INFLUENCE OF PROCESS VARIABLES ON THE CHARACTERISTICS OF A HIGH-MOISTURE FISH SOY PROTEIN MIX TEXTURIZED BY EXTRUSION-COOKING

A two-level factorial experimental design was used to study the influe nce of process variables (feed rate, 33 - 38 kg/h; screw speed, 70 - 1 00 rpm; extruder barrel temperature, 173 - 177 degrees C; feed moistur e, 630 - 650 g/kg) on the resistance to stretching, colour and final w ater content (after immersion in water) of extrudates from a mix of fi sh surimi and soy protein concentrate texturized by extrusion cooking. The relationship between process variables and system parameters (pro duct temperature before the cooling die, mean and peak residence times in the extruder + die) was also investigated. Extrusion cooking was c arried out on a long barrel (1500 mm) co-rotative twin screw extruder equiped with an 800 P 40 P 3 mm cooling die. Extrudate texture was fou nd to depend mainly on feed moisture, screw speed and barrel temperatu re, in this decreasing order. Extrudate colour depended most significa ntly on feed moisture and barrel temperature, while the final water co ntent of extrudates (after immersion in water) was most affected by ba rrel temperature and screw speed, Within the experimental domain, the Seed rare and mean residence time had no significant effect on the cha racteristics of extrudates. (C) 1996 Academic Press Limited