Effects of extruding wheat flour under different temperature and humidity conditions on its biochemical analysis, phenolic compounds and digestibility by common carp (Cyprinus carpio)

The extrusion process is widely used in making aquatic feeds. The aim of this study was to investigate the effects of extrusion on biochemical analysis, removal of phenolic compounds and protein and carbohydrate digestibility of wheat flour in common carp. In treatments 1, 2 and 3 wheat flour was mixed with tap water at the rate of 250, 100 and 200 ml per kg of flour and then extruded by a single-axis extruder under the temperature of 120, 135 and 120 °C, respectively. Treatment 4 (control) was not subjected to the conditions of dough preparation and then extrusion. Extruding had no significant effect on the amount of crude protein and ash of wheat flour (p>0.05) but it significantly decreased the content of crude lipid, total phenolic compounds and non-tannin phenolic compounds and increased the digestibility of carbohydrate and protein (p<0.05). There were no significant differences in the amount of crude protein, crude lipid, ash and non-tannin phenolic compounds in the extruded treatments, but significantly the lowest amount of total phenolic compounds was recorded in treatments 1 and 2. Significantly, the highest carbohydrate digestibility was obtained in treatments 1 and 2, and the highest protein digestibility was observed in treatment 2. In total, treatment 2 (135 °C and 100 ml tap water per kg flour) was recognized as the best extruded wheat flour for common carp.