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초록

The operational conditions of a twin-screw extruder were optimized for the extrusion of a Tartary buckwheat(Fagopyrum tataricum) flour to impart the additional water solubilities into the products. The extrudates were thenanalyzed using a Response Surface Analysis to extract correlation between the system variables such as specificmechanical energy (SME) and extrusion pressure of the extruder and some physical characteristics of the productsincluding bulk density and water solubility index (WSI) value of the extrudates as influenced by barrel temperature(120, 150, 180oC) and moisture content (20~30%) of the feeds. Whereas effects of shear rates in the system as gov-erned by screw configurations (type I~IV) were further evaluated in relation to the quality characteristics of theextrudates. Decreases in SME value and were observed with increase of the barrel temperature, while WSI value of the extrudate increased. However, thehigher SME value and extrusion pressure of the system accompanied by WSI of the product were observed as mois-ture content of the feed has decreased although density of the extrudate was the exception. Adoption of the screwconfigurations that is designed to give higher shear rate resulted in the decrease of extrusion pressure and densityof the products although SME of the system and WSI of the extrudates tended to increase. Purposed extrusion ofthe Tartary buckwheat (F. tataricum) with barrel temperature at 180 and feed moisture content of 20% could raiseWSI value of the product up to 24.3% as compared to that of 2.5% in raw buckwheat flour. Furthermore, whenscrew configuration of KD/LH (kneading disc/left handed rotating) with type IV layout that gives the highest shearrate in this system was introduced, WSI value of the extrudate has increased again up to 33.8%.

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