Spent mushroom substrate (SMS) is the nutrient-depleted medium left after the commercial cultivation of protein-rich mushrooms such as Agaricus bisporus and Pleurotus ostreatus, which are typically grown on agricultural byproducts. Often discarded as waste, SMS can be converted through hydrothermal liquefaction (HTL) into liquid and solid products with potential applications as soil amendments, crop fertilizers, or alternative pesticides. In this study, liquid products obtained from the hydrothermal liquefaction (HTL) of spent mushroom substrates from A. bisporus and P. ostreatus cultivations were analyzed using direct-infusion ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry. This technique enables nontargeted chemical fingerprinting of complex organic mixtures such as HTL-derived products. The SMS-derived aqueous HTL products were found to be chemically highly diverse, comprising a broad range of heteroatomic (NOS) compounds, including phenolics, sugars, and lipids, along with their nitrogen- and sulfur-containing derivatives. Elemental analysis of the products revealed significant levels of nitrogen and sulfur, along with several inorganic elements commonly associated with nutrients (e.g., Al, Ca, Fe, K, Mg, and P), as well as trace amounts of some other metals. Comprehensive understanding of the chemical composition of HTL products is essential for their further valorization across different applications.
Eronen et al. (Tue,) studied this question.