than are membranes with more trans or saturated fatty acids.
b. Most unsaturated fatty acids found in nature contain cis double bonds.
c. The food industry converted some unsaturated fats to saturated fats by converting carbon-carbon double bonds to single bonds in a process called hydrogenation. This process converts oils (liquid at room temperature) to products that are solid at room temperature. These products (such as Crisco® shortening and margarine) are inexpensive to manufacture, have increased shelf life, and have lower levels of saturated fats than butter or lard. Unfortunately, a side reaction in this process also converts some cis double bonds to the trans double bonds that have been linked to heart disease.