Cereal starch granule development and composition

Abstract

Abstract According to the classical texts (Banks and Greenwood 1975; Whistler et al. 1984; Kainuma 1988) cereal starches are composed of two types of polysaccharide, amylopectin and amylose, and little attention is given to the minor components of the granules such as the integral proteins and lipids. The integral proteins consist of a major polypeptide (58–60 kDa) identified as granule-bound starch synthase, with traces of polypeptides of higher molecular weight (Echt and Schwarz 1981; Sano 1984; Goldner and Boyer 1989). The major integral protein (the so-called waxy protein) is generally determined by a single gene (Wx), and in the waxy mutants of the diploid cereals where the gene (wx) is not expressed there is no detectable waxy protein and typically less than 2 per cent amylose (Villareal and Juliano 1986; Goldner and Boyer I 989). In the triploid endosperm intermediate states between normal (Wx Wx Wx) and waxy (wx wx wx) are possible, and both Wx Wx wx and Wx wx wx genotypes have slightly less waxy protein and amylose than in the normal starches (Nelson 1980).