Soluble protein classes
Globulin, the saline-soluble protein, was the major fraction in silflower seed protein and accounted for more than half of the total protein (Table 5). Globulin amount is about 3-fold greater than either water-soluble albumin or alkali-soluble glutelin. The ethanol-soluble fraction (prolamin) was the least at 8.71%. Silflower globulin content compares well with that of sunflower meal protein (40-90%), while its albumin content is also within the range reported for sunflower protein (10-30%) (Gonzalez-Perez and Vereijken, 2007). Glutelin in sunflower is only a minor fraction (Gonzalez-Perez and Vereijken, 2007) but such is not the case for silflower glutelin, which, at 19%, was the second highest content after the globulins. Sunflower globulin and albumin are reported to have glutamic acid-glutamine, glycine, aspartic acid-asparagine, and arginine as the most abundant amino acids (Baudet and Mosse, 1977), but the albumin is also rich in lysine and sulfur-containing amino acids (cysteine + methionine) (Kortt and Caldwell, 1990; Egorov et al., 1996), which globulin lacks. The prolamin fraction generally has glutamine and proline in the greatest amounts, but is deficient in lysine and tryptophan (Shewry, Napier, and Tatham, 1995). Glutelin peptide sequences were reported to be predominantly glutamine, proline and glycine (high molecular weight) or serine, glutamine, proline, and phenylalanine (low molecular weight) (Wieser, Seilmeier, and Belitz, 1988). The amounts of soluble protein classes in silflower seed do not conform to those found in cereals (28% albumins + globulins, 40% glutelins, 33% prolamins) or high-protein seeds (92% albumins + globulins, 7% glutelins, <1% prolamins) (Nikokyris and Kandylis, 1997).