No abstract

No abstract

The effects of 29 screw configurations on rice flour extrudates were investigated. The moisture content, screw speed and feed flow rate during all extrusion experiments were 15%, 400 rpm, and 12kg/h, respectively. Temperature profile in the 8 barrel sections from feed to die end were set at 0, 30, 30, 30, 70, 100, 150, and 1508C. Incorporation of kneading block (KB) and reverse screw element (RSE) in screw profiles significantly influenced apparent density, product expansion (radial, axial and overall), and breaking strength. Apparent density and overall expansion were functions of die temperature. KB was the best element for maximizing radial expansion. Product hardness (breaking strength) decreased with increasing radial expansion.

Screw configuration effects on starch breakdown and extrudate porosity were investigated during twin-screw extrusion of ricepour. The type, length, position, of mixing elements and spacing between two elements significantly affected molecular breakdown of starch in rice flour and extrudate porosity. Generally, screw profiles with reverse screw element produced more starch breakdown and porous extrudates than those with kneading block. A systematic increase of starch breakdown was observed as the mixing elements were moved farther from the die, with longer elements, and with increased spacing between elements. Extent of starch breakdown affected porosity of extrudates. Extrudate porosity decreased systematically with increasing distance between die and mixing element, with larger spacing between the elements, and by moving two elements (with same spacing) farther from the die, irrespective of the element type and length. Porosity increased with increasing die temperature. ' Present address: Wright Enrichment, Inc.,

A technique was based on electrical conductivity of material in a die, and used a series circuit consisting of a 5 mm dia die, a 10 ohm resistor, and a 15V dc power supply. Material conductivity was altered with addition of an electrolyte tracer at the feed inlet. Change in current flow was measured as a proportional voltage response across the resistor. Using a twin-screw extruder, with L/D 32:1, the RTD of rice flour at 15% moisture was determined using sodium nitrate as tracer. Under steady state, the voltage across the resistor was measured. The on-line results correlated well with the established erythrosine dye method. The effects of screw configuration, feed flow rate, and screw speed were precisely determined by the on-line method.