Wheat flour: Applications in the baking industry

Wheat (Triticum spp.) is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. It is a noble cereal of high global consumption, is produced in quantity and quality by a few countries and imported by developing countries, which in most cases do not have enough production to supply the internal market. Other cereal grains include corn (maize), oats, rice, and rye.

Wheat grain is a staple food used to make flour for leavened, flat and steamed breads, biscuits, cookies, cakes, breakfast cereal, pasta, noodles, couscous and for fermentation to make beer, other alcoholic beverages. Wheat is more popular than any other cereal grain for use in baked goods. Its popularity stems from the gluten that forms when flour is mixed with water.

Wheat varieties are called:
· "Clean," "white," or "brown" if they have high gluten content
· "Soft" or "weak" flour if gluten content is low.
· "Hard" flour, or bread flour, is high in gluten, with 12% to 14% gluten content, and has elastic toughness that holds its shape well once baked.

Wheat flour is the finely ground product obtained in the milling of wheat, and consists essentially of the starch and gluten endosperm. Whole wheat flour contains all three parts of the kernel, white flour is milled from the endosperm. Whole wheat flour is considered a whole grain product because it contains the entire wheat kernel.

When flour is mixed with water, glutenin and gliadin form strands of gluten, important in the structure of baked goods. In fact, wheat is the only common cereal grain that contains sufficient glutenin and gliadin for the formation of good-quality gluten for bread making.

Wheat flour quality is directly related to the wheat gluten and with the use of appropriate application of mechanical work to form a viscoelastic network, the structure is the basis for bakery products and pasta.

Wheat is also preferred because of its mild, nutty flavor. Wheat flour is unique among cereals due to its ability to form a three-dimensional structure when mixed with water.

Wheat germ is high in protein, fat, B vitamins, vitamin E, and minerals. These nutrients are important to the germ as it sprouts. While germ protein does not form gluten, from a nutritional standpoint it is of a high quality.
Wheat flour: Applications in the baking industry

Wheat prolamins

Mature cereal grains contain about 8-15% protein. Prolamins, the major class of storage proteins in cereals are synthesized at the endoplasmic reticulum during seed development and deposited into subcellular structures of the immature endosperm, the protein bodies.

Prolamins are defined as proteins extractable in aqueous ethanol. Prolamins of wheat are the major components of gluten, the properties of which determine the quality of wheat flour for various technological processes including breadmaking.

Wheat prolamins consist of a mixture of monomeric gliadins and polymeric glutenin subunits, which are present in approximately equal amounts. Together they form 80% of the total storage protein content in the wheat kernel. The remainder is albumins (12%) and globulins.

The glutenins are composed of a group of high molecular weight subunits, as well as a group of low molecular weight subunits. the low molecular weight glutenins are structurally similar to the S-rich gliadins and are therefore termed as aggregated gliadins. The monomeric gliadin subunits range in size from about 30 to 60 kDa and were originally classified into groups of α, β, γ and ω gliadins, based on their migration in acidic gels.

The prolamin fractions of wheat and related grains are implicated in the causation of celiac disease. The prolamins are the major storage proteins in these grains, so all of these grains contain ample gluten and are considered hazardous for celiac sufferers.
Wheat prolamins

What is gliadin?

Seed storage proteins (about 85% of endosperm proteins) are traditionally classified into monomeric (gliadins) and polymeric (glutenins) proteins, based on their solubility.

On the basis of electrophoretic mobility at low pH the wheat gliadins may be separated into the slowest group named the ω-gliadins and three faster groups, named the α, β and γ-gliadins.

The amino acids sequences of some gliadins are known. A very common N-terminal sequence found in α, β and γ-gliadins is Val-Arg-Val-Pro-Glu-Leu-Glu-Pro.

Due to the differences in cysteine content the gliadin components may be divided into S-rich (α, β and γ-gliadins) and S-poor (ω-gliadins) components.

All gliadin components have extremely high glutamic acid content. In some ω-gliadins the glutamic acid content is higher than 50%.

Although not major participants in the gluten polymer, the monomeric gliadins contribute to dough physical/chemical properties by extensive hydrogen bonding with the gluten polymer.

Gliadins are rather hydrophobic, hence their solubility in water or salt solution. More hydrophobic gliadins (the γ-gliadins) increase bread loaf volume, while gliadins from more hydrophilic end of the spectrum decrease loaf volume.
What is gliadin?

Defects and impurities of wheat

During harvesting and postharvest handling and storage of wheat at the farm, it becomes exposed to a wide range of foreign matter comprised of various types of seeds such as oats, barley, wild oats, corn, pea, flax, rapeseed, mustard, wild buckwheat and such.

In remote areas certain countries high levels of impurities such as sand or dust result from manual harvesting,

Quality attribute are measured using a multitude of specific tests designed or provide information on the various characteristics of grain.

These include the measurement for conditions such as kernel density; moisture; damage, broken or split kernels; impurities and other visual defects.

Wheat and other cereal grains are subject to government inspection and grading. In establishing the grain grades for wheat, certain defects and impurities in wheat have been identified as definitely affecting the yield and quality of the wheat.

With a proper grading system in place, as in major grain-exporting countries, tolerance level for all the factors listed as part of the grading factors is established. The grade-determining factors should be those that relate to sanitary quality purity, and soundness (absence of imperfections).

Consequently, it is important to consider some of the causes of these defects and their effect on the quality of wheat.
Defects and impurities of wheat

Wheat intolerance

Sufferers from wheat intolerance are sensitive to the whole grain of wheat, whereas people with celiac disease are sensitive to the wheat protein, gluten.

It is a condition in which the body does not adequately digest wheat, although the reaction remains a metabolic disordered and does not involve the immune system.

Wheat intolerance is much more common than wheat allergies and those who have it usually have a delayed onset of symptoms as long as two to three days later.

These people suffer with various degrees of symptoms, ranging from stomach discomfort to chronic headaches and diarrhea. Wheat intolerance also gives symptoms of asthma, eczema, general aches and pains, mood swing and itchy skin.

Some individuals with wheat intolerance may still be able to eat wheat occasionally or in small servings.
Wheat intolerance

Wheat product: bagel

Bagels are a doughnut-shaped yeast roll with a dense, chewy texture and shiny crust. It is also fine grained.

The long standing myth is the bagel was created by a local baker to celebrate the victory of Poland’s King Jan III Sobiesky over the Ottoman Turks in 1683, and was given the trade name of buegel.

The bagels are boiled in water before they are baked. It will them characteristics firm, chewy interior. Industrial bagels may not be boiled and may have a soft crumb.

The hole made the bagel easy to transport, slipping it on a rod or a rope – the way that it was thought to be originally carried. Although plain bagels are popular, many bagel bakeries make plain, poppy seed, sesame seed, garlic, onion, cinnamon raisin, egg, salt, everything bagels and so on.

The traditional way to enjoy a bagel is with lox or smoked salmon and cream cheese.

Bagels came to America in the late 19th century along with Eastern European immigrants. The bagel was modified in America to its present form, which is generally thicker than its European antecedents.
Wheat product: bagel

Durum Wheats

Compared to bread wheat, Triticum durum, is far less grown and it has a lower resistant to cold, long winter but is better adapted to drought conditions.

The beginning of the durum wheat industry in United States was made in 1898, when Mark Alfred Carleton, Cerealist of the department went to Russia in search of drought resistant cereals for the dry lands.

Durum wheat production is concentrated in North Dakota, with smaller amounts in Montana and South Dakota and still smaller amounts in Arizona and California.

It is riskier to grow than non-durum wheats and durum wheat traditionally has commanded a higher price. 

Durum wheat cannot be used to produce flour for bread making; rather it is milled to supply semolina for making macaroni, spaghetti, noodles, etc.

Protein content and gluten composition are generally considered to be main factors affecting dough properties and cooking quality of durum wheat pasta.

Durum wheat is divided into three subclasses,:
*Hard amber durum wheat, which has 75% or more of hard, vitreous kernels of amber color
*Amber durum wheat, which has 60 - 75% of hard, vitreous kernels of amber color
*Durum wheat, which has less than 60% of hard, vitreous kernels of amber color
 Durum Wheats

Hard Red Spring Wheat

Three market classes of wheat are typically grown: hard red winter wheat, hard red spring wheat and durum wheat.

Hard red spring wheat is grown principally in North and South Dakota, Montana, Minnesota and the Prairie Provinces of Canada, where the winters are too severe to grow winter wheat.

It may be grown in other areas to replace winter wheat that has failed due to winter killing, drought or other causes.

The principle hard red spring wheat districts have a fairly deep black soil and dry, hot summers, both important factors in the production of a high grade wheat suitable for milling as bread flour.

Hard red spring wheat is divided into three subclasses according to its content of dark, hard, and vitreous kernels. These subclasses are:
*Dark northern spring wheat – hard red spring wheat with 745% or more of dark, hard and vitreous kernels
*Northern spring wheat- hard red spring wheat with 25% or more but less 75% dark, hard and vitreous kernels
*Red spring wheat – hard red spring wheat with less 25% of dark, hard and vitreous kernels.

Overall, hard red spring accounts for about 20% of the total wheat acreage in the United States.

This class of wheat is typically used for making pan, hearth bread and rolls. The highest quality breads are made from hard red spring wheat. This due to it has highest amount of gluten of the commonly grown wheats.
Hard Red Spring Wheat

Gliadin protein in wheat flour

Gliadin is a heterogeneous group of prolamines. They are rather hydrophobic, hence their insolubility in water or salt solutions. They are single chain proteins and such disulfide bonds that occur are all intra-molecular. 

Gliadin is the major storage protein in wheat. Wheat flour has a total protein content of about 10% and approximately 10% of these proteins are made up of alcohol soluble gliadin proteins.

Gliadin is practically as abundant in the wheat kernel. The proportion of gliadin in wheat flour has much to do with its quality for bread making purpose. It is said that gliadin gives tenacity and elasticity to the gluten, while glutenin gives strength; but the two proteins must be present in proper protein of the gluten is to have the properties desired in bread-making.

In order to make a large light loaf of bread, the flour should have a fairly high gluten content and its gluten should contain a high proportion of gliadin.
Gliadin protein in wheat flour

Wheat kernel

Kernel is the seed from which the wheat plant grows., Each tiny seed contain three distinct parts that are separated during the milling process. Kernel sometimes called the wheat berry.

In botanical terms, the wheat kernel, like that of other cereal grains, is a caryopsis or single seeded, indehiscent dry fruit. Caryopsis, is ovoid in shape with a longitudinal crease.

The length of the kernel varies with the type of wheat and conditions of growth, but is generally about 4-8 mm, The outer layer or epidermis is a sheath for other layers of cells, which constitutes a pericarp about 50 um thick.

During growth the lateral potion of the seed fold inward and the seed elongates, forming a fold or groove upon its upper surface.

Wheat kernels are the part of the plant that is milled into flour. The wheat kernel as whole grain has four main parts: the germ, the endosperm, the bran and the husk.

Endosperm makes up the bulk of the wheat kernel, over 80 percent of it. It is the whitest part, partly because it contains mostly starch.

The bran acts a s barriers to protect the grain and makes up over 8% of the weight of the kernel.

The germ is the part that grows into a wheat plant and therefore contains concentrated food to support the new life - it is especially rich in vitamins and minerals. Wheat germ represent only 2-3% by weight of the kernel and it is available as a separate entity because it is an important source of vitamin E.
Wheat kernel

Lipid in Wheat Flour

Wheat flour contains 1.4-2.0% lipids, depending on milling extraction rate. Most it is contributed by endosperm.

The lipids divided into free (0.8-1.0%) and bound (0.6-1.0%) forms. They further divided into non-polar (50.9%) and polar (49.1%).

Polar lipids composed of triglycerides, diglyceride, monoglycerides, free fatty acids and sterol. The major portion of non-polar mainly lipids, phospholipids, and galactosyl glycerides.

Mono and diglycerides have weak polar head groups, their polarity also depends on the size of fatty acids chain present. Free fatty acids which composed 20% of non-starch non-polar lipids are the least non-polar in the non-polar faction.

Linoleic acid is the major unsaturated free-fatty acids and palmitic acid is the major saturated free fatty acids.

The bound lipids exist as starch inclusion complexes. The nonstarch lipids, about 85% of the total, participate in the chemical, physical and biochemical processes important for the preparation of baked goods.

Flour lipids play an important role in the dough-mixing and baking processes. They interact and form complexes with gluten protein and contribute to the stabilization of gas-cell structure, thus having significant effects on loaf and on final texture.

Some oxidation of lipids by wheat lipoxygenase occurs in dough, but more important oxidations resulting in dough improvement require soya lipoxygenase, and both contribute to the oxygen requirement of the dough.

Lipids have a positive effect on dough formation and bread volume, namely polar lipids or the free fatty acid component of the nonstarch lipids, whereas non-polar lipids have been found to have a detrimental effect on bread volume.
Lipid in Wheat Flour

Wheat Structure

Wheat Structure
Wheat structure is a single seeded fruit, 4 to 10 mm long, consisting of a germ and endosperm enclosed by an epidermis and a seed coat.

The fruit coat or pericaprs (45 to 50 um thick) surrounds the seed and adhere closely to the seed coat.

The wheat color, depending on the species and other factors is red a to white and is due to material present in the seed coat.

Wheat also is classified based on physical characterizes such as red, white soft, hard spring or winter.

The outer pericaprs is consist of the epidermis and hypodermis. The epidermis consists of a single layer of cells that from the outer surface of the kernel.

On the outer walls of the epidermal cells is the water impervious cuticle. Some epidermal cells at the apex of the kernel are modified to form hairs.

The hypodermis is composed of one to two layers of cells. The inner pericaprs is composed of intermediate cells and cross –cells inward from hypodermis.

Long and cylindrical tube cells constitute the inner epidermis of the pericaprs. In the crease, the seed coat joins the pigment strand, and together they form a complete coat about the endosperm and germ.

Three layers can be distinguished in the seed coat: a thick outer cuticle, a “color layer” that contains pigment, and a very thin inner cuticle.

The bran comprises all outer structures of the kernel inward to, and including the aleurone layer.

This layer is the outer layer of the endosperm, but is considered as part of the bran by millers.

The aleurone layer is usually one cell thick and almost completely surrounds the kernel over the starchy endosperm and germ.

The endosperm is composed of peripheral, prismatic and central cells that are different in shape, size and position within the kernel.

The endosperm cells are packed with starch granules, which lie embedded in a matrix that is largely protein.
Wheat Structure