|
Corn Nutritional Profile
Energy value (calories per serving): Moderate
Protein: Moderate
Fat: Low
Saturated fat: Low
Cholesterol: None
Carbohydrates: High
Fiber: High
Sodium: Low
Major vitamin contribution: Vitamin A (in yellow corn), B vitamins,
vitamin C
Major mineral contribution: Potassium
About the Nutrients in Corn
Like other grains, corn is a high-carbohydrate, high-fiber food.
Eighty-one percent of the solid material in the corn kernel consists of
sugars, starch, and dietary fiber, including insoluble cellulose and
non-carbohydrate lignin in the seed covering and soluble pectins and gums
in the kernel.* Corn has small amounts of vitamin A, the B vitamin folate,
and vitamin C.
Corn is a moderately good source of plant proteins, but zein (its major
protein) is deficient in the essential amino acids lysine, cystine, and
tryptophan. Corn is low in fat and its oils are composed primarily of
unsaturated fatty acids.
Yellow corn, which gets its color from the xanthophyll pigments lutein and
zeaxanthine plus the vitamin A-active pigments carotene and cryptoxanthin,
contains a little vitamin A; white corn has very little.
One fresh ear of yellow corn, 5 inches long, has 3 g dietary fiber, 1 g
fat (0.1 g saturated fat), 160 IU vitamin A (3.2 percent of the RDA for a
man, 4 percent of the RDA for a woman), 23 mcg folate (11.5 percent of the
RDA for a man, 12.7 percent of the RDA for a woman), and 4 mg vitamin C
(6.6 percent of the RDA).
* The most plentiful sugar in sweet corn is
glucose; hydrolysis (chemical splitting) of corn starch is the principal
industrial source of glucose. Since glucose is less sweet than sucrose,
sucrose and fructose are added to commercial corn syrup to make it
sweeter.
The Most Nutritious Way to Serve Corn
With beans (which are rich in lysine) or milk (which is rich in lysine and
tryptophan), to complement the proteins in corn.
With meat or a food rich in vitamin C, to make the iron in corn more
useful.
Diets That May Restrict or Exclude Corn
Low-fiber diet
Buying Corn
Look for: Cobs that feel cool or are stored in a refrigerated bin. Keeping
corn cool helps retain its vitamin C and slows the natural conversion of
the corn's sugars to starch.
Choose fresh corn with medium-sized kernels that yield slightly when you
press them with your fingertip. Very small kernels are immature; very
large ones are older and will taste starchy rather than sweet. Both yellow
and white kernels may be equally tasty, but the husk of the corn should
always be moist and green. A dry yellowish husk means that the corn is old
enough for the chlorophyll pigments in the husk to have faded, letting the
carotenes underneath show through.
Storing Corn
Refrigerate fresh corn. At room temperature, fresh-picked sweet corn will
convert nearly half its sugar to starch within 24 hours and lose half its
vitamin C in four days. In the refrigerator, it may keep all its vitamin C
for up to a week and may retain its sweet taste for as long as ten days.
Preparing Corn
Strip off the husks and silk, and brush with a vegetable brush to get rid
of clinging silky threads. Rinse the corn briefly under running water, and
plunge into boiling water for four to six minutes, depending on the size
of the corn.
What Happens When You Cook Corn
Heat denatures (breaks apart) the long-chain protein molecules in the
liquid inside the corn kernel, allowing them to form a network of protein
molecules that will squeeze out moisture and turn rubbery if you cook the
corn too long. Heat also allows the starch granules inside the kernel to
absorb water so that they swell and eventually rupture, releasing the
nutrients inside. When you cook corn, the trick is to cook it just long
enough to rupture its starch granules while keeping its protein molecules
from turning tough and chewy.
Cooking fresh corn for several minutes in boiling water may destroy at
least half of its vitamin C. At Cornell University, food scientists found
that cooking fresh corn in the microwave oven (two ears/without water if
very fresh/4 minutes/600–700 watts) preserves most of the vitamin C.
How Other Kinds of Processing Affect Corn
Canning and freezing. Canned corn and frozen corn both have less vitamin C
than fresh-cooked corn. The vitamin is lost when the corn is heated during
canning or blanched before freezing to destroy the natural enzymes that
would otherwise continue to ripen it. Blanching in a microwave oven rather
than in boiling water can preserve the vitamin C in frozen corn (see
above).
Milling. Milling removes the hull and germ from the corn kernel, leaving
what is called hominy. Hominy, which is sometimes soaked in wood ash (lye)
to increase its calcium content, can be dried and used as a cereal (grits)
or ground into corn flour. Coarsely ground corn flour is called cornmeal.
Processed corn cereals. All processed, ready-to-eat corn cereals are much
higher in sodium and sugar than fresh corn.
Added calcium carbonate. Pellagra is a niacin-deficiency disease that
occurs most commonly among people for whom corn is the staple food in a
diet lacking protein foods with the essential amino acid tryptophan, which
can be converted to niacin in the human body. Pellagra is not an
inevitable result of a diet high in corn, however, since the niacin in
corn can be made more useful by soaking the corn in a solution of calcium
carbonate (lime) and water. In Mexico, for example, the corn used to make
tortillas is boiled in a dilute solution of calcium carbonate (from shells
or limestone) and water, then washed, drained, and ground. The alkaline
bath appears to release the bound niacin in corn so that it can be
absorbed by the body.
Medical Uses and/or Benefits of Corn
As a wheat substitute in baking. People who are allergic to wheat or
cannot tolerate the gluten in wheat flour or wheat cereals can often use
corn flour or hominy instead.
Bath powder. Corn starch, a fine powder refined from the endosperm (inner
part) of the corn kernel, can be used as an inexpensive, un-perfumed body
or face powder. Because it absorbs oils, it is also used as an ingredient
in dry shampoos.
Adverse Effects Associated with Corn
Allergic reaction. According to the Merck Manual, corn is one of the 12
foods most likely to trigger the classic food allergy symptoms: hives,
swelling of the lips and eyes, and upset stomach. The others are berries
(blackberries, blueberries, raspberries, strawberries), chocolate, eggs,
fish, legumes (green peas, lima beans, peanuts, soybeans), milk, nuts,
peaches, pork, shellfish, and wheat.
|
