The influence of location and spacing of reverse screw element(s) on specific mechanical energy input and product attributes during twinscrew extrusion of rice flour and pink salmon blends was investigated. Incorporation of reverse screw element(s) increased specific mechanical energy, expansion ratio and water solubility index; but decreased bulk density and Warner-Bratzler shear stress. Opposite trend was observed with increasing fish content except for shear stress, which was little affected either for rice flour or its blends with 30% fish solids in the expansion ratio range 5 to 10. Linear relationships were found between shear stress and bulk density and between solubility index and specific mechanical energy.

The effects of extruder length‐to‐diameter (L/D) ratio and barrel temperature on extrusion system parameters and extrudate characteristics during twin‐screw extrusion of rice flour were studied. the L/D ratio and barrel temperature were varied between 16–24 and 75–185C, respectively. the extrusion system parameters studied were thrust bearing pressure and specific mechanical energy. the expansion ratio, bulk density and maximum force of the extruded product, as affected by the L/D ratio and barrel temperature, were investigated. Experimental data on system parameters and extrudate characteristics were fitted to a second degree polynomial. The linear as well as the quadratic effect of L/D ratio, and the quadratic effect of temperature were significant (p < 0.10) in most cases. the significant (p < 0.10) interaction term (L/D ratio *temperature) for most of the response functions revealed that a change in the L/D ratio can affect the influence of temperature on system parameters and extrudate attributes. the hardness of the extrudates increased with increasing L/D ratio. Microstructure of the extrudates suggested that a barrel temperature above 150C is desirable to get an expanded product.

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