Distribution of nutrients in the grain

To understand how processing affects the nutritional value of grains, an understanding of where nutrients are located in the grain kernel is required. Although there are slight differences between grains, the distribution of nutrients in the grain kernel is essentially the same for all grains.

Structure and Composition of the wheat grain

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

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

The ENDOSPERM contains:

• Mainly starch
• Most of the grain's protein (70-75%), including the gluten complex
• Little fat, except for oats which contain 5-9% fat, of which 80% is found in the endosperm
• Glucofructan, in wheat, which is similar in structure to inulin
• 32% of the grain's riboflavin content and 43% of the grain's pantothenic acid content
• Small amounts of thiamin, niacin and vitamin B6.

The ALEURONE layers contain:

• High quality protein (19% of grain's content) - it has a higher lysine content than the protein in the endosperm
• No starch
• High content of vitamins and minerals* (more than 70% of the grain's vitamin B6 and niacin content, 50-80% of its minerals, 50% pantothenic acid, 42% riboflavin and 33% thiamin).

The GERM contains:

• About 30% fat, but this varies widely - two thirds of the fat is unsaturated
• In maize, the germ accounts for about 12% of the total grain, compared to 2-3% fat for wheat and barley
• High quality protein (8% of grain's content)
• Vitamins, including vitamin E and most of the grain's thiamin content (64%). Also has riboflavin (26%), vitamin B6 (21%) and small amounts of pantothenic acid and niacin
• Minerals* and trace elements
• Small amounts of sugars, including sucrose, raffinose, stachyose.

The BRAN layers are high in dietary fibre and contain 2% lignin.

*Minerals found in grains include potassium, phosphorus (as phytic acid), magnesium, iron, zinc, calcium, sodium and manganese.

Phytochemicals, including lignans, phenolic acids and phytic acid are concentrated in the outer layers of the grain (aleurone and bran layers and the germ).