Abstract
In this study, the effects of different extrusion parameters (extrusion temperature: 100, 130, and 160 °C; moisture content: 22%, 26%, and 30%; screw speed: 180 rpm, 270 rpm, and 360 rpm) on physicochemical properties of finger millet were reviewed. High extrusion temperature produced extrudates with high radial expansion index (REI) and starch digestibility and low bulk density (BD). High moisture content and low screw speed increased BD and total starch content (TSC) while decreasing REI and water solubility index (WSI). WSI and starch digestibility first increased and then decreased with increase in extrusion temperature and moisture content, which reached a maximum at 130 °C nd 26%, respectively. However, water absorption index (WAI) was affected by the interactions among various conditions. The extrudates were darker and yellower than native millet. Based on these extrusion conditions, various millet and millet-based products can be produced.
Highlights
Millet, a small-seeded crop of considerable importance in many parts of the world, especially in Asia and Africa, plays a major role in food supply security (Liang et al, 2018)
These results suggested that high extrusion temperature, low moisture content, and high screw speed are critical for attaining high Radial Expansion Index (REI) of extrudates
The main factor responsible for changes in color properties is the Maillard reaction, which is divided into three steps: in the initial phase, in which a reaction between reducing sugar and amines results in colorless products; slightly yellow or colourless products are formed in the middle phase, whereas intense colored products are the outcome of the last phase of the process (Ames, 1998)
Summary
A small-seeded crop of considerable importance in many parts of the world, especially in Asia and Africa, plays a major role in food supply security (Liang et al, 2018). Extrusion parameters such as the screw speed, extrusion temperature, and moisture content can affect the properties of extrudates. Extrusion of decorticated millet at 13-15% moisture content produced expanded extrudates with low bulk density, high water solubility and molecular dispersion of starch. Kharat et al (2019) reported the extrusion processing characteristics of whole grain flours of major millets (finger, foxtail and pearl), and showed that whole grain foxtail millet flour was the best among the three millets tested in their study for expanding the millet-based product repertoire. We investigated the effect of different extrusion conditions (extrusion temperature, screw speed, and moisture content) on physicochemical properties (radial expansion index (REI), bulk density (BD), water solubility index (WSI), water absorption index (WAI), and total starch content (TS)). In order to provide a certain theoretical basis for the development of millet and millet-based food by extrusion
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