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Effects of Thermomechanical Extrusion and Particle Size Reduction on Bioconversion Rate of Corn Fiber for Ethanol Production

Lin, Myat, Ryu, Gi-Hyung
Cereal chemistry 2014 v.91 no.4 pp. 366-373
amino nitrogen, biotransformation, color, corn, digestible protein, ethanol, ethanol production, extrusion, fermentation, melting, particle size, starch, temperature, water content, water solubility
The objective of this research was to evaluate the effect of thermomechanical extrusion and particle size (PS) reduction on the bioconversion rate of corn fiber for ethanol production. Extrusion was conducted at a screw speed of 300 rpm, feed rate of 120 g/min, feed moisture content of 30%, melt temperature of 140°C, and die diameter of 3 mm. Raw and extruded corn fiber were separated into three different PSs (1 > PS ≥ 0.5, 0.5 > PS ≥ 0.3, and 0.3 > PS ≥ 0.15 mm) with a wire sieve. Extrusion pretreatment and PS reduction resulted in a significant (P < 0.05) difference in physical properties and color values of extruded corn fiber as a result of accelerated degradation of corn fiber structure. Significant increase in water solubility index of extruded corn fiber at 0.3 > PS ≥ 0.15 mm was an indication of high degradation of starch during extrusion for higher release of polysaccharides. Moreover, extruded corn fiber at PS reduction 0.3 > PS ≥ 0.15 mm also significantly increased (P < 0.05) ethanol yield (69.11 g/L) and conversion (68.18%) by increasing protein digestibility and free amino nitrogen, which are essential for higher fermentation efficiency.