The Importance of Cereal Proteins in Daily Nutrition

Cereals stand as a vital source of energy, packing approximately 350 kcal per 100 grams. In many regions, including India, they contribute significantly to daily caloric intake, with cereals and grain legumes accounting for 70% to 90% of daily calories. Furthermore, they provide a substantial portion of dietary protein, although their protein quality varies.

Unfortunately, cereal proteins are often lacking in essential amino acids, particularly lysine. Maize, in particular, is deficient in both lysine and tryptophan, a precursor to niacin. This deficiency underscores the importance of a mixed diet containing diverse proteins to meet nutritional needs adequately.

Among cereals, rice stands out for its relatively higher lysine content compared to others. This makes rice protein comparatively better in quality. Additionally, rice is a notable source of B-group vitamins, especially thiamine. However, it lacks vitamins A, D, C, and is relatively poor in calcium and iron.

As our understanding of nutrition evolves, efforts are underway to enhance the quality of cereal proteins through breeding and biotechnological interventions. While cereals remain a staple in many diets worldwide, optimizing their nutritional content remains a priority for ensuring overall health and well-being.
The Importance of Cereal Proteins in Daily Nutrition

Protein in amaranth grain

Amaranth is native to Mexico and Central America. These grains were once considered a staple food in the Inca, Maya and Aztec civilizations. And it remains a part of the Central American diet. Amaranth has increased in popularity throughout the U.S. as more people have become aware of its impressive nutritional profile.

Amaranth is rich in protein, with nearly double the amount found in corn or rice. One of the primary functions of protein is to maintain and repair muscle tissue in the body.

One cup (246 grams) of cooked amaranth contains about 9.3 grams of protein. The protein is easily absorbed by the body and contains all amino acids — even lysine, which is often missing from cereal grains. Amaranth tops the list of the grains with the most lysine, providing 721 milligrams per 1/2-cup serving.

Studies have shown that, in the plant kingdom, amaranth proteins are among the most similar to animal proteins. As a complete source of protein, this grain includes all nine essential amino acids, along with lunasin, a peptide believed to have anti-inflammatory benefits. Lunasin, a naturally occurring peptide in soybeans classified as a 2S albumin, has 43 amino acids with a molecular weight of 4.7 kDa.

Lunasin appears to prevent normal cells from turning into cancer cells. Lunasin might also decrease the amount of cholesterol made by the body.
Protein in amaranth grain

Soft wheat flour - has a lower gluten content

Bakers generally classify wheat by the hardness of the kernel, that is, by whether the kernel is hard or soft. Hard wheat kernels are high in protein; soft wheat kernels are low in protein.

Flour is the product obtained by grinding wheat kernels or “berries.” Flours milled from soft wheat kernels are whiter in color and finer to the touch than hard wheat flours.

Soft wheat flour is comparatively low in gluten and so results in a finer texture. Soft flour is usually divided into "cake" flour, which is the lowest in gluten, and "pastry" flour, which has slightly more gluten than cake flour.

It produces more tender products, and this is desirable for many in cakes, pastries, cookies, crackers, oriental noodles and pastries. Flour with low protein content, low ash content, and weak gluten characteristics makes good quality sponge cake.

Cake flour has a greater percentage of starch and less protein, which keeps cakes and pastries tender and delicate. Protein varies from 7 to 9 percent.

Pastry flour is milled from soft wheat, generally from soft red winter wheat. It is low in protein—typically 7–9.5 percent—and is not usually bleached. Pastry flour is ideal for cookies and many pastries.
Soft wheat flour - has a lower gluten content

Wheat gluten protein

Wheat is one of the most important cereal crops worldwide, in terms of production and utilization. It is a major source of energy, protein, and dietary fibre in human nutrition and animal feeding. The ability of wheat flour to be processed into different foods is largely determined by the proteins.

Bread wheat (Triticum aestivum) produces one-seeded fruits, which are called grains or kernels. The pleasant flavor, long shelf-life and unique gluten forming characteristics of wheat products like pasta, noodles, bread, chapatti etc. make them very attractive among other cereals.

The wheat gluten proteins are known as the storage proteins that are found in the starchy endosperm of the grains. These proteins play a major role in the bread manufacture.

Wheat gluten is a protein that has unique properties. When hydrated and mixed, it forms a very extensible, elastic structure that is responsible for the gas-holding ability of bread dough.

Gluten comprises some 75% protein on a dry weight basis, with most of the remainder being starch and lipids. Their biological function is to provide carbon, nitrogen and energy sources for seed germination and seedling growth.

The two distinct groups of the gluten polymer that were classified reflected their solubility in 70% ethanol, namely glutenins and gliadins. The gliadins are single polypeptide chains and the glutenins are comprising polymers with subunits linked by disulphide bonds, is particularly important. Glutenins and gliadins are recognized as the major wheat storage proteins, constituting about 60-85% of the total grain proteins and they tend to be rich in asparagine, glutamine, arginine or proline but very low in nutritionally important amino acids lysine, tryptophan and methionine.

Wheat prolamins are the major storage proteins present in the starchy endosperm cells of the grain, where they are synthesized and deposited via the secretory system. Prolamins are high content of the amino acids, proline and glutamine.

The non-prolamin proteins; albumins and globulins of wheat, comprises 15-20% of total wheat flour proteins. Albumins are soluble in water and globulins are soluble in salts.

Recent discoveries found that wheat gluten can be processed into texturized vegetable protein for meat application. The popularity of texturized vegetable proteins that contain wheat proteins is rapidly increasing.
Wheat gluten protein

Nutrient in barley grain

Cultivated barley, Hordeum vulgare, is mainly grown for animal feed, for malting and brewing in the manufacture of beer and for distilling in whisky manufacture.

Studies have associated the regular consumption of barley with its potential to reduce the risk of certain diseases, such as chronic heart disease, colon cancer, high blood pressure and gallstones.

Whole grain barley has high levels of dietary fiber (14.8 g/100 g raw material) and good levels of other bioactive compounds, vitamin B and E and also minerals, such as iron (6 mg/100 g raw material), zinc (3.3 mg/100 g raw material), and calcium (50 mg/100 g raw material).

Due to its high viscosity in aqueous media, the soluble cell wall polysaccharide (1→3),(1→4)-β-glucan is an important nutritional component. β-glucan play a pivotal role as nutraceutical food in preventing cardiovascular diseases, controlling diabetes mellitus, regulating cholesterol level in body.

Barley is a good source of dietary phenolic compounds, which can be found free as well as bound to fiber. The flavanols, especially catechin, procyanidins and prodelphinidins, are the main compounds in the free phenolic fraction of barley grain.

Barley has a significantly higher protein content (10–20%) compared to corn (9.5%), rice bran (10–16%), and wheat (14%). The storage proteins in barley grains belong to two solubility classes, namely globulins (a fraction soluble in dilute salt solutions) and prolamins (a fraction soluble in aqueous alcohols).

Barley protein contains essential amino acids and is characterized by desirable functional properties (such as elasticity, water holding, and emulsifying capacity), which makes it an ideal component of food supplements.

Barley protein is rich in prolamin storage proteins (hordeins) and has moderate nutritional quality, being particularly deficient in lysine. These hordeins are not single proteins but complex polymorphic mixtures of polypeptides. β-hordein is the largest fraction accounting for between 70 and 90% of the total hordein content, and it is the major storage protein of the barley grain. β-hordein can be further broken down into subunits B1, B2 and B3 based on their electrophoretic capabilities.

The increase of protein content is accompanied by decreases in essential amino acids, mainly lysine. It was suggested that nutritional quality of the grain decreases with increasing grain protein contents as an increasing proportion of the nitrogen is incorporated into prolamin storage proteins.

The other barley proteins consist of a mix of albumins, globulins and glutelin. Globulins cover 10–20% of the total protein content of barley grains.
Nutrient in barley grain

Avenin in oats

Prolamins are known as gliadin in wheat, hordein in barley, secalin in rye and avenin in oats. Avenin in oats, which is a protein similar to gluten but safer for most people with celiac disease.

The avenin which makes up 10 - 15% of the total seed protein content of oats, in contrast to wheat, in which prolamins represent 80% of the total seed protein content.

Avenins, like the prolamins of other cereals, are highly polymorphic, both within and between genotypes.

The avenins in the genus Avena are free of the known celiac disease immunogenic epitopes from wheat, barley, and rye. The proline content in avenins is also less than that found in gliadins, secalins, and hordeins. Avenins are also more easily digested by gastrointestinal proteases, which is in contrast to gliadins, secalins, and hordeins.
Avenin in oats

Secalins in rye

The prolamin proteins in rye are termed secalin proteins (equivalent to wheat gliadins). The rate of accumulation of secalin in developing rye grain was at a maximum between 3 and 5 weeks after anthesis (the flowering period of a plant, from the opening of the flower bud).

The prolamin content in wheat, barley and rye constitute about 40% of the protein, whereas it comprises about 15% in oats.

Secalins are divided into four types: HMW (high molecular weight), γ -75, ω and γ -40 secalins. The monomeric γ-40 secalins account for about 24% of the total secalin fraction. While, monomeric ω-secalins account for about 17% of the total secalin fraction of rye. The other two:
*γ -75 secalins made up about 46% of the total secalins
*HMW secalins account for about 7% of the total secalins

Secalin is the major protein of the rye grain, but rye is not as suitable for bread making as wheat. Rye is not suitable for consumption by celiac patient. Celiac disease (CD) is a gluten-sensitive enteropathy that has a prevalence of 0.3–2.4% in most populations. The disease is triggered by ingestion of gluten, the proline-rich storage proteins of wheat, barley, and rye.
Secalins in rye

Five classes of common American wheat

Five principle classes of wheat are commonly grown in North America:
Hard Red Winter 
This wheat is grown in large quantities. It has moderately high protein content and used for bread. Hard Red Winter Wheat mostly grown in the central and southern Great plain.

Soft Red Winter Wheat 

Used for cakes and pastries. This wheat grows in the eastern and southeastern states of United States.

Hard Red Spring Wheat 
This wheat has the highest protein content of North American wheat and is used for manufacturing bread. It grows mainly in northern Great Plains.

White Wheat 
This wheat is suitable for pastry flour. It grows in New York, Michigan and the Pacific Coast states.

Durum wheat  
Grow in North Dakota and other northern Plains states.  This is the hardest of the five wheat classes. It is for spaghetti

Five classes of common American wheat

Amaranth grain

Amaranth a little known crop of the Americas, it’s grown either as a grain crop or as a leafy vegetable. Amaranth grain is very small (about half the size of millet), and may be light yellow, brown-yellow or brown-black in color.

Amaranth grain species are ‘pseudocereals’. Well-known Amaranth grain includes A. cruentus, A. hypochonriacus and A. caudatus.  This species is a crop in the Andean highlands of Argentina, Peru and Bolivia.

Amaranth grain makes a tasty porridge and can be toasted to make crunchy topping. The flour must be mixed with other flour for baking.

Amaranth grain has a high protein as well as a high-fat content and can supply an excellent balance of carbohydrates, fats and proteins. Amaranth has a protein content as high as 16%, which is somewhat higher than that found among commercial varieties of common cereals.

The grain is easy to digest and customarily given to those who are recovering from an illness or a fasting period.

Amaranth is high yield potential. It typically gives a grain yield of 2,250 – 4,500 kg/ha and fresh weight of leaf and stem of 30,000 – 60,000 kg/ha.
Amaranth grain

Oat and celiac disease

Celiac disease is an inherited trait: however its inheritance is complex and poorly understood.

The intestinal damage that occurs in celiac disease is associated with the abnormal immunological response and intolerance to certain protein fractions of cereals. Individual with celiac disease have a sensitivity to prolamin fractions of wheat (gliadin), rye (secalin) and barley (hordein).

The only treatment for celiac disease is a strict gluten free diet for life. Previously, oats were also included in the list of cereals causing symptoms in celiac patients.

Celiac disease is characterized by diarrhea, emaciation, aphthous stomatitis malabsorption.

Finnish celiac disease and dermatitis herpetiformis patients had been using oat-containing gluten-free diets since 1997 (Peraaho M. Oats can diversify a gluten-free diet in celiac disease and dermatitis herpetiformis. J Am Diet Assoc 104(7):1148-1150).

The researchers found that 1000 randomly selected members of the Celiac Society, 73% with celiac disease and 55% with dermatitis herpetiformis.

Since 1995, several additional studies published found no adverse effects associated with the regular consumption of moderate amounts of oats. These studies have shown that oats suitable for both adult and child patients.
Oats and celiac disease

Quality protein maize (QPM)

Maize is a major food for millions of the poor in Africa and Latin America. The protein in normal maize is however, of poor nutritional value due to the limited concentrations of two essential amino acids, lysine and tryptophan.

During the last few decades scientists have developed and improved quality protein maize which looks and tastes like normal maize and yields as much or more.

Quality protein maize contains opaque-2, a single-gene mutations that alters the protein composition of the endosperm portion of the kernel and nearly doubles lysine and tryptophan concentrations.

The name ‘opaque-2’ was coined for the gene because it gave the kernels a chalky appearance.

The nutritive value of QPM protein approaches that of protein from milk. The biological value of common maize protein is equal to about 40% that of milk protein, whereas the biological value of QPM protein is about 90% that of milk proteins.

QPM can help reduce protein deficiencies, particularly in young children, in settings where maize dominates diets.
Quality protein maize (QPM)

Gluten in wheat

Gluten is a storage protein found in several grains such as wheat, barley and rye.

Wheat gluten is the water insoluble complex protein fraction separated from wheat flours.

It is primarily a mixture of two types of protein from the wheat kernel glutenin and gliadin.

Gluten helps hold things together. It gives elasticity to dough and will help it rise and maintain its shape. It gives bread its structure and chewiness.

Wheat gluten is a protein-lipid-carbohydrate complex, formed when flour is hydrated: when the starch is washed away with more water, the gluten coheres as an elastic, insoluble, rubber like mass, which can be dried to give a cream colored powder.

Gliadin is the fragment of the gluten-chain that can’t be digested by those with celiac disease or non-celiac gluten-intolerance.

As a natural source of protein, gluten is commonly used as an additive on foodstuffs with a low protein value and it’s also used in a variety of hair and skin care product.
Gluten in wheat

Protein compositions in cereal grains

Since the beginning of agricultural production in the prehistoric time, cereals have been the main agricultural products in most parts of the world playing important role in nutrition generally, and in the protein supply. 

Cereals are quite similar in gross composition being low in protein and high in carbohydrate.

Protein composes 7-14% of the grain, depending on the grain. The nutritional quality of cereal proteins is not as high as that of most animal proteins. Cereals grains are also low in total protein compared to legumes and oil seeds.

Lysine is the first limiting essential amino acid for man, although rice, oats, and barley contain more lysine than other cereals. Corn proteins is also limiting in the essential amino acids tryptophan, while other cereals are often limiting in threonine.

The protein is low of biological value and therefore, less efficient in supporting body needs. Combining food sources of protein is common in cultures throughout the world.

Cereals together with oil seeds and legumes, supply a majority of the dietary proteins to the bulk of populations in developing nations.

Of all the cereal grains, oats ranks highest in protein and runs neck to neck with wheat as the all-round most nutritive cereal grain.
Protein compositions in cereal grains

Protein in wheat

Wheat is supreme among cereals largely because its grain contains proteins with unique chemical and physical properties.

Wheat has achieved its position as a basic food crop as a result of a number of attributes, not the least of which is the unique capacity of its protein to from an elastic, cohesive mass when mixed with water.

Wheat kernel consist of three main parts; bran, germ and endosperm. The endosperm is the white, starchy part of the kernel that remains when the bran and germ are removed.

Depending on its source, the wheat endosperm contains about 68 to 76% starch and 6 to 18% protein. In white flour proteins act as binding agents that hold the starch granulates together in the endosperm.

About 80% of the protein the protein in flour are called glutenin and gliadin. These two protein, when combined with water and mixed in a dough, form an elastic substance called gluten.

Gluten exhibits plasticity, strength, and elasticity, which means that it is capable of deformation when placed under pressure, that it tends to resists that deformation and that it tends to reassume its original form when pressure is released.

Other proteins present in white flour are enzymes, most importantly amylase also called diastase. This enzyme breakdown starch into simple sugars, which important for yeast fermentation.

Wheat protein are classified according to their extractability and solubility in various solvents:
*Albumin – soluble in water
*Globulin – insoluble in pure water but soluble in dilute NaCl solution and insoluble at high NaCl concentration
*Gliadin – soluble in 70% ethyl alcohol
*Gutenin – soluble in dilute acid or sodium hydroxide solutions.

Celiac disease is an immune disorder in which the body creates antibodies to gluten, a protein found in wheat and other grains. The resulting inflammation damages the surface of the intestinal wall, eventually causing the villi (fingerlike projections important for absorption) to become ‘flattened in appearance.

Protein levels in wheat are an important factors in determining hard red spring wheat prices and particularly for hard red spring grown in Minnesota, Montana, North Dakota and South Dakota. High protein commands higher prices in the market.  
Protein in wheat

Breakfast Cereals as a Source of Protein

Breakfast Cereals as a Source of Protein
The protein content of cereal grains is small relative to their carbohydrate content. For example, white wheat contains 75.4% carbohydrate but only 9.4% protein. For wheat made into flour, the ratio is even more in favor of carbohydrate.

With breakfast cereal, the situation is exacerbated when sugar is added to the formula. Because of then high ratio carbohydrate to protein, the protein content is frequently discounted.

The protein of breakfast cereal is often given short shrift because the protein in cereal grains is known to be deficient in certain essential amino acids, such as lysine. However, the combination of cereals with milk helps to alleviate this deficiency in many cases.

Although the protein quality of breakfast cereals as individual foods does not compare favorably with that of animal products like meat and milk, this is not to say that cereal grain proteins in general are devoid of specific amino acids as gelatin is devoid tryptophan.

Mixtures of cereal grains eaten in large enough quantities will supply all the essential amino acids needed for growth and maintenance, the cereal grains certainly make their contribution to human protein needs, as attested to by the millions of people throughout several millennia who survived primarily on such grain.

Their diets were sometimes supplemented with legumes and only occasionally with sources of animal protein, from meat, fish and milk. It is reasonable to assume that breakfast cereals can make the same contributions as the cereal grains did, provided the protein is not significantly diminished or damaging by processing.
Breakfast Cereals as a Source of Protein