Inclusion of Hermetia Illucens larvae or prepupae in an experimental extruded feed: process optimisation and impact on in vitro digestibility

This study investigated the effect of extrusion on digestibility of different blends containing Hermetia illucens (HI) larvae or prepupae. Five blends of HI larvae or prepupae and wheat flour, in a ratio of 25:75, with or without sunflower oil addition, have been formulated as follows: prepupae + wheat (no oil); prepupae + wheat (low oil); prepupae + wheat (medium oil); prepupae + wheat (high oil); larvae + wheat (no oil). Ether extract (EE) content in different blend was 31.5, 38.9, 46.3, 53.7 and 46.27 g kg−1 on wet basis (wb), respectively. Blends were homogeneous for moisture (238.9 g kg−1) and crude protein (112.6 g kg−1 wb). Feed blends were extruded by a co-rotating, conical twin-screw mini extruder and net torque value (NTV) was recorded as indicator of extrudability. The best performing blend was furtherly tested at four barrel temperatures (60, 70, 80 and 90 °C). In vitro organic matter digestibility (OMD) and in vitro crude protein digestibility (CPD) were measured to evaluate the effect of extrusion process on nutritional value. Increasing the blend EE content up to 53.74 g kg−1 wb, NTV was reduced by four times (<100 Ncm) compared to 31.5 and 38.9 g kg−1 wb EE blends. The best performing mixture was larvae + wheat (no oil). Extrusion process increased OMD but not CPD compared to unextruded control, while different extrusion temperature did not affect OMD nor CPD. Concluding, extrusion can contribute to increase OMD in insect containing feed blends. EE content in the blends is a key variable that should be defined in the process.