Feeding black soldier fly (Hermetia illucens) larvae with mushrooms and then exposing them to UVB produces larvae extremely rich in vitamins D2 and D3

• BSFL bioaccumulate ergosterol when reared on mushrooms. • UVB exposure of ergosterol-enriched BSFL allows to obtain vitamin D 2 -rich BSFL. • Enriching BSFL with ergosterol before UVB exposure enhances their vitamin D 3 production. • UVB exposure of ergosterol-enriched BSFL produces 46 and 11 mg/kg of vitamin D 2 and D 3 . • Total vitamin D concentration in BSFL was 23 times higher than that observed in cod liver oil. Black soldier fly larvae (BSFL) are a sustainable source of protein for feed but they can also be a sustainable source of some phytochemicals due to their ability to bioaccumulate them. Knowing that ergosterol in mushrooms can be chemically converted to vitamin D 2 (VD 2 ) under ultraviolet B (UVB) exposure, the aim was to investigate whether BSFL can bioaccumulate ergosterol and whether larvae ergosterol can be converted into VD 2 under UVB exposure. BSFL were reared on mushrooms for 2 weeks and then exposed to UVB (2.7 mW/cm 2 /s for up to 5 h). Ergosterol, VD 2 and vitamin D 3 (VD 3 ) were quantified by HPLC in mushrooms and larvae. larvae non-exposed to UVB did not contain any detectable amount of VD 2 or VD 3 . Larvae reared on mushrooms bioaccumulated ergosterol (702 ± 95 mg/Kg FW in larvae vs 444 ± 56 mg/Kg in mushrooms). Larvae reared on mushrooms and then exposed to UVB for 1 h contained high concentrations of VD 2 but also of VD 3 (46 ± 2 and 10.9 ± 0.5 mg/Kg FW, respectively). BSFL can bioaccumulate ergosterol. UVB exposure of ergosterol-enriched BSFL results in VD 2 but also in VD 3 rich BSFL. The maximal VD concentration obtained in BSFL was about 23 times higher than cod liver oil, the food known to be richest in VD. These results suggest that VD-enriched BSFL could be used to supplement the nutrition of certain livestock with VD, or be valued as a functional ingredient. This procedure has been patented (PCT/EP2024/074854).