Module 1. Cereal grains, legumes and oilseeds

Lesson 1

INTRODUCTION TO CEREAL GRAINS, LEGUMES AND OILSEEDS, STRUCTURE AND COMPOSITION OF CEREAL GRAINS, LEGUMES AND OILSEEDS

1.1 Introduction

India has reached to a level of self-sufficiency in the production of cereals, pulses and oilseeds after the green revolution. Cereals are plants which yield edible grains and includes rice, wheat, corn, barley, and oats. Cereal grains are the fruit of plants belonging to the grass family (Gramineae). Cereal grains provide the world with majority of its food calories and about half of its protein. They are also good source of micronutrients such as calcium, iron and vitamins of group B. Cereals are staples and are consumed in large quantities by majority of population in the world either directly or in modified form as major items of diet such as flour, bran and numerous additional ingredients used in the manufacture of other foods. Asia, America, and Europe produce more than 80 percent of the world’s cereal grains. Cereals are easy to store because of low moisture content, easy to handle and providing variety to the diet. The principle cereal grains grown in India are wheat, rice, corn, sorghum and barley.

Legumes are next to cereals as an important source of proteins. They are flowering plants having pods which contain bean or peas. There are basically two groups of legumes. First is high-protein high-oil group like soybean, groundnut, lupine, etc. which are mainly used for processing and contains high protein (~ 35%) and oil content (15- 45%). The second group comprises the moderate- protein low-oil types like cowpea, gram, pea, lentil etc. India is one of the largest pulse growing countries in the World. Different pulses grown in India are chickpea (bengal gram/chana), pigeon pea (tur/arhar), green gram (moong), black gram (urad), lentils (masur).

Oilseeds have become an increasingly important agriculture commodity, with a steady increase in annual production worldwide. Oilseeds are seeds which contain high oil content and are widely grown as a source of edible oil. Major oilseeds grown in India are groundnut, cottonseed, mustard, rapeseed, soybean, sunflower and sesame seed. The coconut (copra) is also an important oilseed.

Cereal grains are not only low in protein but also deficient in certain essential amino acids, especially lysine. Legumes as well as many oilseeds are rich in lysine, though relatively poor in methionine. Edible oilseed meals obtained from oilseeds are rich in proteins and have been used to improve the nutritional properties of cereal products such as infant food and food for school going children in most of the countries in world.

1.2 Cereal Grains

1.2.1 Rice

Rice (Oryza sativa, Linn.) crop originated in Asia and has been a staple food there since the Ice Age in the North. The geographical site of original rice domestication is yet not sure. But according to a general consensus, domestication occurred at three places – India, Indonesia and China – thereby giving rise to three races of rice – Indica, Javonica and Sinica (also known as Japonica), respectively. Actual rice grains and husk have been excavated in India that were more than 4500 years old and in China more than 5000 years. According to ancient Greek writers, rice penetrated Europe around 3000 B.C., having been brought from India by Alexander the Great.

1.2.2 Wheat

Historic documents confirm that wheat (Triticum aestivum, Triticum durum) is the earliest field crop used for human food processing. The cultivation of wheat reaches far back into history as it was predominat source of food for Human. The precise origin of the wheat cultivation is unclear, but it is thought that man has been cultivating and processing the wheat for at least 12,000 – 17,000 years.

1.2.3 Corn

Corn or Maize (Zea mays, L) is native to the America. Corn originated in Mexico, evolving from the wild grass Teosinte. Archeological evidence suggests that corn was domesticated and grown as early as 5000 B.C. in Mexico. Following Columbus’s discovery of America, corn was transplanted to Spain from where it quickly spread across Europe, Africa and Asia.

1.2.4 Barley

Barley (Hardeum vulgare L.) is among the most ancient of the cereal crops. The original area of cultivation has been reported to be in the Fertile Crescent of the Middle East, in present day Lebanon, Iran, Iraq, and Turkey. There is now considerable evidence that barley was under cultivation in India and China considerably later then in Middle East. Barley played an important role in ancient Greek culture as a staple bread–making grain, as well as an important food for athletes, who attributed much of their strength to their barley–containing training diets. Gladiators were known as hordearii, which means “eaters of barley”. In almost every culture through the ages, barley foods are described as having almost mystical properties, and barley is often referred to as the “king of grains”.

1.3 Structure of Cereal Grains

Cereal grains are the fruit of plants belonging to the grass family (Gramineae). Botanically, cereal grains are a ‘dry’ fruit called a caryopsis. (Fig. 1.1: Wheat ; Rice ; Corn ; Barley)

The caryopsis fruit has a thin, dry wall which is fused together with the seed coat. Kernel structure is important with respect to minimizing damage during grain harvest, drying, handling, storage, milling, and germination and in enhancing nutritional value. There are a few important structural features that the cereal grains have in common. All of the cereal grains are plant seeds and contain three distinct anatomical portions – a large centrally located starch endosperm, which also is rich in protein, protective outer layers such as hull and bran, and an embryo or germ.

The seed portion of cereals consists of numerous components which basically include three parts: a seed coat or testa (bran), storage organ or nutritive reserve for the seed (endosperm), and a miniature plant or germ. The fruit tissue consists of a layer of epidermis and several thin inner layers a few cells thick. The aleurone layer which is just below the seed coat, is only a few cells thick, but is rich in oil, minerals, protein and vitamins. Starch and protein are located in the endosperm which represents the bulk of the grain and is sometimes the only part of the cereal consumed. Starch is arranged in the form of sub-cellular structures called granules that are embedded in a matrix of protein. The developing endosperm contains protein bodies which become a continuous phase as the grain matures. There is generally a gradient of more protein and less starch per cell from the outer to the inner region of the endosperm. The diameter, shape, size distribution and other characteristics of starch granules vary with different cereals. Starch granules range in size from 3-8 µm in rice; 2-30 µm in corn, and 2-55 µm in wheat. Reserve proteins in the endosperm are in the form of smaller ‘protein bodies’ that range in size from 2-6 µm that become disordered and adhere to the starch granules in the mature grain of species like wheat.

1.4 Chemical Composition of Cereals

Cereals are of plant origin which yield edible grains which are consumed directly or in modified form as major part of diet and also feed to livestock. Rice and wheat are most important cereals forming part of human food. The major constituents of the principal cereals are listed in Table 1.1. Cereal grains consist of about two third carbohydrates, mainly in form of digestible sugars and starches. These grains are also an important source of several other nutrients such as protein, calcium, iron, vitamin B complex and dietary fiber. Cereal grains contain 10-14% moisture, 58-72% carbohydrate, 8-13% protein, 2-5% fat and 2-11% indigestible fiber. They also provide about 300-350 kcal/100 g of grains. Cereals are deficient in vitamins A, D, B₁₂ and C.

Table 1.1 Proximate compositions of cereal grains

Cereal	Moisture %	Carbohydrates %	Protein %	Fat %	Fiber %	Ash %	Calorific value (kcal/100 gm.)
Wheat (Triticum aestivum, Triticum durum)	11	69	13	2	3	2	340
Rice (Oryza sativa, L.)	11	65	8	2	9	5	310
Corn (Zea mays, L.)	11	72	10	4	2	1	352
Sorghum (Sorghum bicolor L.)	11	70	12	4	2	1	348
Barley (Hardeum vulgare L.)	14	63	12	2	6	3	320
Oats (Avena sativa)	13	58	10	5	10	4	317
Rye (Secale cereale)	11	71	12	2	2	2	321

1.5 Structure of Legumes

The term ‘pulses’ is limited to crops harvested solely for dry grain, thereby excluding crops harvested green for food mainly as vegetables (peas, beans, etc.), crops used mainly for oil extraction (e.g. soybean and groundnut) and leguminous crops for sowing purpose (e.g. seeds of clover and alfalfa). A legume is a plant in the family Fabaceae (or Leguminosae), or a fruit of these specific plants. A legume fruit is a simple dry fruit that develops from a simple carpel and usually dehisces (opens along a seam) on two sides. A common name for this type of fruit is a pod. Well-known legumes include peas, beans, lentils, black gram, green gram, soy and groundnut.

Pulses all have a similar structure, but differ in color, shape, size, and thickness of the seed coat. Mature seeds have three major components: the seed coat, the cotyledons, and the embryo (Fig. 1.2).

The seed coat or hull accounts for 7–15% of the whole seed mass. Cotyledons are about 85% of the seed mass, and the embryo constitutes the remaining 1–4%. The external structures of the seed are the testa (i.e., seed coat), hilum, micropyle, and raphe. The testa is the outer most part of the seed and covers almost all of the seed surface. The hilum is an oval scar on the seed coat where the seed was attached to the stalk. The micropyle is a small opening in the seed coat next to the hilum. The raphe is a ridge on the side of the hilum opposite the micropyle.

When the seed coat is removed from grain, the remaining part is the embryonic structure. The embryonic structure consists of two cotyledons (or seed leaves) and a short axis above and below them. The two cotyledons are not physically attached to each other except at the axis and a weak protection provided by the seed coat. Thus the seed is unusually vulnerable to breakage.

The outermost layer of the seed coat is the cuticle, and it can be smooth or rough. Both the micropyle and hilum have been related to the permeability of the testa and to water absorption.

Fig. 1.2 Structure of pulse

1.6 Composition of Pulses

Pulses contain carbohydrates, mainly starches (55-65 percent of the total weight); proteins, including essential amino acids (18-25 percent, and much higher than cereals); and fat (1 - 4 percent). The remainder consists of moisture, fiber, minerals and vitamins. The composition of protein, fat, minerals, fibre, carbohydrates, minerals and vitamins etc of different pulses is given in Table 1.2.

Table 1.2 Proximate composition of pulses (Per 100 g edible portion)

Pulse	Scientific name	Composition /100 g edible portion
		Moisture	Protein	Fat	Carbohydrates	Minerals	Fiber	Energy (Kcal)
Tuver (Red gram, Pegion pea)	Cajanus cajan	13.4	22.3	1.7	57.6	1.7	1.5	335
Bengal gram (Chick pea)	Cicer arietinum L.	9.8	17.1	5.3	60.9	3.0	3.9	360
Val papdi (Field bean)	Dolichos lablab	9.6	24.9	0.8	60.1	3.2	1.4	347
Moong (Green gram)	Phaseolus aureus Roxb	10.4	24.0	1.3	56.7	3.5	4.1	334
Kulad (Horse gram)	Dolichos biflours	11.8	22.0	0.5	57.2	3.2	5.3	321
Masoor (Lentils)	Lens esculenta	12.4	25.1	0.7	59.0	2.1	0.7	343
Udad (Black gram)	Phaseolus mungo	10.9	24.0	1.4	59.6	3.2	0.9	346
Chowli (Cow peas)	Vigna catjang	13.4	24.1	1.0	54.5	3.2	3.8	323
Vatana (Peas)	Pisum sativum	16.0	19.7	1.1	56.5	2.2	4.5	315

1.7 Structure of Oilseeds

Oil seeds are mainly used for extraction of edible oil. Oilseeds crops grown in India are groundnut, rapseed, mustard, soybean, sunflower, sesame, castor, safflower, niger and linseed. Oilseeds are made up of three basic parts: the seed coat, the embryo, and one or more food storage structures. The seed contains two pieces of cotyledons that function as food reserve structures. The seed coat is marked with a hilum or seed scar. The basic function of the coat is to protect the embryo from fungi and bacterial infection.

Unlike seeds of grass family (e.g. wheat, rice, etc.), where oil is concentrated in a germ that lies along the side of the endosperm, the entire hull of oilseeds is the germ. It typically consists of a rootlet (hypocotyl) and two cotyledons leaves (Fig. 1.3) that are pushed above the soil and unfold during the germination. Oil in oilseed is distributed in spheresomes throughout the germ cells. Recovery of oil from oilseeds is facilitated by rupturing the cell walls by heat and pressure during flaking, and by optional extrusion, followed by pressing or solvent extraction. Waxes from the pericarp (hull), which protect the seed against drying are often also solubilized by the sovent or oil. 

Fig 1.3 Structure of oilseed

1.8 Composition of Oilseeds

Proximate composition of various oilseeds grown in India is given in Table 1.3.

Table 1.3 Proximate composition of whole oilseeds (%)

Oilseed	Scientific name	Moisture	Protein	Fat, EE*	Crude fiber	Ash
Soybean (Whole seed)	Glycine max	10.0	36.3	18.9	5.0	4.4
Groundnut (Shelled kernel)	Archis hypogea	10.0	26.0	45.0	4.0	2.5
Corn germ (Dry milled)	Zea mays, L	10.0	13.0	22.5	4.5	2.5
Sunflower seed, oil-type (Whole seed)	Helliathus annus	10.0	21.0	42.0	19.0	4.5
Cotton seed (Cottonseed with linters)	Gossypium hirsutum L.	10.0	22.0	19.5	19.0	4.5
Rapeseed/Canola (Whole seed)	Brassica juncea	8.0	22.0	41.0	10.0	5.0

EE*- Ether extract

Glossary

· Monocotyledons, also known as monocots, are one of two major groups of flowering plants (or angiosperms) that are traditionally recognized, the other being dicotyledons, or dicots. Monocot seedlings typically have one cotyledon (seed-leaf), in contrast to the two cotyledons typical of dicots

· Poaceae (also known as the Gramineae) is a large and nearly ubiquitous family of monocot flowering plants. Members of this family are commonly called (land) grasses.

· Caryopsis is a type of simple dry fruit — one that is monocarpelate (formed from a single carpel) and indehiscent (not opening at maturity) and resembles an achene, except that in a caryopsis the pericarp is fused with the thin seed coat.

· The caryopsis is popularly called a grain and is the fruit typical of the family Poaceae (or Gramineae), such as wheat, rice, and corn.

· Husk (or hull) in botany is the outer shell or coating of a seed. It often refers to the leafy outer covering of an ear of maize (corn) as it grows on the plant. Literally, a husk or hull includes the protective outer covering of a seed, fruit or vegetable.

· Endosperm is the tissue produced inside the seeds of most flowering plants around the time of fertilization. It surrounds the embryo and provides nutrition in the form of starch, though it can also contain oils and protein. This makes endosperm an important source of nutrition in human diet. For example, wheat endosperm is ground into flour for bread (the rest of the grain is included as well in whole wheat flour), while barley endosperm is the main source for beer production.

· Germ of a cereal is the reproductive part that germinates to grow into a plant; it is the embryo of the seed. Along with bran, germ is often a by-product of the milling that produces refined grain products. Cereal grains and their components, such as wheat germ, rice bran, and maize may be used as a source from which vegetable oil is extracted, or used directly as a food ingredient. The germ is retained as an integral part of whole-grain foods

· Bran is the hard outer layer of grain and consists of combined aleurone and pericarp. Along with germ, it is an integral part of whole grains, and is often produced as a by-product of milling in the production of refined grains. When bran is removed from grains, the grains lose a portion of their nutritional value. Bran is present in and may be milled from any cereal grain, including rice, corn (maize), wheat, oats, barley and millet. Bran should not be confused with chaff, which is coarser scaly material surrounding the grain, but not forming part of the grain itself. Bran is particularly rich in dietary fiber and essential fatty acids and contains significant quantities of starch, protein, vitamins and dietary minerals.