India produced 72.8 million tonnes of wheat during 2003. Wheat belongs to the genus triticum and there are 30,000 species.
The wheat produced in the country belongs to triticum aestivem (95 per cent), triticum durum (4 per cent) and triticum dicoccum (1 per cent) species which are used for bakery, pasta and traditional products.
The kernel of wheat is usually 1/8 – 1/4 inch long. In some kinds of wheat the tip of each kernel is covered by stiff hairs called the brush.
Wheat grains are ovoid in shape, rounded in both ends. Along one side of the grain there is a crease, a folding of the aleurone and all covering layers.
Distribution of carbohydrate in wheat fraction is given in.
|Percentage distribution of carbohydrate in wheat|
Its content depends on the variety grown, climate and soil conditions. Proportion of different proteins in wheat grain as percentage of total protein are:
Albumin – 5-10
Globulin – 5-10
Prolamine – 40-50
Glutelin – 40-50
Wheat proteins are rich in glutamic acid and low in tryptophan. Glutamic acid and aspartic acid are present in the amide form as glutamine and asparagine.
The high concentration of amide is important in determining the characteristic of the gluten. The bran and germ proteins have a higher content of essential amino acids than the inner endosperm proteins.
Thus, the biological value of endosperm proteins is much less than that of the whole wheat protein.
Acarbose, an oligosaccharide present in wheat is a competitive inhibitor of sucrase and pancreatic amylase. It lowers the postprandial blood glucose rise.
Milling of wheat:
Wheat is consumed mostly in the form of flour obtained by milling the grain while a small quantity is converted into breakfast foods such as wheat flakes and puffed wheat.
Indian wheat’s are hard and the moisture content is usually 8-10 per cent.
|Percentage composition of nutrients in different parts of wheat kernel|
Various steps are involved in making the flour. Figure 2-c gives the different steps. The traditional procedure for milling wheat in India has been stone grinding to obtain whole wheat flour.
In modern milling, the wheat is subjected to cleaning to remove various types of impurities together with damaged kernels.
This removes bits of straw and other coarse materials and second screen removes foreign materials like seeds.
It lifts off lighter impurities in the wheat. The stream of grain is directed across screens while air sucks off the dust and lighter particles.
After the aspirator it moves into a disc separator consisting of discs revolving on a horizontal axis.
The surface of the discs indented to catch individual grains of wheat but reject larger or smaller material.
The wheat then moves into the scourer, a machine in which beaters attached to a central shaft throw the wheat violently against the surrounding drum, buffing each kernel and breaking off the kernel hairs.
The stream of wheat next passes over a magnetic separator that pulls out iron and steel particles contaminated during harvesting.
High-speed rotators spin the wheat in the water bath. Excess water is thrown out by centrifugal force. Stones drop to the bottom and are removed. Lighter material float off leaving only the clean wheat.
Wheat is tempered, before the start of grinding, the process in which moisture is added. Tempering aids in separation of the bran from the endosperm and helps to provide constant controlled amount of moisture and temperature throughout milling.
The percentage of moisture, length of soaking, time and temperature are three important factors in tempering with different requirement in soft, medium and hard wheat.
Dampened wheat is held in a bin for 8-24 hours. The outer layers of wheat tend to be brittle and tempering toughens the bran coat to permit more complete separation of endosperm.
Within the kernel tempering also mellows or conditions the endosperm so that floury particles break more freely in milling.
Discs revolving at high speed in the scourer aspirator hurl the wheat against finger like pins. The impact cracks down any unsound kernel which are rejected.
The “first break” rolls of a mill and are corrugated rather than smooth, break into coarse particles.
The broken particles of wheat and bran go into a box like sifter where they are shaken through a series of cloth or screens to separate larger from the smaller particles.
Larger particles are shaken off from the top by leaving the final flour to shift towards the bottom.
The top fractions and particles of endosperm graded by size are carried to separate purifiers. In a purifier a controlled flow of air lifts off bran particles while cloth or screen separate and grade coarse fractions by size and qualities.
The down purifier:
Four or five additional break rolls with successively final corrugations and each followed by a sifter are usually used to rework the coarse stock from the sifter and reduce the wheat particles granular middling’s as free from bran as possible.
Germ particles being somewhat plastic will be flattened by a later passage through the smooth reduction rolls and tend to be easily separated.
The process is repeated over and over again. Sifters, purifiers reducing rolls until the maximum amount of flour are separated consisting of at least 72 per cent of wheat.