Abstract

In the valorization of organic waste within circular bioeconomy frameworks, compost and insect frass are increasingly used as soil amendments, yet their molecular composition and the metabolic signatures of biological processing remain poorly characterized. In this study, high-resolution magic angle spinning (HRMAS) nuclear magnetic resonance (NMR) was applied to intact compost and frass samples to explore their metabolic profiles and assess the potential of this technique to detect bioindicators of vermi- and insect-associated biotransformation without destructive sample preparation. HRMAS NMR experiments included water-suppressed one-dimensional 1H spectra and selected two-dimensional experiments (1H–13C HSQC and 1H–13C HMBC) to support signal assignment. The analysis revealed clear differences between compost with and without vermicomposting activity, with low-molecular-weight resonances assigned to glycine betaine (betaine), a characteristic metabolite associated with biotransformation. In Tenebrio molitor frass, 1H-HRMAS spectra displayed a distinct set of small-molecule signals, including betaine resonances detected for the first time in this matrix. Time-resolved monitoring showed that betaine signals remained stable during the studied period. These findings demonstrate that HRMAS NMR provides a minimally invasive, versatile platform for direct characterization of compost and frass, supporting the identification of metabolic signatures linked to vermi- and insect-mediated processing.

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