Do not discard lettuce simply because the core begins to brown or small brown specks
appear on the spines of the leaves. This is a natural oxidation reaction that changes the color
but doesn’t affect the nutritional value of the lettuce. Trim the end of the core (or remove the
core from iceberg lettuce) to slow the reaction. Throw out any lettuce that feels slimy or has
bright red, dark brown, or black spots. The slime is the residue of bacterial decomposition;
the dark spots may be mold or rot.
Do not store unwrapped lettuce near apples, pears, melons, or bananas. These fruits
release ethylene gas, a natural ripening agent that will cause the lettuce to develop brown
spots.
Preparing This Food
Wash all lettuce, including lettuce sold in “pre-washed” packages of salad mix, to flush
out debris.
Never slice, cut, or tear lettuce until you are ready to use it. When lettuce cells are
torn, they release ascorbic acid oxidase, an enzyme that destroys vitamin C.
What Happens When You Cook This Food
Chlorophyll, the pigment that makes green vegetables green, is sensitive to acids. When you
heat lettuce, the chlorophyll in its leaves will react chemically with acids in the vegetable or
in the cooking water, forming pheophytin, which is brown. Together, the pheophytin and
the yellow carotenes in dark green leaves will give the cooked lettuce a bronze hue. (Lighter
leaves, with very little carotene, will be olive-drab.)
To keep cooked lettuce green, you have to keep the chlorophyll from reacting with
acids. One way to do this is to cook the lettuce in a large quantity of water (which will dilute
the acids), but this will accelerate the loss of vitamin C. A second alternative is to cook the
lettuce with the lid off the pot so that the volatile acids will float off into the air. The best
way may be to steam the lettuce quickly in very little water, so that it holds onto its vitamin
C and cooks before the chlorophyll has time to react with the acids.
Heat also makes the water inside the lettuce cells expand. Eventually the cells rupture
and the water leaks out, leaving the lettuce limp. The spines will remain stiffer because they
contain more cellulose, which does not dissolve in water. Cooked lettuce has less vitamin C
than fresh lettuce because heat destroys the vitamin.
How Other Kinds of Processing Affect This Food
Medical Uses and/or Benefits
Lower risk of some birth defects. Up to two of every 1,000 babies born in the United States
each year may have cleft palate or a neural tube (spinal cord) defect due to their mothers’ not
Lettuce