TWIN SCREW EXTRUSION OF PINK SALMON MUSCLE: EFFECT OF MIXING ELEMENTS AND FEED COMPOSITION

The effects of type of mixing element in the screw configuration and feed composition on specific mechanical energy input and product attributes during twin-screw extrusion were investigated. The mixing elements studied were kneading, reverse screw and combination of kneading and reverse screw elements. The feed composition was changed by altering the ratio of rice flour to pink salmon muscle. Incorporation of mixing elements increased the specific mechanical energy, and water solubility index; but decreased apparent density and Warner-Bratzler shear stress. Expansion ratio was maximum with kneading elements. However, reverse screw and combination produced extrudates with lesser expansion than that obtained using conveying screws with no mixing element. Increasing the fish solids content in the feed decreased specific mechanical energy, expansion ratio, and water solubility index; but increased the shear stress and apparent density. The shear stress for 0% and 30% fish solids blends were not affected in the expansion ratio range of 3 to 10. Water solubility index and shear stress were linearly related to specific mechanical energy and apparent density respectively.