Wheat composition: an introduction Wheat is one of the major grains in the diets of about a half of the world’s population and therefore has an important impact on their nutritional quality. Like other typical cereal grains, the wheat kernel contains three main anatomical parts – the embryo, the endosperm and the pericarp, which covers the endosperm.
The outermost bran layers, representing the pericarp, are fi bre rich. Starch and proteins are concentrated in the endosperm, while the germ is high in fat. The bran and germ fractions are also high in vitamins and minerals. The nutritional role of wheat constituents needs particularly to be taken into account when designing a process to transform wheat into bakery products. Table 1.3 indicates fairly typical chemical constituent distributions in the wheat kernel.
It must be realized, however, that these values are indicative, and that the actual composition may vary above or below these fi gures depending on the genotype (variety) (Hinton, 1953; MacMasters et al., 1971; Morrison, 1978; Belitz et al., 2009), and the milling process used, an evolution of which is illustrated in Fig. 1.4 with a further description in Section 1.6.1 (Historical background). At maturity, the wheat kernel consists of 85 % (w/w) carbohydrates (of which about 80 % is starch) found only in the starchy endosperm.
Wheat also contains mono-, di- and oligosaccharides at a level of 7 %, mainly concentrated in the aleurone layer. Fructans are also presents in the starchy endosperm and embryonic axis, while 12 % of the wheat kernel consists of cell wall polysaccharides, which are found in all kernel tissues (Henry and Saini, 1989; Knudsen, 1997; Bruce and Matthew, 2009). Wheat carbohydrates have been studied extensively over the years in terms of structure and functionality as related to particular end-products like bread and bread-type products.