Skip to main content

Strucuture of a Wheat Kernel and its Chemical Composition

Wheat Kernel

Picture above give an idea of the structure of a wheat kernel and its various constituents, as well as its % mineral matter (ash content on dry matter basis). The amount of each constituent in the whole kernel is also given in percent.
Chemical composition of different parts of the grain (According to Bruckner)

The flour cells (endosperm) are mainly filled with starch and protein, and represent a dry reserve for the germ. The sprouting germ derives its first nourishment from this part. The thickness of the whole bran varies with the varying thickness (0.048 – 0.066 mm) of the longitudinal cells (pericarp). The colorless aleurone cells do not cover the germ. The ash content of these cells is more than 20 times higher than that of the white flour (endosperm). This layer is approx. 0.05 mm. thick and contains up to 30% protein (but no gluten protein), lipids (another 30%), vitamins and enzymes. A toxic substance has been found in the aleurone fat of the rye kernel which is of importance in animal feeding.

The nuccelar epidermis is situated between the aleurone cells and the seed coad (testa). The latter is only semi-permeable for moisture, besides the carrier of the brown color, and prevents the penetration of mold (fungi) into the kernel. In older publications, the hyaline layer was held responsible for the semi-permeability.

The greatest part of the vitamin B1 content of the whole kernel is concentrated in the scutellum, i.e. 62%, whereas another 32% is contained in the aleurone cells. A point to be considered is that this 62% is concentrated in the scutellum in only 1.5% of the kernel weight. The whole endosperm only contains 2.8% of the total vitamin B1 content, and the germ itself only 2%.

The actual germ takes up water very easily and swells to a great extent. It is high in protein, fat and mineral matter, and is also rich in enzymes and vitamins. Undamaged, it does not spoil. The scutellar ephitelium cells adjacent to the endosperm grow to approximately double their length into the flour during germination of the kernel.



Popular posts from this blog

WHAT THE TESTS MEAN

WHEAT GRADE TESTS Wheat grades reflect the physical quality and condition of a sample and thus may indicate the general suitability for milling. The U.S. grade for a sample is determined by measurement of such factors as test weight, damaged kernels, foreign material, shrunken and broken kernels and wheat of contrasting classes. All numeric factors other than test weight are reported as a percentage by weight of the sample. Grade determining factors include: TEST WEIGHT is a measure of the density of the sample and may be an indicator of milling yield and the general condition of the sample, as problems during growing season or at harvest often reduce test weight.DAMAGED KERNELS are kernels which may be undesirable for milling because of disease, insect activity, frost or sprout damage, etc.FOREIGN MATERIAL is any material other than wheat that remains after dockage is removed. Because foreign material may not be removed by normal cleaning equipment, it may have an adverse effect on m…

Product Tests (A Guide to Understanding Wheat and Flour Quality)

A.Pan Bread

Formula :
Procedure 1. Flour and other ingredients are mixed with a yeast suspension to form a dough. 2. The dough is mixed until it reaches optimum dough development. 3. The dough is rounded and placed into a fermentation cabinet at 30 degrees Celsius and 85 percent relative humidity for 105 minutes. 4. First Punch – The dough is passed through a sheeter, folded twice, and returned to the fermentation cabinet for 50 minutes. 5. Second Punch – The dough is passed through a sheeter, folded twice, and returned to the fermentation cabinet for 25 minutes. 6. The dough is molded into a cylinder shape and proofed in a pan for 62 minutes. 7. The dough is baked in a 215 degrees Celsius oven for 24 minutes and then cooled to room temperature.
Results 1. Pan bread is evaluated for processing characteristics, external and internal characteristics, and texture. The results are expressed as a numerical score based on comparison to a control sample. 2. Pan bread dough is evaluated during …

Dough and Gluten Strength Tests

1.Glutomatic Wet gluten content is determined by washing the flour or ground wheat sample with a salt solution to remove the starch and other solubles from the sample. The residue remaining after washing is the wet gluten. During centrifugation, the gluten is forced through a sieve. The percentage of gluten remaining on the sieve is defined as the Gluten Index, which is an indication of gluten strength. A high gluten index indicates strong gluten. Wet gluten content results are expressed as a percentage on a 14% moisture basis; for example, 35% for high protein, strong gluten wheat or 23% for low protein, weak gluten wheat.
The wet gluten test provides information on the quantity and estimates the quality of gluten in wheat or flour samples. Gluten is responsible for the elasticity and extensibility characteristics of flour dough. Wet gluten reflects protein content and is a common flour specification required by end-users in the food industry.
2.Farinograph The farinograph determines …