Question

Every biochemistry student knows that most naturally occurring unsaturated fatty acids are "cis" fatty acids. Why then do so many fat-containing foods come with the notation "contains no trans fats"?

A) Vegetable oils contain polyunsaturated fatty acids prone to oxidation, which then convert them to trans fats.

B) Olive oils, normally healthy oils, are converted to trans fat when cooked at high temperatures. Thus, olive oils are used only at low temperatures.

C) Vegetable oils are often hydrogenated to form trans unsaturated fatty acids to preserve shelf life.

D) Oils that contain an odd number of carbon atoms are particularly susceptible to reduction to trans fats. Thus, no odd number carbon fatty acids are used in these foods.

Answer 1

In naturally occurring monounsaturated fatty acids the double bond usually has the cis configuration.

In unsaturated fatty acids the double bonds are usually cis in geometry. Hence the hydrocarbon chains of the fatty acids could not be closely packed. The gap produced in the cell membrane due to presence of the double bond provides the passage for the biologically important chemicals. Moreover such lose packing lowers the melting and boiling point of cis fatty acids. In case of trans fatty acids the packing pattern is similar to those of saturated fatty acids and the melting point and boiling point are usually higher.

Vegetable oils are often hydrogenated to form trans unsaturated fatty acids to preserve shelf life. But as the hydrogenation protocol is reversible a partial hydrogenation is achived. Partial hydrogenation processes involving triacylglycerols effect the conversion of some cis double bonds to single bonds and conversion of the rest cis double bonds to trans double bonds.

So, the correct option is (c).