IC EX O S M Specialty Corns Cooperative Extension Service T A W T E College of Agriculture and E N U Home Economics N Y I I T Guide H-232 V E R S George W. Dickerson, Extension Horticulture Specialist This publication is scheduled to be updated and reissued 2/08. History (tissue surrounding the embryo that provides food for the seed’s growth). Five hundred years ago, Columbus became one of The most common types of corn include flint, the first Europeans to set eyes on maize or corn (Zea flour, dent, pop, sweet, and waxy. The physical ap- mays), the foundation of most great New World civili- pearance of each kernel type is determined by its pat- zations, including those of the Incas, Mayans, and Az- tern of endosperm composition as well as quantity tecs. In 1540, Coronado found pueblo Indians grow- and quality of endosperm (fig. 1). ing corn under irrigation in the American Southwest. A seventh type of corn called pod or tunicate may The Jamestown Colony learned how to grow corn also be characterized by flint, dent, flour, sweet, pop, from the Indians in 1608, and corn helped keep the or waxy endosperms. In pod corns, however, each in- Pilgrims alive during the winter of 1620. dividual kernel is enclosed in a glume, or husk. These The inability of corn to survive in the wild on its types have little commercial value except as an orna- own makes its ancestry a puzzle. Probably the oldest ment. known remains of corn are cobs dating back 7000 Kernels of flint corn have mostly hard, glassy en- years found in Tehucan, Mexico. Most corn historians dosperms with smooth, hard seed coats (pericarps). feel that a wild grass called Teosinte is probably one Flour corn endosperms are made of soft starch with of its primary ancestors. An eight-row race called thin pericarps. Dent corns with flinty sides and soft Harinoso de Ocho was known to have been grown in cores of starch that cause the end of the kernels to col- the Southwest about 700 AD. lapse or dent during drying fall between the flint and flour types. Popcorns are basically small-kerneled Corn Classification flint-type corns. The wrinkled, glassy appearance of sweet corn kernels is the result of a sugary gene that Corn is one of the most diverse grain crops found retards the normal conversion of sugar to starch dur- in nature. Selection pressure by both humans and na- ing endosperm development. Waxy corn carries a ture has resulted in various types of corn generally gene that produces 100% amylopectin (a complex classified by characteristics of their kernel endosperm form of starch). ENDOSPERM Hard Soft Sugary Germ Pop Flint Dent Flour Sweet Fig. 1. Endosperm distribution in five types of corn kernels. To find more resources for your business, home, or family, visit the College of Agriculture and Home Economics on the World Wide Web at aces.nmsu.edu Dent Corn high-fiber, no-calorie flour from sweet corn pericarps. Immature standard sweet corn is considered desirable Today’s dent corns originally came from crosses when kernels are succulent because of a mutant reces- between late-flowering Southern dent corns sive sugary-1 gene (su-1) that retards the conversion (Gourdseed) and early-flowering Northern flints. of sugar into starch during endosperm development. Modern-day hybrid dent varieties grown in New In comparison, sucrose produced in leaves from pho- Mexico can produce over 12,000 lb of grain per acre. tosynthesis in dent corn is passed on to developing Although most dent corns produced in the United kernels, where it is rapidly converted to dextrin (a States have yellow endosperms, white dents are very nonsweet, water-soluble polysaccharide), and then to popular in human food products because of the whiter starch. The sugary-1 gene slows down this process. starch. White dent corns often receive a premium Field corn contains approximately 4% sucrose in price from the dry-milling industry since yields are the immature milky stage. Standard sweet corn at the somewhat less than those of the yellow dent corn hybrids. same stage contains approximately 10% sucrose. Fol- While the foliage and stalks of dent corn can be lowing harvest, or if left on the stalk too long, sucrose used to make a number of products including silage in standard sweet corn is rapidly converted to starch. and corn syrups, the kernels make dent corn an eco- Kernels can lose as much as 50% of their sucrose at nomic agricultural giant. On the average, the United room temperature 24 hours after harvest. States produce over 7 billion bushels of dent corn per In the past, sweeter varieties have been developed year, 85% of which goes into animal feed or exports. by selections within the homozygous su-1 genotype. Processed corn products are diverse, including One such selection, ‘Silver Queen’, became the stan- cooking oil and various corn grits, meals, flours, and dard to which other varieties were compared. A starches. Corn starches can be processed further into a sweetness breakthrough was accomplished with the variety of food and nonfood products including fat discovery of the shrunken (sh-2) gene. Supersweet substitutes, sweeteners, alcohol, paper, adhesives, varieties with this gene exhibit sucrose levels two to paints, soaps, cosmetics, dynamite, tires, and oil-drill- three times greater than standard sweet corn at har- ing materials. vest, and two days after harvest sucrose levels will Corn is also used as a nutrient medium in making still be relatively high. antibiotics like tetracycline, penicillin, neomycin, ba- Although sh-2 varieties contain more sucrose at citracin, and streptomycin. Riboflavin (Vitamin B2) and after harvest than standard sweet corn, they ex- and cobalmide (Vitamin B12) are two major vitamins hibit some notable disadvantages. Early releases produced from the fermentation of corn steep liquor tended to have tough pericarps and lacked the high and dextrose. Other important corn fermentation prod- levels of water-soluble polysaccharides that give stan- ucts include citric acid, glutamic acid, lactic acid, and dard sweet corn its creamy texture. They also must be lysine. isolated from other varieties of sweet corn, because Although most of the products listed above are cross pollination with standard sweet corn will make made from dent corn, other types of corn are becom- kernels tough and starchy in both types. ing more and more important as growers seek to capi- Germination in supersweet varieties is also poor. For talize on niche markets or competitive advantages for good stand establishment, planting depth should be shal- specialty corns in localized markets. lower and soils warmer than for standard sweet corn. ‘Kandy Korn’ is an example of a variety exhibiting Sweet Corn another type (Everlasting Heritage) of gene that results in sweeter sweet corn. In combination with the su-1 Sweet corn probably originated from a mutation of gene, the “sugar enhanced” (se) gene produces a vari- a Peruvian corn called Chuspillo or Chullpi. Ameri- ety with increased sweetness and creamy texture, re- can Indians grew selections of this mutant race; quiring no isolation. Varieties with the se gene have ‘Papoon’ grown by the Iroquois in 1779 is the most sugar levels that normally peak somewhere between well known. ‘Dantings Early’ was one of the first- su-1 and sh-2 varieties. named sweet corn varieties, while ‘Golden Bantam,’ Marketing sweet corn effectively depends on promo- released in 1902, became one of the most important tion and educating the consumer to differences between open-pollinated varieties. In later hybrid breeding tri- varieties. For shipping purposes, sh-2 varieties are excel- als, ‘Iochief’ was developed for the processing indus- lent because sugar conversion to starch is much slower. try. High-quality se varieties are popular for roadside Unlike dent corn, sweet corn is grown primarily for stands. Free samples along with recipes are an excellent fresh consumption, not feed or flour, although USDA way to promote these varieties. researchers have developed a technique to produce a Guide H-232 • Page 2 Popcorn lysine and tryptophan, two of the eight essential amino acids that nonruminants cannot synthesize Popcorn is one of the oldest forms of corn. Pod and must obtain from their diet. forms of popcorn found in Bat Cave, New Mexico, In 1963, scientists at Purdue University found that have been radioactive carbon dated at 3600 BC. corn strains with opaque-2 (o-2) genes contained Popcorns can be generally classified into two pri- lower amounts of zein and higher amounts of lysine mary types: pearl or rice. Pearl types have smooth, and tryptophan in their endosperms than standard dent rounded pearl-like crowns, while rice types are corn. The opaque-2 gene changes the starch structure pointed. Popcorns also vary in color. Popcorn has a in the endosperm, elevating the glutelin (the protein hard, flinty endosperm that surrounds a small amount high in lysine and tryptophan) level and lowering the of soft moist starch in the center. Heating the kernel prolamine level. Opaque-2 kernels, however, tend to turns this moisture into steam which expands, splits have soft textures, dull appearances, and very little the pericarp (seed coat), and causes the endosperm to hard endosperm, making them difficult to harvest and explode, turning the kernel inside out. The moisture more subject to attack by pests. Opaque-2 varieties content should be 13.5–14% for best results. also tend to give lower yields and must be isolated Popcorn quality depends on a number of factors. from other corns to retain protein quality. Though Generally, the more a popcorn variety expands after high-lysine corn continues to show great potential as a popping, the better the quality, as a greater volume more balanced protein for nonruminant animals and produces a better texture.