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.