Influence of different growing substrates and processing on the nutrient composition of black soldier fly larvae destined for animal feed

Because of the ongoing depletion of fish stocks and thus continuously rising prices for fish meal, substitution possibilities are in demand. However, since alternate protein sources from plants are mostly of lower protein quality, feedstuff produced from the black soldier fly (BSF) larvae, Hermetia illucens, are considered promising alternatives. Hence, this study investigated the influence of different growing substrates on the crude nutrient and mineral composition of BSF larvae. The three tested substrates were a mixture of middlings (control group), dried distillers’ grains with solubles (protein group), and dried sugar beet pulp (fibre group). After a 15 day growing period, the total larvae yield of the control, protein and fibre groups amounted to 2.58, 0.93 and 0.43 kg wet mass, respectively, the crude protein content reached 37.2, 44.6 and 52.3% of dry matter (DM), respectively. Despite a relatively low methionine content of the BSF meal when compared to fish meal, it showed a good overall protein quality. Furthermore, the BSF meal contained about 50% less P than fish meal. Moreover, an accumulation of undesirable substances like heavy metals may occur and should be monitored during production. Because a lower fat content of BSF larvae would simplify further processing, in a second trial larvae yielded from the control group were pressed using 12 different conditions: pressures of 250 or 450 bar and temperatures of 50 or 60 °C, applied over 10, 20 or 30 min. The best fat reduction from 30.8 to 16.6% of DM was achieved by pressing at 250 bar, 50 °C and 30 min. In conclusion, the total yield of BSF larvae and their ingredients were highly influenced by the used growing substrates. Generally, a BSF meal could crucially contribute to substitute fish meal in animal nutrition.