Biology:Sweet corn

Sweet corn
Husked sweet corn
Species	Zea mays convar. saccharata var. rugosa
Origin	United States

Loose kernels of sweet corn

Sweet corn (Zea mays convar. saccharata var. rugosa; also called sweetcorn, sugar corn and pole corn) is a cereal with a high sugar content. Sweet corn is the result of a naturally occurring recessive mutation in the genes which control conversion of sugar to starch inside the ENO of the corn kernel. Unlike field corn varieties, which are harvested when the kernels are dry and mature (dent stage), sweet corn is picked when immature (milk stage) and prepared and eaten as a vegetable, rather than a grain. Since the process of maturation involves converting sugar to starch, sweet corn stores poorly and must be eaten fresh, canned, or frozen, before the kernels become tough and starchy.

It is one of the six major types of corn, the others being dent corn, flint corn, pod corn, popcorn, and flour corn.

Sweet corn, yellow, raw
(seeds only)

Nutritional value per 100 g (3.5 oz)
Energy	360 kJ (86 kcal)
Carbohydrates	19.02 g
Sugars	3.22 g
Dietary fiber	2.7 g
Fat	1.18 g
Protein	3.2 g
Tryptophan	0.023 g
Threonine	0.129 g
Isoleucine	0.129 g
Leucine	0.348 g
Lysine	0.137 g
Methionine	0.067 g
Cystine	0.026 g
Phenylalanine	0.150 g
Tyrosine	0.123 g
Valine	0.185 g
Arginine	0.131 g
Histidine	0.089 g
Alanine	0.295 g
Aspartic acid	0.244 g
Glutamic acid	0.636 g
Glycine	0.127 g
Proline	0.292 g
Serine	0.153 g
Vitamins	Quantity %DV†
Vitamin A equiv.	1% 9 μg
Thiamine (B1)	17% 0.200 mg
Niacin (B3)	11% 1.700 mg
Folate (B9)	12% 46 μg
Vitamin C	8% 6.8 mg
Minerals	Quantity %DV†
Iron	4% 0.52 mg
Magnesium	10% 37 mg
Potassium	6% 270 mg
Other constituents	Quantity
Water	75.96 g
One ear of medium size (6-¾ to 7-½ inches long) maize has 90 grams of seeds
Units μg = micrograms • mg = milligrams IU = International units
†Percentages are roughly approximated using US recommendations for adults. Source: USDA Nutrient Database

History

Sweet corn occurs as a spontaneous mutation in field corn and was grown by several Native American tribes. The Iroquois gave the first recorded sweet corn (called 'Papoon') to European settlers in 1779. It soon became a popular food in southern and central regions of the United States.

Young sweet corn

The same rows of corn 41 days later at maturity.

Open pollinated cultivars of white sweet corn started to become widely available in the United States in the 19th century. Two of the most enduring cultivars, still available today, are 'Country Gentleman' (a Shoepeg corn with small kernels in irregular rows) and 'Stowell's Evergreen'.

Sweet corn production in the 20th century was influenced by the following key developments:

• hybridization allowed for more uniform maturity, improved quality and disease resistance
  • In 1933 'Golden Cross Bantam' was released. It is significant for being the first successful single-cross hybrid and the first specifically developed for disease resistance (Stewart's wilt in this case).
• identification of the separate gene mutations responsible for sweetness in corn and the ability to breed cultivars based on these characteristics:
  • su (normal sugary)
  • se (sugary enhanced, originally called Everlasting Heritage)
  • sh2 (shrunken-2)

There are currently hundreds of cultivars, with more constantly being developed.

Anatomy

The fruit of the sweet corn plant is the corn kernel, a type of fruit called a caryopsis. The ear is a collection of kernels on the cob. Because corn is a monocot, there is always an even number of rows of kernels. The ear is covered by tightly wrapped leaves called the husk. Silk is the name for the pistillate flowers, which emerge from the husk. The husk and silk are removed by hand, before boiling but not necessarily before roasting, in a process called husking or shucking.

Consumption

In most of Latin America, sweet corn is traditionally eaten with beans; each plant is deficient in an essential amino acid that happens to be abundant in the other, so together sweet corn and beans form a protein-complete meal. In Brazil , sweet corn cut off from the cobs is generally eaten with peas (where this combination, given the practicality of steamed canned grains in an urban diet, is a frequent addition to diverse meals such as salads, stews, seasoned white rice, risottos, soups, pasta, and whole sausage hot dogs).

Similarly, sweet corn in Indonesia is traditionally ground or soaked with milk, which makes available the B vitamin niacin in the corn, the absence of which would otherwise lead to pellagra; in Brazil, a combination of ground sweet corn and milk is also the basis of various well-known dishes, such as pamonha and the pudding-like dessert curau, while sweet corn eaten directly off the cobs tends to be served with butter.

The kernels are boiled or steamed. In Europe, China, Korea, Japan and India, they are often used as a pizza topping, or in salads. Corn on the cob is a sweet corn cob that has been boiled, steamed, or grilled whole; the kernels are then eaten directly off the cob or cut off. Creamed corn is sweet corn served in a milk or cream sauce. Sweet corn can also be eaten as baby corn.

In the United States, sweet corn is eaten as a steamed vegetable, or on the cob, usually served with butter and salt. It can be found in Tex-Mex cooking in chili, tacos, and salads. When corn is mixed with lima beans it is called succotash. Sweet corn is one of the most popular vegetables in the United States. Fresh, canned and frozen sweet corn rank among the top ten vegetables in value and per capital consumption. Frozen cut corn is exceeded only by frozen potato products while frozen corn on the cob is 4th following peas.

If left to dry on the plant, kernels may be taken off the cob and cooked in oil where, unlike popcorn, they expand to about double the original kernel size and are often called corn nuts. A soup may also be made from the plant, called sweet corn soup.

Health benefits

Overripe sweet corn

Cooking sweet corn increases levels of ferulic acid, which has anti-cancer properties.

Cultivars

Open pollinated (non-hybrid) corn has largely been replaced in the commercial market by sweeter, earlier hybrids, which also have the advantage of maintaining their sweet flavor longer. su cultivars are best when cooked within 30 minutes of harvest. Despite their short storage life, many open pollinated cultivars such as 'Golden Bantam' remain popular for home gardeners and specialty markets, or are marketed as heirloom seeds. Although less sweet, they are often described as more tender and flavorful than hybrids.

Genetics

Early cultivars, including those used by Native Americans, were the result of the mutant su ("sugary") allele. They contain about 5–10% sugar by weight.

Supersweet corn are cultivars of sweet corn which produce higher than normal levels of sugar developed by University of Illinois at Urbana–Champaign professor John Laughnan. He was investigating two specific genes in sweet corn, one of which, the sh2 gene, caused the corn to shrivel when dry. After further investigation Laughnan discovered that the endosperm of sh2 sweet corn kernels store less starch and from 4 to 10 times more sugar than normal su sweet corn. He published his findings in 1953, disclosing the advantages of growing supersweet sweet corn, but many corn breeders lacked enthusiasm for the new supersweet corn. Illinois Foundation Seeds Inc. was the first seed company to release a supersweet corn and it was called 'Illini Xtra Sweet', but widespread use of supersweet hybrids did not occur until the early 1980s. The popularity of supersweet corn rose due to its long shelf life and large sugar content when compared to conventional sweet corn. This has allowed the long-distance shipping of sweet corn and has enabled manufacturers to can sweet corn without adding extra sugar or salt.

Cut White Sweet Corn

The third gene mutation to be discovered is the se or "sugary enhanced" allele, responsible for so-called "Everlasting Heritage" cultivars, such as 'Kandy Korn'. Cultivars with the se alleles have a longer storage life and contain 12–20% sugar.

All of the alleles responsible for sweet corn are recessive, so it must be isolated from other corn, such as field corn and popcorn, that release pollen at the same time; the endosperm develops from genes from both parents, and heterozygous kernels will be tough and starchy.

Sweet Corn.

The se and su alleles do not need to be isolated from each other. However supersweet cultivars containing the sh2 allele must be grown in isolation from other cultivars to avoid cross-pollination and resulting starchiness, either in space (various sources quote minimum quarantine distances from 100 to 400 feet or 30 to 120 m) or in time (i.e., the supersweet corn does not pollinate at the same time as other corn in nearby fields).

Modern breeding methods have also introduced cultivars incorporating multiple gene types:

• sy (for synergistic) adds the sh2 gene to some kernels (usually 25%) on the same cob as a se base (either homozygous or heterozygous)
• augmented sh2 adds the se and su gene to a sh2 parent

Often seed producers of the sy and augmented sh2 types will use brand names or trademarks to distinguish these cultivars instead of mentioning the genetics behind them. Generally these brands or trademarks will offer a choice of white, bi-color and yellow cultivars which otherwise have very similar characteristics.

Bt corn

Bt corn is genetically modified to resist certain insects. Commercial growers have access to sweet corn seed bred with this artificial trait. Bt corn and other transgenic varieties are not available to the home grower due to protocols that must be followed in their production.

See also

• List of sweetcorn varieties
• Cornbread
• Cornmeal
• Creamed corn
• Frozen vegetables
• Corn syrup