Source: Ref. 32

the outer bran (pericarp, seed coats, and nucellus) is high in cellulose, hemicelluloses, and minerals. The germ is high in proteins, lipids, sugars, and minerals; the endosperm consists largely of starch granules embedded in a protein matrix. The structure of rice, barley, oats, rye, and triticale are similar in structure to wheat, except that rice has no crease.

Rice. Rice is a covered cereal. In the threshed grain (termed rough or paddy rice), the kernel is enclosed in a tough siliceous hull that renders it unsuitable for human consumption. Once this hull is removed during processing, the kernel (or caryopsis), comprised of the pericarp (outer bran) and the seed proper (inner bran, endosperm, and germ), is known as brown rice or sometimes as unpolished rice. Brown rice is in little demand as a food. Unless stored under favorable conditions, it tends to become rancid and is more subject to insect infestation than are the various forms of milled rice. When brown rice is milled further, the bran and germ are removed to produce the purified endosperm marketed as white rice or polished rice. Milled rice is classified according to size as head rice (whole endosperm) and various classes of broken rice, known as second head, screenings, and brewer's rice, in order of decreasing size.

Corn. The corn grain is the largest of all cereals (Fig. 2) (35). The kernel is flattened, wedge shaped, and broader at the apex than at its attachment to the cob. The aleurone cells contains relatively high levels of protein and oil. They also contain the pigments that make certain varieties appear blue, black, or purple. Each corn kernel contains two types of starchy endosperms, horny (vitreous) and floury (opaque). The horny endosperm is tightly packed. The starch granules in this region are polyhedral in shape, In dent corn varieties, horny endosperm is located on the sides and back of the kernel and bulges toward the center at the sides. The floury endosperm fills the crown (upper part) of the kernel and extends downward to surround the germ. The starch granules in the floury endosperm are ellipsoidal in shape. As dent corn matures, the endoperm shrinks causing an indentation at the top of the kernel. In a typical dent corn, the pericarp comprises about 6%, the germ, 11%, and the endosperm, 83% of the kernel by weight. Flint corn varieties contain a higher ratio of horny to floury endosperm than do dent corn.

Barley. The husks of barley are cemented to the kernel and remain attached after threshing. The husks protect the kernel from mechanical injury during commercial malting, strengthen the texture of steeped barley, and contribute to more uniform germination of the kernels. The husks are also important as a filtration bed in the separation of extract components during mashing and contribute to the flavor and astringency of beer. The main types of cultivated covered barley, differ in the arrangement of grains in the ear, two-rowed and six-rowed ear. The axis of the barley ear has nodes throughout its length. The nodes alternate from side to side. In the six-rowed types of barley, three kernels develop on each node, one central kernel and two lateral kernels. In the two-rowed barley, the lateral kernels are sterile and only the central kernels develop.

The kernel of covered barley consists of the caryopsis and the flowering glumes (or husks). The husks consist of two membranous sheaths that completely enclose the caryopsis. During development of the growing barley, a cementing substance causing adherence is secreted by the caryopsis within the first two weeks after pollination. The husk in cultivated malting barley amounts to about 8 to 15% of the grain. The proportion varies according to type, variety, grain size, and climatic conditions. Large kernels have less husk than small kernels. The husk in two-rowed barley is generally lower than that in six-rowed barley. As in wheat, the caryopsis of barley is a one-seeded fruit in which the outer pericarp layers enclose the aleurone, the starchy endosperm, and the germ. The aleurone layer in barley is at least two cell layers thick; in other cereal grains (rice excepted), it is one cell layer thick.

Oats. The common varieties of oats have the fruit (caryopsis) enveloped by a hull composed of the floral envelopes. Naked or hull-less oat varieties are known but not grown extensively. In light thin oats, hulls may comprise as much as 45% of the grain. In very heavy or plump oats, the hull may represent only 20%. The hull normally makes up about 30% of the grain. Oat kernels, obtained by removing hulls, are called groats.

Sorghum. Sorghum kernels are generally spherical to flattened spheres, have a kernel mass of 20 to 30 mg, and may be white, yellow, brown, or red. Sorghum has both vitreous and opaque regions within the kernel similar to that of corn. Sorghum grains contain polyphenolic com-


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Figure 1. A wheat kernel. Longitudinal section (enlarged ca 12 X). »Source; Ref. 35.

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