Cereal Grain Structure and Composition
1. Cereal grains
The edible fruits of cereal grasses are botanically called caryopses. In food science and agriculture, they are commonly referred to as cereal grains.
2. Main parts of a cereal grain
A typical cereal grain consists of three major anatomical regions: bran or outer layers, endosperm, and germ (embryo). Their proportions differ among cereal species.
3. Endosperm
The endosperm is usually the largest component of a cereal grain. It contains mainly starch and storage proteins and provides nutrients for the developing embryo during germination.
4. Bran and seed coverings
The outer grain tissues include the pericarp, seed coat, nucellar layer, and aleurone layer, depending on the cereal. These tissues are commonly grouped with the bran fraction during milling.
5. Wheat grain
Wheat grain is a caryopsis composed mainly of bran, endosperm, and germ. The endosperm represents most of the grain and is the principal source of refined wheat flour.
6. Wheat endosperm
Wheat endosperm contains starch granules embedded in a protein matrix. The interaction between starch and storage proteins influences flour quality, dough development, and baking performance.
7. Maize kernel
The maize kernel consists principally of pericarp, aleurone, endosperm, and germ. The endosperm contains most of the starch, whereas the germ is relatively rich in oil.
8. Carbohydrates in cereals
Carbohydrates are the major components of cereal grains. Starch is generally the predominant carbohydrate, while sugars and non-starch polysaccharides occur in smaller amounts. Cereal composition varies among species and cultivars.
9. Dietary fibre in cereals
Cereal dietary fibre includes non-digestible components such as cellulose, hemicelluloses, arabinoxylans, β-glucans, and resistant starch, depending on the analytical definition. Ordinary digestible starch is not classified as dietary fibre.
10. Fibre-rich cereal grains
Whole grains generally contain more dietary fibre than refined grains because the bran and germ are retained. Whole wheat and several millets can provide substantial dietary fibre, but the exact concentration depends on variety and processing.
Cereal Proteins and Lipids
11. Protein in rice
Rice generally has a lower protein concentration than several other major cereals, although the amount varies with cultivar, growing conditions, and degree of milling. Rice protein is concentrated differently among the bran, germ, and endosperm.
12. Distribution of protein
Protein is not uniformly distributed throughout cereal grains. The aleurone layer and germ generally contain higher concentrations of protein and minerals, while the starchy endosperm contains most of the grain’s starch.
13. Major cereal protein classes
Cereal proteins are traditionally classified according to solubility as albumins, globulins, prolamins, and glutelins. Their proportions vary considerably among cereals.
14. Gluten proteins
In wheat, gliadins and glutenins are the principal storage proteins responsible for gluten formation. They interact with water and mechanical mixing to produce the viscoelastic gluten network.
15. Gluten functionality
Gliadins contribute mainly to dough extensibility and viscosity, whereas glutenins contribute strongly to elasticity and dough strength. The combined gluten network is important in bread-making.
16. Cereal protein quality
Cereal protein concentration varies widely among species and cultivars. Cereal proteins are commonly limited by lysine, making cereal-legume combinations nutritionally complementary in many diets.
17. Lysine limitation
The original statement that cereals are both “deficient in lysine” and “rich in lysine” is incorrect. In general, cereal proteins contain relatively low amounts of lysine compared with human amino-acid requirements.
18. Cereal lipids
Cereal lipid content varies among species. Wheat and rice generally contain relatively low lipid concentrations, whereas maize and oats contain comparatively more. Cereal lipids include triglycerides, phospholipids, glycolipids, and other minor lipid components.
19. Distribution of lipids
Lipids are concentrated particularly in the germ and outer grain layers, while the starchy endosperm generally contains less lipid. Lipid distribution affects milling, nutritional value, and storage stability.
Minerals, Vitamins and Enzymes
20. Minerals in cereal grains
Cereals contain minerals including phosphorus, potassium, magnesium, calcium, iron, zinc, and manganese. Mineral concentration varies with species, cultivar, soil, agricultural conditions, and processing.
21. Phytate
Phytate is an important storage form of phosphorus in cereal grains. It can bind minerals such as iron, zinc, calcium, and magnesium, thereby reducing their bioavailability under some dietary conditions.
22. Calcium and iron
Cereals are not generally considered rich sources of highly bioavailable calcium. Iron is present in cereal grains, but its absorption may be reduced by phytate and other dietary components.
23. Finger millet
Finger millet (Eleusine coracana) is relatively rich in calcium compared with many other cereals. However, its mineral bioavailability depends on factors including phytate content and processing.
24. Parboiling and nutrient migration
During rice parboiling, water-soluble nutrients from the outer grain layers can migrate into the endosperm. This can improve retention of certain nutrients after milling compared with similarly milled raw rice.
25. Vitamins in cereals
Most cereal grains are poor natural sources of vitamin C and preformed vitamin A. Some cereals, particularly yellow maize, contain carotenoids, including provitamin A carotenoids. Cereal grains are important sources of several B vitamins and vitamin E, although concentrations vary.
26. Cereal enzymes
Important cereal enzymes include amylases, proteases, lipases, phytases, lipoxygenases, and oxidoreductases. They influence germination, malting, dough properties, lipid stability, and grain deterioration.
Grain Quality and Rice Technology
27. Thousand-grain weight
Thousand-grain weight is a useful physical quality parameter indicating kernel size and grain development. It is influenced by genotype, growing conditions, maturity, and grain filling.
28. Bulk density
Bulk density is the mass of a quantity of grain divided by the total bulk volume occupied by that grain, including the spaces between kernels. It is important in storage, transport, handling, and equipment design.
29. Moisture of harvested paddy
Freshly harvested paddy may have relatively high moisture content, often around 18–25% wet basis, depending on cultivar, harvest maturity, weather, and harvesting conditions. This is a typical range rather than a universal value.
30. Drying for storage
Paddy must be dried to a moisture level appropriate for its intended storage conditions. A moisture content around 12–14% is commonly associated with safe storage of properly dried rice under suitable conditions, but the appropriate target depends on storage temperature, duration, relative humidity, grain condition, and storage system.
31. Rice husk
Rice husk is the outer protective covering removed during milling. It commonly represents approximately one-fifth of paddy mass, although the proportion varies among rice varieties and processing conditions.
32. Silica in rice husk
Rice husk is rich in silica, and rice-husk ash can contain a high proportion of silica when produced under controlled combustion conditions. Exact silica concentration depends on the raw material and combustion process.
33. Rice bran
Rice bran is a valuable milling by-product containing lipids, protein, dietary fibre, minerals, vitamins, and bioactive compounds. It can deteriorate rapidly because endogenous lipase activity promotes hydrolysis of bran lipids.
34. Rice-bran composition
Rice-bran composition varies with rice variety and milling degree. It is generally richer in protein and lipid than milled rice, but fixed percentages should not be treated as universal values.
35. Rice parboiling
Parboiling is a hydrothermal treatment involving soaking, heating or steaming, and drying before milling. It causes important physical and structural changes, including partial or substantial gelatinization of starch.
36. Effects of parboiling
Parboiling can increase kernel strength, reduce some milling losses, alter cooking properties, and improve retention of certain water-soluble nutrients after milling. The extent of these effects depends on the parboiling process.
Wheat, Maize, Barley and Oats
37. Wheat classification
Wheat may be classified according to species, kernel hardness, protein content, color, growing season, and end use. Hard and soft wheat differ in milling characteristics, while strong and weak wheat primarily describe flour and dough performance.
38. Wheat hardness
Wheat hardness is associated with the physical structure of the endosperm and the strength of interactions between starch granules and the surrounding protein matrix. It affects milling energy, flour particle size, and flour functionality.
39. Maize
The scientific name of maize is Zea mays L. Maize is cultivated worldwide for food, animal feed, starch, oil, bio-based products, and industrial applications.
40. Maize germ
The maize germ is relatively rich in lipids and protein compared with the starchy endosperm. It is an important raw material for maize-germ oil production.
41. Barley
Barley (Hordeum vulgare) is used for foods such as pearled barley and barley flour and is also widely used for malting and brewing.
42. Oat grain
The oat grain consists of an outer hull surrounding the edible groat. The groat contains bran/aleurone tissues, germ, and endosperm.
Oats, Millets and Cereal Products
43. Commercial oat products
Important oat products include oat groats, rolled oats, oat flakes, oat flour, oat bran, quick oats, and instant oat products. Processing can include dehulling, kilning, steaming, cutting, rolling, and grinding.
44. Oat groats
Oat groats are the dehulled oat kernels. They contain the principal edible components of the grain and can be further processed into flakes, flour, and other products.
45. Major millet species
Important millet species include pearl millet, finger millet, foxtail millet, proso millet, kodo millet, barnyard millet, and little millet. Scientific names and common names should be checked against the relevant taxonomic authority because nomenclature can change.
46. Millets and sorghum
Millets are a group of small-seeded cereal grasses. Sorghum is a cereal grain but is generally classified separately from the millets, although both are important crops in dryland agriculture.
47. Barley malting
Malting involves controlled germination followed by drying or kilning. During germination, enzymes such as amylases and proteases develop and modify the grain. Barley malt is particularly important in brewing.
48. Breakfast cereals
Ready-to-eat breakfast cereals include flakes, puffed cereals, shredded cereals, granulated products, and extruded cereals. Processing may involve cooking, extrusion, flaking, puffing, drying, toasting, and coating.
49. Cereal puffing and extrusion
Puffing and extrusion can produce expanded cereal products through rapid moisture vaporization and structural expansion. Expansion is influenced by moisture content, starch properties, temperature, pressure, formulation, and processing conditions.
50. Dietary fibre in oats
Oats are an important source of β-glucan, a soluble dietary fibre concentrated mainly in the cell walls of the oat endosperm and aleurone. Oat hulls contain substantial structural fibre, but hull fibre should not be equated with the dietary-fibre content of the edible oat groat.
INTERNATIONAL AND NATIONAL STANDARDS
Codex Alimentarius
Codex is the appropriate international reference system for many cereal commodities. Current Codex standards include:
- CXS 152-1985 — Standard for Wheat Flour
- CXS 153-1985 — Standard for Maize (Corn)
- CXS 155-1985 — Standard for Degermed Maize Meal and Maize Grits
- CXS 169-1989 — Standard for Whole and Decorticated Pearl Millet Grains
- CXS 172-1989 — Standard for Sorghum Grains
- CXS 173-1989 — Standard for Sorghum Flour
- CXS 178-1991 — Standard for Durum Wheat Semolina and Durum Wheat Flour
- CXS 198-1995 — Standard for Rice
- CXS 199-1995 — Standard for Wheat and Durum Wheat
The Codex list shows that these are commodity-specific standards rather than one universal specification for all cereals.roducts.
