Effect of larval instar and post-harvest treatments on heavy metals in BSFL and frass reared on commercial food waste streams

The use of black soldier fly larvae (BSFL) to valorise different organic waste streams and the subsequent use of resulting larvae as a feedstock ingredient is increasing rapidly in several regions across the globe. The lack of knowledge about several safety issues including chemical contaminants (e.g. heavy metals) seems to affect the upscaling and commercialisation of this product. This study evaluates the safety of the BSFL against chemical contaminants including heavy metals and mycotoxins in both BSFL and frass samples reared with different food waste streams (e.g. soy waste, customised bread-vegetable diet, food waste mixture, supermarket and childcare centre) from two commercial production facilities. The effect of larval instars and post-harvest treatments (e.g. blanching and drying) on the safety of the BSFL was also investigated. The concentration of heavy metals was primarily influenced by the concentration in the food waste streams. The concentration was also higher in 6th instar compared to 5th instar larvae. The effect of blanching and drying have a varied effect on the concentration of heavy metals. Mycotoxins were found to be below the limit of quantification for all samples. The outcomes of this study indicated that BSFL grown on food waste streams and the resulting frass is safe against different heavy metals analysed. The findings of this study will assist the commercial BSFL manufacturers with the identification of relevant control points to ensure the chemical safety of their products. Therefore, encourage the use of different food waste streams as feedstock for rearing BSFL.