Horny endosperm

Endosperm constitutes the main part of the corn kernel and consists of 85 to 90% starch, 8 to 10% protein, and a small amount of oil and other compounds. Corn endosperm can be divided into two distinct parts floury and horny endosperm. In floury endosperm, starch particles are round and are dispersed loosely in the protein matrix. In the horny endosperm, the protein matrix is stronger and starch particles are held more firmly. Starch granules are encased in the continuous protein matrix. The tighter setting in horny endosperm gives starch particles a polygonal shape. On average, the amount of horny endosperm in the corn kernel is twice that of the floury endosperm. However, this ratio is a function of the corn kernel protein content (Wolf et al., 1952). 

The second stage of steeping is the sulfur dioxide diffusion stage in which sulfur dioxide diffuses with the water into the corn kernel through the base end of the tip cap and moves through the cross and tube cells of the pericarp to the kernel crown and then slowly into the horny endosperm. The second stage is diffusion limited because of the specific path required for water going into the kernel. 

Figure 9.2 Section of steeped corn horny endosperm (1 Op,m thick, iodine stained, magnified X612 SG, starch granules PM, protein matrix CW, cell wall).

Wu YV, Strongfellow AC 1981. Protein concentrate from air classification of flour and horny endosperm from high-lysine sorghum. J Food Sci 46 304-305. 

When the embryo and endosperm are being formed, the ovule enlarges and its integuments become modified to form a hard horny seed coat which encloses the endosperm surrounding the embryo. The ovary, containing the ovules, has by this time ripened to form a three-valved loculicidal capsule enclosing the seeds. 

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