Optimization of single screw extrusion process for producing fish feeds based on vegetable meals and evaluation of nutritional effects using a juvenile Piaractus mesopotamicus model

Optimization of extrusion process for producing extruded feeds based on vegetable meals using a single screw extruder was study. Also growth performance of extruded feed obtained in optimal conditions using a juvenile P mesopotamicus model was evaluated. In order to study the simultaneous effect of blend moisture (M) and extrusion temperature (T) on expansion (E), bulk density (BD), water absorption index (WAI), water solubility index (WSI), and floatability (F) a central composite design (32) was used. The levels of each variable were: T: 160-180-200 °C and M: 14-16-18 g/100 g. A multiple response optimization of physical properties of experimental extruded feed (E, F, BD and WSI) was performed using the Derringer's desirability function. The global desirability function value was 0.8805, and the obtained optimal conditions were 181.5 °C and 15.8 g/100 g of moisture content. Experimental extruded feed (EF) obtained at such conditions presented the following physical properties: E: 2.23 ± 0.03, F: 99.0 ± 1.0%, BD: 270.9 ± 13.8 g/L, and WSI: 12.9 ± 1.5 g/100 g. Crude protein content of EF was higher than that of control feed (CF). However, no significant difference for crude lipid (∼37.9 g/kg) and total starch content was found. Gelatinized starch for EF (430.5 ± 7.0 g/kg) was higher than that obtained for CF (378.9 ± 6.7 g/kg), corresponding to 97.0 ± 2.1 and 88.1 ± 2.2% of degree of gelatinization, respectively. Chemical score of CF was 93.3%, lysine being the limiting amino acid. However, in the case of EF no limiting amino acid was found. Both diets presented a predominance of unsaturated fatty acids of C18 series (C18:1 and C18:2 (n-6)). EF showed higher content of oleic, linolenic, cis-11-eicosenoic and di-homo-γ-linolenic acid than CF. Nevertheless, only for CF, eicosapentaenoic acid, docosapentaenoic, and docosahexaenoic acid were detected. Significant differences in final fish body weight, weight gain, specific growth rate, and condition factor were not detected between dietary treatments after 120 days of feeding trial. Extrusion using a single screw extruder in optimal process conditions could be used to obtain fish feed based in vegetable meals and good physical properties with proper growth performance on juvenile P. mesopotamicus.