Extruded fish feed with high residual phytase activity and low mineral leaching increased P. mesopotamicus mineral retention

This study attempts to provide valuable information about optimization of extrusion process in order to have a fish feed with maximum residual phytase activity, minimum mineral leaching and good mechanical characteristics. Also, the effects on mineral retention of extruded feed obtained in optimal condition, using a juvenile Piaractus mesopotamicus model was determined. In order to study the simultaneous effect of blend moisture (M) and extrusion temperature (T) on specific volume (SV), water resistance (WR), floatability (F), residual phytase activity (RPA), leached phosphorus (LP), calcium (LCa), zinc (LZn), and iron (LFe) a central composite design (32) was used. The levels of each variable were: T: 160-180-200 °C and M: 140-160-180 g/kg. A multiple response optimization of physicochemical properties of extruded feed (WR, F, RPA and mineral leaching) was performed using the Derringer's desirability function. The global desirability function value was 0.8990, and the obtained optimal conditions were 183.6 °C and 158 g/kg of moisture content. Phytase extruded feed (PEF) was obtained at such conditions and it had the following physical properties: WR: 81.8 ± 2.5%, F: 94.5 ± 0.72%, LP: 9.40 ± 0.61%, LCa: 2.20 ± 0.2%, LZn: 2.00 ± 0.15%, and LFe: 11.2 ± 2.8%. Fish consuming PEF with RPA of 3934.9 ± 47.7 UP/kg had higher iron, zinc, and phosphorus retention than those fed with control extruded feed (CEF) obtained under the same optimal conditions (p < 0.05). However, no significant difference in final body weight was detected between dietary treatments (p > 0.05) after 38 days of feeding trial at 25 °C. Extrusion process can be optimized to obtain fish feed based on vegetable meals with high residual phytase activity and low mineral leaching, increasing P. mesopotamicus mineral retention.