Cereal Grains and Pseudo-Cereals
CEREAL GRAINS AND PSEUDO-CEREALS
CEREAL GRAINS AND PSEUDO-CEREALS.
Cereals and pseudo-cereals are the primary carbohydrate supply for the world's human population. Nearly half of the annual cereal production is used for human food. Cereals also serve as the primary food for dairy and draft animals, poultry, and wild birds, and are the main ingredient in the production of alcohol. The primary cereals include wheat, rice, corn, sorghum, millets, oats, barley, and triticale. Wheat and rice provide nearly 50 percent of the world's food energy. Millet is a term that refers to small-seeded grain and has been applied to many unrelated species. The primary millet involved in world trade is proso millet, which is grown mostly in northern China. Foxtail millet and pearl millet, totally unrelated species, are also widely grown for grain on subsistence farms in Asia and Africa, respectively. Three other unrelated millets—finger, brown-top, and Japanese—are locally important cereals on subsistence farms throughout the world. Pseudo-cereals include amaranth and buckwheat.
Defining Cereals and Pseudo-Cereals
Cereals are members of the grass family (Gramineae) that are grown for their edible starchy seeds. Pseudo-cereals are grown for the same purpose, but are not members of the grass family. Since they are grouped based on use rather than the biology of the plant, this aspect will be considered separately. Initial development of cereal plants involves seminal roots that vary from three to eight in number. They arise directly from the hypocotyl. Further plant development includes the development of a second set of roots which are permanent and arise from the point just a little below the surface of the ground. These roots are fibrous rather than tap and are noted for their ability to control soil erosion through an extensive network of root hairs. They extend outward and downward in all directions from the crown, providing the primary nutrition for the plants.
Cereals are identified by alternate two-ranked leaves that are frequently formed near the ground. The leaves are composed of a sheath that encloses the stem (culm) and is split down the side opposite the blade. Identification of vegetative plants is usually based on the shape and size of the ligule, which is an appendage extending upward at the juncture of the sheath and the blade, and on the presence or absence of hairs in this region. The stems are composed of nodes and internodes that elongate to varying degrees as the crop matures. The nodes associated with leaf blades are the most apparent and are identified as the swelling in the stems. Nodes lower on the plant have the potential to develop additional stems, which are frequently referred to as tillers. The grain is produced on a spikelet that varies significantly from corn to wheat to millet in size, shape, and appearance.
The cereals and pseudo-cereals are essentially a starchy crop. However, they may contain significant quantities of protein and oil, and it is frequently these constituents that determine suitability for a specific end use. Structurally the seeds are composed of three main parts including the endosperm, embryo, and seed coat. The endosperm is the primary starch storage portion but also contains some protein. The embryo is the oil storage portion, high in protein and minerals. The seed coat, also called pericarp or bran, consists mainly of cellulose and hemicellulose with some protein and lignin. Relative proportions of the three components vary among the different cereals with the embryo of "small grains" such as wheat and barley making up less than 4 percent of the total seed, while in corn it averages 12 percent. There is also large variation from variety to variety.
Buckwheat and amaranth are two of the most widely used pseudo-cereals, but their production is dwarfed by the true cereals. Buckwheat is in the Polygonaceae family and amaranth is in the Amaranthaceae family. Neither has been the primary energy source for large regions, but both have played significant roles in food use. They both have a tap root rather than a fibrous root system and have two cotyledons rather than one as is true for the grasses. The root system consists of a tap root (central or primary root) that extends downward to a considerable distance. This root is thicker and stouter than the lateral roots that arise from it. The lateral roots may be divided several times. The tap root first penetrates the soil for some distance, forming no laterals. Laterals are then formed, beginning at the upper portion of the tap root. Buckwheat and amaranth are herbaceous, erect growing annuals. Under ordinary conditions buckwheat attains a height similar to wheat. Amaranth is typically twice the height of wheat, but there are some dwarf varieties that seldom grow taller than four feet. Both plants adjust themselves very efficiently to surroundings, such as fertility of soil and rate of seeding, by sending out branches from the main stem. The buckwheat kernel is in the form of an achene, being a single seed enclosed in an indehiscent pericarp that fits tightly around the seed. The achene is three-angled, the angles being acute, and has the form of a pyramid with the base rounded. The hull or pericarp varies from silver gray to brown or black in color and is hard and thick, with the surface polished and shining. It separates readily from the mealy endosperm. The relatively large embryo is central, dividing the soft, white endosperm into two parts, the cotyledons being broad. The surrounding testa is membranous and light yellowish-green in color.
Buckwheat groats, called kasha, are sold in whole and granulated form. Kasha can be baked, boiled, or steamed to serve as an alternative to rice and potatoes. Buckwheat flours have been used extensively in pancake mixes as well as in various breads. The Japanese mill buckwheat groats into flour for use in the production of soba noodles, a major part of the Japanese diet. Buckwheat flour is the primary ingredient in such European dishes as polenta and Zganci.
Reliance of the world population on one or more of the cereal grains as a primary food material is not just happenstance. They contain the main food essentials for the human and animal body, although they are deficient in vitamins and may be low in particular amino acid portions of the protein. Pseudo-cereals frequently have a unique amino acid profile and can be used to supplement cereals for a more balanced amino acid diet. Starch, the primary constituent of cereal grains, breaks down in the digestive tract into simpler and more easily digested sugars to supply the body with its primary source of energy. While varying in oil percentage, the oil plays a significant role in total energy supply in the diet and some varieties have been selected with amounts adequate for processing and selling as vegetable oil.
While rich in thiamine, riboflavin, niacin, and pantothenic acid, the cereals do not meet all of the vitamin and mineral requirements for food or feed. Frequently foods and feeds that are used to supplement these needs are considered more important than the cereals themselves, but as a proportion of total food and feed consumed, none come close. The role of fiber in the diet has recently been studied extensively and has altered somewhat the thought on the value of the seed coat, which contains the highest portion. This portion is also high in vitamins and minerals and many recipes have been altered to include higher proportions of whole grain or bran to take advantage of the health benefits.
Cereals and pseudo-cereals are not often used as human food without some preparation to convert them to a more edible and digestible form. Modern processing methods utilize grains to produce everything from tortillas to macaroni, as well as breakfast food, flour, bread, and vegetable spreads.
Origins of Cereals
The origins of some cereals are obscure. More than one had its cultural beginning before recorded history. The development of cereal grains, probably more than any other factor, permitted the earliest tribes to change from nomadic life to full or partial agricultural subsistence. They provided more food with less effort than did any other crop. They were important for their ability to provide subsistence and security of subsistence over time. Cereals can be easily stored to provide food between harvests. Their role in reducing the time spent by people in hunting and gathering allowed humankind to develop other pursuits.
The various cereals probably developed in different parts of the world. Corn is likely the only cereal native to the Americas, while wheat and barley may have been cultivated first in the Fertile Crescent area of the Middle East. The pseudo-cereal amaranth is also native to the Americas, and the earliest identification of amaranth as a grain comes from archaeological digs at a cave in Tehaucan, Puebla, Mexico, where seeds of Amaranthus cruentus were dated as six thousand years old. Aztec writings are the first recorded indication of its use and mention collection of large quantities of amaranth along with corn and beans in annual tribute to the ruling class. Although the origin of proso millet has not been ascertained, it is one of the first cultivated cereals, most likely prior to wheat. Proso millet has been known for many thousands of years in eastern Asia including China, India, and Russia. The genus Setaria is widely distributed in warm and temperate areas. Foxtail millet, the most widely grown food of this genus, is one of the world's oldest cultivated crops. Its planting was mentioned in Chinese records as early as 2700 B.C.E. Foxtail was the most important plant food in the Neolithic culture in China, and its domestication and cultivation constituted the earliest identifiable manifestation of this culture, the beginning of which has been estimated at over four thousand years ago. Buckwheat is native to temperate east Asia, where it was grown in China before 1000 C.E.
Modern Cereal Production
Development of mechanization for planting, harvesting, shipping, and processing of cereals during the first half of the twentieth century led to the greatest advancement in cereal production since the dawn of history. Practically all labor involved in modern cereal production involves mechanized operation. Mechanization—along with improvements in weed, disease, and insect control, improved nutrient management, and variety improvements—increased production potential and led to the Green Revolution in the second half of the twentieth century. Today, one farmer typically provides cereals that feed more than one hundred people. The average yield per unit of land of cereals has increased by more than 50 percent in the last fifty years. Increases in corn and rice have been more dramatic than those of the other cereals, but all have shown steady improvements. The dramatic yield improvements in corn have led to a production area increase in corn at the expense of oats, millet, rye, and barley. Especially in China, millet production has been pushed to more marginal areas with the best land being dedicated to corn and rice, with higher yield potential.
The sickle or reaping hook was used for cutting cereals during the Stone Age. In biblical times the blades were made of bronze or iron. Steel sickles were made in the nineteenth century. The sickle is still a part of harvesting in many developing countries. Typically a man with a sickle can cut, bind, and shock an acre of grain in around forty hours. A scythe was more common in the Roman Empire and areas of the Orient. With attached cradle frames, harvesting time was cut to twenty hours per acre. In the first century of the common era, Pliny the Elder described a grain stripper that was pushed by oxen and used by inhabitants of Gaul. Between 1775 and 1840 reapers were developed in Europe and the United States, but this was quickly replaced by combines by 1950. The combine not only replaced the reaper, but also replaced the thresher that was developed in the latter half of the nineteenth century. Before then, grain had been flailed out by hand or threshed by treading out the grain under the feet of people or livestock. With a flail a man can thresh seven or eight bushels per day. A form of threshing machine still used in Asia and Africa consists of stone-studded planks, stone rollers, or metal disks on a shaft drawn by animals over the grain stalks that are spread on a threshing floor. Today, modern combines cut, thresh, and clean more than one hundred acres per day.
The mechanical corn picker was not developed until World War II and replaced the age-old tradition of husking by hand from the standing stalk. If the stalks were being harvested for forage, some cut them by hand and placed them in shocks to cure. Today the corn picker has been replaced by the modern combine used on other small grains with only modifications of the header.
Storage and Transportation
Compared with many other crops, cereals and pseudo-cereals are extremely amenable to storage. The moisture content at harvest is typically below 15 percent and their composition and seed coats are such that deterioration is slow. Seasonal harvest with a continuous demand means that storage between harvests is required. Under typical conditions this need can be met easily; with care, storage for many years without serious loss of quality is possible. Storage during times of surplus is a part of human history, and with benefits of modern technology, cool dry conditions can be maintained and storage can be successful for extended periods of time. There are, however, problems with storage, including excessive moisture content at the time of storage, excessive temperature, microbial, insect, and arachnid infestation, rodent and bird predation, mechanical damage, and biochemical deterioration. The latter is especially important for cereals and pseudo-cereals with higher than normal oil content because the oil becomes rancid over time.
The distribution system for cereals is frequently criticized as there is a surplus of production and yet hungry people around the world. However, the infrastructure that moves cereals by truck, train, barge, and ship is one of the most complex and efficient systems in the world. It is estimated that rail shipments from Kansas and Nebraska—the heart of winter wheat production—to the Pacific Coast, or a combination of truck and barge shipments to the Gulf Coast, cost less than $0.50 per bushel, including less than $0.15 for transportation from the field to a local destination, and that loading on a ship and delivering to a handling facility in Southeast Asia or Africa adds only $0.50 per bushel. Getting from one village of the developing world to the next can double the total value of the wheat.
Cereals are processed in many ways, but the methods are broadly grouped into wet milling, dry milling, oil processing, fermentation, and feed processing. Characteristic features of milling processes include separation of the endosperm from the embryo and seed coat, and reduction of the endosperm into flour or grits. Milling schemes are classified as wet or dry, but this is a relative classification because water is used in almost all separations. Few generalizations can be made about cereal milling. For example, most rice is milled in two stages to remove the husk and then the bran, however, some is milled into flour. There are dry milling processes that change the shape and size of cereal. Fractions produced by this step are frequently separated in another step. An additional milling process can be completed by changing the temperature or water content. Unlike dry milling, which primarily just fractionates, wet milling is a maceration process in which physical and chemical changes occur in the basic constituents: starch, protein, and cell wall material. The objective is complete dissociation of the endosperm cell contents with the release of the starch granules from the protein network. Processing has taken a huge step from Stone Age grinding stones for dry milling to soaking processes to remove starch, described by Cato in the second century B.C.E., to modern milling and extrusion processes. Milling processes today are almost entirely based on meeting end product specifications by the most efficient means possible with almost all steps controlled mechanically and electronically.
The other primary processing method is production of alcohol from cereal grains through a fermentation process. This two-step process includes the conversion of starch to soluble sugars by amylolytic enzymes, followed by the conversion of the sugars into alcohol. In the first step the enzymes may be derived from the grain itself (malting), from other organisms present or added as extracts. The malting process has also been used for the production of some breakfast foods. It is comprised of a controlled germination during which enzymes capable of catalyzing hydrolysis of starch are produced. The fermentation process results in the development of alcoholic drinks, including beer and sake. Further processing by evaporating and condensing increases the alcohol content and produces whiskey, scotch, bourbon, and neutral spirits, including those used for production of fuel. Today production of gasohol ranks as one of the largest uses of corn following its use as animal feed. The by-products of fermentation are primarily used as livestock feed.
The number of foods prepared from a base of cereals is the largest of all food crops. Cereal grains are largely interchangeable for different uses and are, therefore, mutually competitive. They can substitute for one another in a number of food and nonfood uses. In their use as feeds they are almost completely interchangeable. That allows more latitude within which available grain supplies can satisfy a series of demands.
As raw materials in major processing industries, however, grains are not always so interchangeable. Technology of a particular process often requires a specific combination of chemical and physical characteristics in the raw material, which can be met fully by only one type of grain. This has been extended to variety specificity for many products and has led to the development of identity-preserved marketing systems that are quite distinct from the bulk transportation systems discussed earlier. Some predict that with greater use of biotechnology for adding trait specificity, the identity-preserved marketing systems may become increasingly important.
Cereal uses for food are largely defined by cultural context, but with the greater global movement of people, there is now a greater dispersion of foods. For example, rice-based products are now a common food item in places with no rice production. The same is true of amaranth.
The Aztecs used amaranth, which they called huautli, in a beverage, a sauce, for a type of tortilla, and for various medical uses. Popped or ground amaranth often was mixed with honey or other sweet, sticky plant materials, and then shaped into a variety of figures and shapes that were used in celebrations and religious ceremonies. Unlike most cereals, amaranth leaves are used as a vegetable, similar to spinach, and certain types have been selected almost exclusively for their leaf production. Most commercial production of amaranth is for types selected primarily for grain or forage production.
Both cereals and pseudo-cereals have a long history of use as forage crops for livestock. The small grains have been used extensively for hay, grazing, green-chop (fresh fodder harvested and used as cattle feed), and silage. Foxtail millet, pearl millet, and some other millets are perhaps better known for their forage use than for their grain production. Corn and sorghum are utilized extensively for silage. Almost all stover of all cereals and pseudo-cereals has potential utilization by livestock even though it may require supplementation with higher-protein feeds. Prior to the soft dough stage, when the kernel is still immature and has not yet hardened, most cereals meet or exceed nutrient requirements of livestock. Cereal forages are used as supplemental feed for cow and calf herds, support major elements of the stocker cattle industry, and have potential to produce finished beef. Cereal improvement programs, while directed at improved seed production, have improved disease resistance, stress resistance, insect resistance, and general adaptability to specific climates. This has led to significant improvements in consistency and quantity of forage production as well.
Cereal silage is an important part of the dairy industry. Corn silage alone makes up over 40 percent of the value of the forage fed to dairy cows in the United States. Corn silage is noted for its palatability, consistent quality, high yields, and energy content compared with alternative forages. The cost of production tends to be lower for corn silage than for most other forages, but this is partially offset by the large transportation costs of relatively wet material. Transportation costs have largely limited use to livestock production near the field from which the silage was harvested.
While the cereals and pseudo-cereals are primarily known as a source of energy, they have played important roles in other ways throughout history. Cereal sprouts have long been known for their cleansing properties and are a common part of health food stores. Amaranth and buckwheat have been evaluated extensively for their vitamin E, B1, and B2 activity in reducing arteriosclerosis. Oats and buckwheat are recognized as cholesterol-lowering foods. The pseudo-cereals have a different amino acid composition than the cereals and when combined in the diet produce a much more ideal amino acid balance.
Perhaps because of their importance in meeting daily sustenance and perhaps for other reasons, the cereals have been a symbol of human life and culture throughout recorded history. Amaranth played a major role in pagan rituals. Wheat and wheat harvesting are a part of world symbolism from the flags of major countries to churches and cemeteries. So much emphasis was placed on grain production by Roman peoples that the protection of grain was the primary concern of Ceres, one of the powerful Roman goddesses. The name cereal was derived from this association. With the huge supply of human energy coming from a few major cereals, and a few minor cereals in some regions, one of the big concerns for the world population is the risk of a major crop failure. This possibility has received increasing attention as selection and major gene improvements have narrowed the genetic base within crops to a few major varieties. It is particularly important that the diversity within major crops is conserved effectively, available for use, and managed wisely.
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David D. Baltensperger
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