Physicochemical properties of tef starch: morphological, thermal, thermogravimetric, and pasting properties

Abstract

ABSTRACT Starches isolated from the tef variety (Quncho) were examined for their physicochemical, morphological, thermal, pasting, and thermogravimetric characteristics. Studies revealed that the Quncho tef and maize starches had moisture, fat, total protein, and ash contents of 8.1, 0.59, 0.02, 0.25, and 5.99, 0.61, 0.01, 0.21 g/100 g, respectively. Quncho tef starch had higher phosphorus content (45.1 mg/100 g sample) than corn starch (40.6 mg/100 g sample). Starch purity of Quncho tef was found to be low (91.6 g/100 g), while corn starch was high (93.6 g/100 g). Amylose contents of Quncho tef starch were observed to be lower (22.2 g/100 g) than those of the corn starch (28.4 g/100 g). Variation of amylose contents significantly affects the physicochemical, morphological, and thermal properties of the starches. Quncho tef starch was low T o , T p , T c , Δ T , and Δ H gel values of 33.3°C, 78.2°C, 125.1°C, 91.8°C, and 1.72 J/g, respectively, while commercial corn starch was high T o , T p , T c , ΔT , and Δ H gel values of 34.7°C, 117.9°C, 179.3°C, 144.6°C, and 5.29 J/g, respectively. The initial, peak, and final thermal degradation of Quncho tef and commercial corn starches were 226.58°C,354.45°C, 384.46°C, and 284.65°C, 417.71°C, 536.01°C, respectively. The maximum weight loss percentages of Quncho tef and corn starches were found to be 80.87% and 89.26%, respectively. The heat degradation of Quncho tef and corn starches was heavily influenced by the ratio of amylose to amylopectin content starch. Corn starch granules appeared oval in shape and irregular in shape under scanning electron microscopy, whereas Quncho tef starch granules appeared polygonal or hexagonal in shape and irregular in shape.