Principles of grains processing systems

Grain processing systems are generally based on the separation of the following components of the grain:

• Bran is the hard, brownish outer protective skin of the grain (varies from 6% in corn to 16% in wheat). Bran layers include the cuticle, mesocarp, cross layer, tube cells and testa. The bran layers are a concentrated source of dietary fibre.
• Endosperm is the inner part of the grain (varies from 60% in rice, barley and oats to 80% of the grain in wheat). It provides the growing plant with food. The main nutrients in the endosperm are protein and carbohydrate.
• Aleurone consists of one or more layers of cells between the bran and the endosperm (8-10% of total grain). The number of layers vary from 1 cell thick in wheat, rye, oats and maize to up to 3 cells thick in barley and rice. The aleurone layer is a concentrated source of vitamins, minerals and other nutrients.
• Germ is the part of the seed that becomes a new plant if the seed is sown (varies from 12% in maize and 10% in sorghum to as low as 2% or 3% in other grains). It consists of the embryo and the scutellum. Most of the grain kernel's fat and vitamin E content is found in the germ.

Structure and Componsition of the wheat grain

Schematic Diagram of a longitudinal section of wheat grain through crease and germ

Source: Mugford, D.C. et al. (1979).