Changes in water absorption and swollen volume in extruded alkaline peroxide pretreated rice hulls
1997
Larrea, M.A. | Grossmann, M.V.E. | Beleia, A.P. | Tavares, D.Q.
Rice hulls were pretreated with an alkaline (pH 11.5) solution of hydrogen peroxide (1%) and then extruded. Pretreatment of rice hulls (4% db) at 50 degrees C for 12 hr promoted 94.4% silica reduction, caused lignin solubilization and increased water absorption index (54%) and swollen volume (44%). The effects of temperature (125, 175, and 225 degrees C), moisture content (25, 30, and 35%) and screw speed (120, 140, and 160 rpm) on water absorption and swollen volume of rice hulls fiber were evaluated after extrusion in a single-screw extruder. Operational conditions that produced the most modified product with regard to the functional properties were: 125 degrees C, 35% moisture, and 120 rpm. Extruded fiber had a water absorption index 95% higher and swollen volume 138% higher than the unprocessed material. Microscopic examination showed a slight effect on the hulls epidermis after pretreatment, while extrusion promoted cellular structure disruption.
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