On Food and Cooking

unsaturated fat opens a space unprotected by
hydrogen atoms on one side of the chain. This
exposes the carbon atoms to reactive
molecules that can break the chain and
produce small volatile fragments.
Atmospheric oxygen is just such a reactive
molecule, and is one of the major causes of
flavor deterioration in foods containing fats.
Water and metal atoms from other food
ingredients also help fragmentfats and cause
rancidity. The more unsaturated the fat, the
more prone it is to deterioration. Beef has a
longer shelf life than chicken, pork, or lamb
because its fat is more saturated and so more
stable.
Some small volatile fragments of
unsaturated lipids actually have desirable and
distinctive aromas. The typical aroma of
crushed green leaves and of cucumber both
come from fragments of membrane
phospholipids generated not just by oxygen,
but by special plant enzymes. And the