Endosperm Composition: Nutrients and Structure

Whole grain kernels are made up of three components: the bran, germ, and endosperm, each of which contains beneficial nutrients.

The endosperm consists of two distinct cell types: aleurone cells, forming the outermost layer with thick walls, and central starchy endosperm cells that are rich in starch and gluten proteins.

The aleurone layer, a single layer of living cells, acts as a barrier between the starchy endosperm and the germ and is abundant in essential nutrients such as minerals, vitamin B, and protein.

The starchy endosperm is the main and largest part of the grain, serving as a storage compartment to provide energy for the germinating plant. Within the endosperm cells, proteins and starch are stored, resulting in a unique and highly dense structure.

The composition of wheat endosperm varies depending on its source, typically containing around 68 to 76% starch and 6 to 18% protein. It holds the highest proportion of protein, carbohydrates, iron, and B-vitamins like riboflavin and niacin, making it a valuable source of nutrients and soluble fiber.

Constituting approximately 83% of the kernel weight, the endosperm is the primary source of white endosperm flour. In white flour, proteins play a crucial role as binding agents, ensuring the cohesion of starch granules within the endosperm.
Endosperm Composition: Nutrients and Structure

Wheat kernel

Wheat is the primary grain used in U.S. grain products — approximately three-quarters of all U.S. grain products are made from wheat flour. The kernel or wheat berry, is the seed from which the wheat plant grows. The kernel’s size generally ranges from 5 to 9 mm long and weighs between 35 to 50 mg.

Wheat kernels are loaded with nutrients because they are whole grains. A cup of cooked berries has about 300 calories and is packed with vitamins, fiber, protein, and iron.

Each tiny seed contains three distinct parts that are separated during the milling process to produce flour —the endosperm, bran and germ

Bran
The bran is the multi-layered outer skin of the edible kernel and makes up around 14.5 percent of its weight. The bran contains a small amount of protein, trace minerals, and dietary fiber – primarily insoluble. The bran is an excellent source of insoluble fiber, which makes its inclusion in whole wheat flour valuable to improving digestive health for the end consumer.

Endosperm
Endosperm is about 83% of the kernel weight and the source of white endosperm flour. It has a high portion of protein, along with carbohydrates and iron. The endosperm is also a source of soluble fiber.

Germ
The germ is the embryo which has the potential to sprout into a new plant. It is the center of the kernel and only 2.5 percent of its weight. The germ contains minimal quantities of high-quality protein and a greater share of B-complex vitamins and trace minerals. Germ is often separated from flour during milling because the germ’s high fat content can limit the shelf life of flour.
Wheat kernel

Production of cornstarch

In producing cornstarch, the corn is inspected and cleaned, then place in vats, where it is steeped in warm water containing a small concentration of sulfur dioxide for about 40 hr, to begin breaking the starch and protein bonds.

The kernel swells to more than double the size and increases its moisture content from about 15% to 45%. The softened kernels are next run through an attrition mill to break up the kernels.

If not previously degerminated the steeped kernels are passed through mills that separate the germ and loosen the hull. The germ is removed by density separation in a cyclone.

The mass is then passed through tanks of water where the germs (being lighter) float and are skimmed off. The remaining endosperm, containing starch, corn gluten and hulls is then finely ground in steel mills.

The finely ground material is then passed through sifters to remove hulls, the starch and gluten passing through. The starch is separate from gluten by centrifugation. The starch-gluten suspension is concentrated by centrifugation and the higher and lower densities of gluten and starch facilitate centrifugal separation, again in a cyclone.

The gluten is dried and the starch is washed and dewatered. With hydrocyclones and a centrifuge the starch settles and separates from the water and fibers.

The starch fraction is finally dried to yield the familiar cornstarch. Cornstarch can be used as such in manufacture foods or be further converted into corn syrup by the hydrolytic action of acid or starch-splitting enzymes.
Production of cornstarch