THE KERNEL

A Well-Organized Reserve of Nutrients

The main components of cereal grains are the hull, pericarp, testa, aleuron, endosperm and the germ. Rye is, in contrast to wheat, a special grain because it is mostly consumed as whole grain flour in breads and other cereal products. The grains may also be fractionated into different types of flour during the milling process.

Microscopic picture of Rye Kernel


Before rye grains can be used in food production, the outer part of the grain, the hull, must be removed. After hulling, which generally occurs during threshing, the grains are used as whole, cracked or flaked, or they are ground to make flakes or flour. The starchy endosperm constitutes about 80-85% of the weight of the whole kernel, the germ 2-3% and the outer layers about 10-15%.

In the milling process the kernel can be ground and fractionated into different types of flour and bran. Ash content is a concept used to indicate the amount of inorganic minerals in food samples. Because the majority of minerals are located in the outer layers of the kernel, the ash content of flour indicates, how much of the outer layers have been included in the flour. In white wheat flour (ash content 0.7% or less), about 30% of the outer layers of the kernel have been removed. Traditional Nordic rye bread and crisp bread are made of whole grain rye flour (ash content about 2%), where all of the components of the kernel are present.

Cereals are the most important source of dietary fibre in many countries. The fibre in cereals is located mainly in the outer layers of the kernel, especially in the bran. Wheat and rye have similar bran content, but rye contains more cell walls within the endosperm, and thus has a higher fibre content (Hansen et al. 2003). Rye is also an exceptionally good source of dietary fibre because it is very often consumed as whole grain products.

The Kernel and Different Flour Fractions Derived from it



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