Microfungi, Mycotoxins and Heavy Metals in the Mass Rearing of Tenebrio molitor L. Larvae

Since Tenebrio molitor L. was approved by the EU as novel food in 2021, food safety is paramount for both chemically and microbiologically safe products. Since T. molitor larvae are reared on substrates mainly based on cereals, mycotoxins and heavy metals may represent a serious risk. However, analyses of mycotoxins and heavy metals are complex and cost-intensive procedures, which may not be affordable for small-scale farmers on a regular basis. To provide a preliminary risk assessment and to add further insights to existing knowledge, this study used a rapid screening method based on MALDI-TOF to identify potentially mycotoxin-producing microfungi. The colony-forming units (CFU) were determined, and the isolated species identified. In addition, a_w-values of substrates and meal (four samples, nine repeats each) were determined to assess mycotoxin-related risks. Eight mycobionts were identified, including three potential mycotoxin producers: Penicillium citrinum, Aspergillus flavus, and Aspergillus brasiliensis. Very low CFU counts (<3 × 10³ CFU/g) and a_w-values (0.35-0.59) indicate minor risks. LC-MS/MS mycotoxin analysis of nine samples (varying in source and time point) confirmed concentrations below the limit of detection (LoD): 0.50 µg/kg for aflatoxins B1/B2/G1/G2; 50 µg/kg for DON/FuB1/FuB2; 20 µg/kg for HT2/T2; 150 µg/kg for NIV; 1 µg/kg for OTA; and 5 µg/kg for ZEA. Heavy metal analysis (ICP-OES/MS) of three substrates and insect meal showed that all six metals (Cd, Pb, Hg, Sb, As, Cr) were below the LoD (0.2 mg/kg), except for Cr in malt residual pellets (0.4 mg/kg).