World of Maize

I Introduction

Corn or Maize, common name for the cereal grass widely grown for food and livestock fodder. Corn ranks with wheat and rice as one of the world’s chief grain crops.

Although archaeological evidence indicates that corn has been cultivated for over 7000 years in Mexico, the exact origin of the corn plant remains a mystery. Today corn is one of the most important cereal grains grown worldwide, having been hybridized into numerous varieties for food and non-food purposes. The kernels are used for human and livestock consumption, while the corn cob and its extracts are used for a variety of industrial purposes such as the making of nylon fibers and the production of synthetic rubber.

II Description

The corn plant has an erect, solid stem, rather than the hollow one of most other grasses. It varies widely in height, some dwarf varieties being little more than 60 cm (2 ft) at maturity, whereas other types may reach heights of 6 m (20 ft) or more. The average is 2.4 m (8 ft). The leaves, which grow alternately, are long and narrow. The main stalk terminates in a staminate (male) inflorescence, or tassel. The tassel is made up of many small flowers termed spikelets, and each spikelet bears three small anthers, which produce the pollen grains, or male gametes. The pistillate (female) inflorescence or ear is a unique structure with up to 1,000 seeds borne on a hard core called the cob. The ear is enclosed in modified leaves called husks. The individual silk fibers that protrude from the tip of the ear are the elongated styles, each attached to an individual ovary. Pollen from the tassels is carried by the wind and falls onto the silks, where it germinates and grows down through the silk until it reaches the ovary. Each fertilized ovary grows and develops into a kernel.

III History

Corn is native to the Americas and was the staple grain of the region for many centuries before Europeans reached the New World. The origin of corn remains a mystery. Conclusive evidence exists, from archaeological and paleobotanical discoveries, that cultivated corn has existed in the southwestern United States for at least 3,000 years. Wild corn was once thought to have existed in the Tehuacán Valley of southern Mexico 7,000 years ago. More recent evidence puts the appearance of corn in that region at a much later date, about 4,600 years ago. Early wild corn was not much different in fundamental botanical characteristics from the modern corn plant.

IV Varieties

The many varieties of corn show widely differing characteristics. Some varieties mature in 2 months; others take as long as 11 months. The foliage varies in intensity of color from light to dark green, and it may be modified by brown, red, or purple pigments. Mature ears vary in length from less than 7.5 cm (3 in) to as much as 50 cm (20 in). The number of rows of kernels ranges from 8 to 36 or more. Six general groups of varieties are differentiated by the characteristics of the kernel. Dent corn is the leading type of corn grown on U.S. farms. The sides of the kernel consist of hard, so-called horny starch, and the crown contains soft starch. As the grain matures, this soft starch shrinks, forming the characteristic dent.

In flint corn, the horny starch extends over the top of the kernel, so that there is no denting. Some varieties of flint corn, which are used for the same purposes as dent corn, are favored in cold climates because of their ability to germinate at low temperatures, or in tropical climates because of their resistance to attack by weevils. Popcorn is a light, highly popular snack throughout the United States, a variant of flint corn with small kernels of great hardness. When heated, the moisture in the kernels expands, causing the kernels to pop open.

Flour corn contains a preponderance of soft or less densely packed starch, and it is readily ground into meal. It is grown extensively in the Andean regions of South America that were part of the Inca Empire. Sweet corn is the type commonly grown in the United States for human consumption as a vegetable. The sugar produced by the sweet-corn plant is not converted to starch during growth, as it is in other types. The seeds are characteristically wrinkled when the plant is allowed to mature. Pod corn is seldom used as food but is often grown as a decorative plant; each kernel is enclosed in its own set of diminutive husks. Another decorative corn, commonly called Indian corn, consists of multicolored varieties of flour and flint types.

VII Production and Consumption

World output of corn at the beginning of the 21st century was about 603 million metric tons annually; in volume of production, corn ranked first, ahead of rice and wheat. A net gain of about 51 percent in production was realized during the last two decades; intensive cultivation with heavy use of fertilizer and herbicides was responsible for the increase. The United States is the leading corn-growing country, with about 40 percent of the world’s production. The other leading corn-growing nations are China, Brazil, Mexico, France, Argentina and India.

Approximately three-fifths of the corn sold by farmers in the United States is used as livestock feed. About half of that amount is fed directly to hogs, cattle, and poultry, and the rest is used in mixed feeds. Another one-fifth of U.S. corn is exported; the remaining one-fifth is sold as food and taken by commercial users for the production of alcohol and distilled spirits, syrups, sugar, cornstarch, and dry-process foods.

Corncobs are an important source of furfural, a liquid used in manufacturing nylon fibers and phenol-formaldehyde plastics, refining wood resin, making lubricating oils from petroleum, and purifying butadiene in the production of synthetic rubber. Ground corncobs are used as a soft-grit abrasive. Large, whole cobs from a special type of corn, “cob pipe” corn, are used for pipes for smoking tobacco. Corn oil, extracted from the germ of the corn kernel, is used as a cooking and salad oil and, in solidified form, as margarine; it is also used in the manufacture of paints, soaps, and linoleum. The search for alternate sources of energy has brought attention to corn as a fuel source. High in sugar content, corn is processed to produce alcohol for use with gasoline as gasohol, and the dry stalk is a potentially important fuel biomass.

Products

Maize, the American Indian word for corn, means literally "that which sustains life". It is, after wheat and rice, the most important cereal grain in the world, providing nutrients for humans and animals and serving as a basic raw material for the production of starch, oil and protein, alcoholic beverages, food sweeteners and, more recently, fuel.

Nutritional value of Maize

The importance of cereal grains to the nutrition of millions of people around the world is widely recognized. Because they make up such a large part of diets in developing countries, cereal grains cannot be considered only as a source of energy, as they provide significant amounts of protein as well. It is also recognized that cereal grains have a low protein concentration and that protein quality is limited by deficiencies in some essential amino acids, mainly lysine Much less appreciated, however, is the fact that some cereal grains contain an excess of certain essential amino acids that influence the efficiency of protein utilization. The classic example is maize. Other cereal grains have the same constraints but less obviously.

Starch

The major chemical component of the maize kernel is starch, which provides up to 72 to 73 percent of the kernel weight. Other carbohydrates are simple sugars present as glucose, sucrose and fructose in amounts that vary from 1 to 3 percent of the kernel. The starch in maize is made up of two glucose polymers: amylose, an essentially linear molecule, and amylopectin, a branched form. The composition of maize starch is genetically controlled. In common maize, with either the dent or flint type of endosperm, amylose makes up 25 to 30 percent of the starch and amylopectin makes up 70 to 75 percent. Waxy maize contains a starch that is 100 percent amylopectin. An endosperm mutant called amylose-extender (ae) induces an increase in the amylose proportion of the starch to 50 percent and higher.

Dietary fibre

After carbohydrates, proteins and fats, dietary fibre is the chemical component found in the greatest amounts. The complex carbohydrate content of the maize kernel comes from the pericarp and the tip cap, although it is also provided by the endosperm cell walls and to a smaller extent the germ cell walls.