STRUCTURES AND PHYSICOCHEMICAL PROPERTIES OF STARCHES FROM ACHA (DIGITARIA-EXILIS), IBURU (DIGITARIA-IBURUA), AND TAMBA (ELEUSINE-CORACANA)

Structures and physicochemical properties of starches from three Afric an cereal grains, acha (Digitaria exilis), iburu (D. ibunra), and tamb a (Eleusine coracana), were determined. The starches were fractionated into amylose and amylopectin. The amylose contents (%), determined fr om iodine affinity, of acha (18.7), iburu (19.6), and tamba (19.8) sta rches were similar to those reported for rice (17-19), wheat (21.7), a nd corn (21.5) starches. The values of iodine affinity (IA) (g/100 g), blue value, and lambda(max) (nm) obtained for the three starches fall within the range reported for most cereals. Analyses of reducing and nonreducing residues showed that the amyloses of acha, iburu, and tamb a were small molecules with number-average degree of polymerization (D Pn) 1,040, 1,120, and 1,420, respectively, each with an average of six chains. Acha amylose had the highest amount of branched molecule (app roximate to 79 mol%) with lower average number of chain (NC approximat e to 7) than those of others (53-34 mol%, NC approximate to 10-13). Th e amylopectins from the three cereals had IA values of 1.3-1.5 g/100 g , average chain lengths of 20-21, and beta-amylolysis limits of 60-62% , which are similar to those of the rice and corn amylopectins. Rapid viscograph analysis (RVA) at 9% (w/w) starch suspension of acha, iburu , and tamba showed a lower peak pasting viscosity and considerably low er breakdown than did the RVA of corn starch. Unlike the other starche s, the viscosity of tamba starch did not change during the hold at 92. 5 degrees C. Granules from the three starches were of the A crystallin e type, as in those of rice, wheat and corn starches, with diameter in the 2.0-14.3 mu m range.