Yield, Nutritional Quality, and Microbial Safety of Microgreens Grown in Insect Frass and Vermicompost-Based Growing Substrates

Microgreens have gained increasing popularity due to their cooking versatility, ease of cultivation, and high nutritional value. The use of alternative organic substrates, such as vermicompost and insect frass, offers a promising alternative to peat. This study has evaluated the integration of Tenebrio molitor and Hermetia illucens frass, along with vermicompost, in a microgreen production, while assaying several concentrations (25%, 50%, 75%, and 100%) as replacements by weight. After a preliminary assay aimed at determining the optimal frass and vermicompost levels, we assessed the agronomic, nutritional, and microbiological performances of microgreens. The preliminary results revealed phytotoxic effects of T. molitor frass, while the addition of H. illucens frass or vermicompost did not significantly impact microgreen production. In the second experiment, the interaction between plant species and substrate composition significantly influenced the leaf area, plant height, and mineral content. Partial replacement of peat with H. illucens frass or vermicompost enhanced leaf area and plant height, with a notable increase in iron content in the mizuna microgreens grown with H. illucens frass, compared to the control with peat. Additionally, microbiological safety was ensured, and a complete absence of Salmonella spp. and E. coli was observed in the plants, in accordance with European food safety regulations.