Bruce Stone (Deceased), Department of Biochemistry, La Trobe University, Bundoora, Victoria, Australia; Matthew K. Morell, CSIRO Food Futures Flagship, Canberra, ACT, Australia
WHEAT: Chemistry and Technology, Fourth Edition
Pages 299-362
DOI: https://doi.org/10.1094/9781891127557.009
ISBN: 978-1-891127-55-7
Abstract
The carbohydrate components of cereal grains (caryopses, seeds, kernels) are derived from precursors generated by photosynthesis in the chlorophyll-containing cells of leaves, stems, and the outer integuments (seed coat, palea, and lemma) of the developing grain, which are transferred (translocated) from these tissues through the vascular system to the ripening grain.
The histological composition of mature wheat grain is shown in Table 9.1. At maturity, the wheat (Triticum aestivum) grain consists of 85% (w/w) carbohydrate (of which ∼80% is starch), found only in the starchy endosperm; ∼7% low molecular mass mono-, di-, and oligosaccharides (present in the aleurone, starchy endosperm, and tissues of the embryonic axis) and fructans (present in the starchy endosperm and embryonic axis); and ∼12% cell wall polysaccharides (found in all tissues) (Table 9.2). Functionally, the starch and fructans are polymeric storage forms of carbohydrate that are mobilized by the germinating grain as carbon and energy sources for the developing embryo. Starch from wheat and other cereal grains is the predominant source of human dietary carbohydrate, is the substrate for production of alcoholic beverages by fermentation, and has many industrial uses. Polysaccharides are the chief structural elements of the walls surrounding the protoplasts of all cells of the various tissues making up the grain (Fig. 9.1) (Chapter 3). The cell wall polysaccharides are important in human nutrition as sources of dietary fiber, have antinutritional activities in monogastric animal diets, and have important impacts on grain utilization and end-use quality.
