Effects of hydrolysed fish muscle on intermediate process variables during twin-screw extrusion of rice flour

Abstract

The effects of fish protein hydrolysis time and fish solids level on energy input, residence time, and die temperature during twin-screw extrusion of rice flour and fish muscle blends were investigated. Arrowtooth flounder muscle was autolysed for upto 15 min using muscle-bound protease, hydrolysed muscle was recovered, dried, blended with rice flour at 0, 5, 10, and 15 g/100 g levels, and extruded using a twin-screw extruder. Hydrolysis of arrowtooth muscle beyond 5 min had very little effect on energy input, residence time, mixing index and die temperature. Fish solids level played a dominant role in lowering specific mechanical energy input, raising the mean residence time, and reducing mixing. The effect on die temperature was different for unhydrolysed and hydrolysed fish muscle. The material temperature in the die was strikingly higher and increased with increasing level of hydrolysed fish solids in the blends. Opposite trend was observed for blends with unhydrolysed fish solids.