The Prolamin Storage Proteins of Sorghum and Millets

Most millets are classified with maize, sorghum and Coix (Job's tears) in the grass sub-family Panicoideae, but two species, tef and ragi (finger millet) are placed in a separate sub-family, the Chloridoideae. In all species the major storage proteins are alcohol-soluble prolamins, but their properties vary. For example, although the kafirins of sorghum are closely related to the zeins of maize, they differ in their solubility properties, being more efficiently extracted with 60% (v/v) tertiary butanol, a less polar solvent than propan-2-ol. Maize prolamins are classified into four groups, termed alpha-, beta-, gammaand delta-zeins. Of these, the alpha-zeins are the major fraction but have low nutritional quality, with low contents of cysteine and methionine and no lysine or tryptophan. In contrast, the beta-zeins and delta-zeins contain about 11 mol% and over 20 mol% methionine, respectively.