See also Flour, Vegetable oils, Wheat cereals.
Energy value (calories per serving): Moderate
Saturated fat: Low
Cholesterol: None Carbohydrates: High Fiber: High
Major vitamin contribution: Vitamin A (in yellow corn), B vitamins, vitamin C
Major mineral contribution: Potassium
About the Nutrients in This Food
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 noncarbohydrate 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 zeaxanthin 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, 5.5– 6.5 inches long, has three grams dietar y fiber, one gram fat (0.1 g saturated fat, 0.3 g monounsaturated fat, 0.4 mg polyunsaturated fat), 137 IU vitamin A (6 percent of the R DA for a woman, 5 percent of the R DA for a man), 34 mcg folate (9 percent of the R DA), and 5 mg vitamin C (7 percent of the R DA for a woman, 6 percent of the R DA for a man).
* The most plent iful sugar in sweet corn is glucose; hydrolysis (chemical splitt ing) of corn starch is t he principal indust rial source of glucose. Since glucose is less sweet t han sucrose, sucrose and fructose are added to commercial corn syrup to make it sweeter.
The Most Nutritious Way to Serve This Food
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 This Food
Buying This Food
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 This Food
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 refrigera- tor, 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 This Food
Strip off the husks and silk, and brush with a vegetable brush to get rid of clinging silky threads. R inse 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 This Food
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 This Food
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. Blanch- ing 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 con- tent, 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 com- monly 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
As a wheat substitute in baking. People who are allergic to wheat or cannot tolerate the glu- ten 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, unperfumed body or face powder. Because it absorbs oils, it is also used as an ingredient in dry shampoos.
Adverse Effects Associated with This Food
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), choco- late, eggs, fish, legumes (green peas, lima beans, peanuts, soybeans), milk, nuts, peaches, pork, shellfish, and wheat (see wheat cer ea ls).