Fatty acid profile of black soldier fly larvae and frass as affected by different growing substrates

This study aimed to evaluate how different food wastes used as growth substrates affected the lipid composition of Hermetia illucens larvae; the relationship among substrates, larvae, and frass fatty acid (FA) composition was studied. Six thousand five-day-old Hermetia illucens larvae were allotted to one of four different substrates named CTRL (a control substrate made of broiler feed), V50 + B50 (vegetable and butchery wastes, 1:1 ratio), V75 + B25 (vegetable and butchery wastes, 3:1 ratio), and V100 (entirely composed of vegetables). Lipids were extracted from substrates, larvae, and frass separately and the FAs were quantified. Saturated FAs (SFAs) prevailed in all the groups. The CTRL larvae had the highest SFA (64.3%), while the V100 and V50 + B50 larvae had the lowest percentages. The V100 frass recorded a significantly higher SFA value (44.8%) than the others. Lauric acid (C12:0) was high in CTRL (0.2%) and V100 (0.3%) substrates and amount at 7.6 and 9.6% in their correspondent frass, respectively. However, C12:0 content was higher in the CTRL larvae than in the V100 ones (36.7 and 24.5%, respectively), while it had an intermediate value (28.9%) in the V75 + B25 larvae. Finally, the n-3 polyunsaturated FAs (PUFAs) level was high in the V100 substrate and larvae but not in the V100 frass. The relationship between frass FAs and their correspondent amounts in substrates and larvae was significant for C12:0, C18:2n-6, MUFAs, and n-6 PUFAs. There was a positive relationship for C12:0 and MUFAs with both substrates and larvae, while for C18:2n-6 and n-6 PUFAs, the relationship was positive for substrates but negative for larvae. In conclusion, the V100 substrate appeared to be the most suitable treatment for rearing Hermetia illucens because of the positive effects on the fatty acid content of larvae (low SFA and high n-3 PUFA content) and frass (optimal lauric acid levels for fertilizers).