Sunday, July 12, 2009


A highly important cereal crop of the genus Triticum of the grass family, Gramineae, wheat was probably first cultivated in the Euphrates Valley nerly 9000 years ago. Since that time wheat was been a significant food source for people and animals. The most important species include common wheat, T. vulgare, used in bread, durum wheat, used in cakes and pastries and Polish wheat, T. polonicum.

Most of the approximately 30 species of wheat have hollow stems. The leaves are long and narrow. The head is characterized by flowers numbering 20 to 100 and occurring in spikelets. Fertilization of the flowers produces grain. A deep crease extends the length of a kernel, and many short hairs occur on the kernel’s small end. The entire kernel is surrounded by the pericarp, or outer bran, which is difficult to remove and represents 15% of the kernel. The rest of the kernel is composed of endorsperm (83 %) and germ (1.5 %). The object of flour milling is to separate these constituents.

The wheat plant adapts to a wide range of environmental conditions, from those in the Arctic Circle to those in the tropics. It is best cultivated in temperate areas with 250 to 750 mm (10 to 30 in) of yearly rainfall. Wheat cultivation spread throughout the world with the advent of trade. It was unknown in the Western Hemisphere until the Spanish brought it to the Americas in 1519. For thousand of years the sickle remained was done by beating to separate the kernels from the hulls. When the reaper was invented in about 1830, mechanical operations were used for cutting and threshing. Today self propelled combined are common.

Depending on variety, planting time, and environment, commercial wheat are classified as hard or soft, spring or winter, white or red, or durum wheat. After the wheat seed is planted, it starts to absorb moisture and swell, and soon the pericarp, located at the germ end, ruptures. The primary bud emerges, then lateral rootlets. The plant pushes up through the soil, soon forming foliage. Leaves grow from the base area near the stem, therefore, grazing or cutting does not prevent renewed growth. Winter wheat can thus be pastured without harming the plant.

As the plant grows, short stems form branches, called tillers, close to the ground, these become straw. The head begins to develop and emerges from the leaf sheath, flowering takes place, and fertilization occurs. Some flowers are sterile.

Environment hazards to the wheat plant are drought, freezing temperature, and wind erosion. Wheat is subject to numerous diseases (mosaics, smuts, and rusts, for example) and insects (such as grasshoppers and locusts, Hessian files, green bugs, army worms, and weevils). Plant breeding research has eliminated or drastically reduced damage caused by many of the diseases and insects afflict wheat.

Wheat breeding programs in many world wide research centers have sought higher yield, improved baking quality, and enhanced nutrition. The first big stride in yield potential occurred with the introduction of semidwarf varieties responsive to fertilizer applications and insensitive to length of day. Semidwarf wheat, because of its shorter straw, leaves less material on the field during harvesting.

Improving the chemical and physical properties of the wheat kernel depend on the plant breeder’s skill and knowledge in manipulating in genes controlling these characteristics. The hard wheat breeding programs have two objectives, to increase protein content and to enhance protein quality. Until recently, improved, newer varieties are high yielding and maintain high protein content as well. The nutritive value of wheat protein does not differ much among varieties as measured by amino acid; consequently, efforts have been directed to producing varieties with higher lysine content.

Wheat and other cereal grains do not contain appreciable amount of vitamin A, D or C but do contribute minerals and the vitamins thiamine, riboflavin, and niacin. Breeding program can be expected eventually to improve the total nutritive value of wheat.

When environmental conditions permit, seeding occurs in the fail so that the roots can develop and use the warmth, moisture, and sunlight by allowing the land to remain idle for one entire growing season; a practice called fallowing. The physical and chemical properties of wheat proteins form gluten, which retains gas during fermentation. Gluten development and gas retention properties are altered by variety, soil, and growing conditions. Wheat thus differs in quality from season to season and place to place.

The leading wheat producing countries in order of output are the USSR, the United States, China, India, Canada, and Australia. The United States, however, has a higher yield per hectare than the USSR, whose geography is not ideally suited for wheat cultivation.

Wheat ground into flour and made into baked products is the form in which most wheat is consumed; however, pasta product are popular and represent an expanding market. Durum wheat is especially suitable for pasta. Puffed, flaked, and rolled wheat is used in breakfast food. A wheat food product called bulgur is prepared by cooking, dehydrating but not in eating qualities. Processed wheat germ is used in various specialty foods and to produce vitamin E.

Wheat for animal feed or pet foods is restricted because it is usually higher priced that other cereal grains of comparable nutritive value. Much wheat, however, is fed to animals in regions throughout the world where no distinction is made between food and feed grains. The by product of the flour milling operation are bran, shorts, germ, and low grade flour usually marketed as feed. Monosodium glutamate, a common condiment, is derived from gluten.

Gluten is used mainly in the bread-baking industry. Dried gluten contained 75% to 85 % protein, 5 % to 10 % lipids, and some starch. Gluten is also hydrolyzed for use as meat extenders, meat substitutes, pet foods, and food flavors. When gluten is separated from wheat, the marketing of starch becomes necessary. Wheat starch can be used for essentially all usual food and industrial purposes.

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