Cereal Chem. 73 (6):677-685 |
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Carbohydrates
Structures and Physicochemical Properties of Starches from Acha (Digitaria exilis), Iburu (D. iburua), and Tamba (Eleusine coracana).
I. A. Jideani (1,2), Y. Takeda (1,3), and S. Hizukuri (1). (1) Postdoctoral fellow, professor, and professor, respectively, Department of Biochemical Science and Technology, Faculty of Agriculture, Kagoshima University, Korimoto-1, Kagoshina 890, Japan. (2) Present address: School of Science, Abubakar Tafawa Balewa University, PMB 0248, Bauchi Nigeria. (3) Corresponding author. E-mail: <takeda@chem.agri.kagoshima-u.ac.jp> Accepted July 12, 1996. Copyright 1996 by the American Association of Cereal Chemists, Inc.
Structures and physicochemical properties of starches from three African cereal grains, acha (Digitaria exilis), iburu (D. iburua), and tamba (Eleusine coracana), were determined. The starches were fractionated into amylose and amylopectin. The amylose contents (%), determined from iodine affinity, of acha (18.7), iburu (19.6), and tamba (19.8) starches were similar to those reported for rice (17-19), wheat (21.7), and 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 tamba were small molecules with number-average degree of polymerization (DP(n)) 1,040, 1,120, and 1,420, respectively, each with an average of six chains. Acha amylose had the highest amount of branched molecule (approximately 79 mol%) with lower average number of chain (NC approximately 7) than those of others (53-34 mol%, NC approximately 10-13). The 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 lower breakdown than did the RVA of corn starch. Unlike the other starches, the viscosity of tamba starch did not change during the hold at 92.5ºC. Granules from the three starches were of the A crystalline type, as in those of rice, wheat and corn starches, with diameter in the 2.0-14.3 µm range.