Chemical and physical characterisation of grain Tef [Eragrostis tef (Zucc.) Trotter] starch granule composition

Chemical and physical properties of starch granules isolated from five grain tef (Eragrostis tef) varieties were characterised and compared with those of maize starch. Endogenous starch lipids extracted with hot water-saturated n-butanol and total starch lipids extracted with n-hexane after HCl hydrolysis were 7.8 mg/g (mean) and 8.9 mg/g (mean), respectively, slightly lower than in the maize starch granules. The starch phosphorus content (0.65 mg/g) was higher than that of maize starch but virtually the same as reported for rice starch. The starch granule-swelling factor was lower than that of maize starch and extent of amylose leaching was higher. The starch X-ray diffraction pattern was characteristic of A type starch with a mean crystallinity of 37%, apparently lower than the crystallinity of maize starch and more similar to that reported for rice and sorghum starches. The starch DSC gelatinisation temperature was high, like for other tropical cereals; T-o, T-p, T-c and DeltaH were in the range 63.8-65.4, 70.2-71.3, 81.3-81.5 degreesC and 2.28-7.22 J/g, respectively. The lower swelling, apparently lower percentage crystallinity and lower DSC gelatinisation endotherms than maize starch suggest that the proportion of long amylopectin A chains in tef starch is smaller than in maize starch.