Integrated Metabolomics of Processing Residues from Camphora officinarum c.t. Borneol as a Potential Substrate for Edible Fungi Cultivation

Background: The residues of Camphora officinarum c.t. borneol after essential oil extraction are often discarded, causing resource waste and environmental pollution, while the edible fungi industry is facing a shortage of traditional cultivation substrates. Methods: This study integrated UPLC-MS/MS and GC-MS to comprehensively profile volatile and non-volatile metabolites. Samples included fresh branches and leaves (ZSXY) and residues after steam distillation (ZSZL), boiling combined with distillation (ZSSZ), and sun-drying after distillation (ZSSG). Results: In total, 2454 metabolites across 25 categories were detected. PCA revealed clear separation between fresh samples and all processed samples, with ZSZL and ZSSZ exhibiting similar metabolic profiles that were distinctly separated from ZSSG. Compared with ZSXY, most metabolites decreased after processing. ZSSG exhibited the strongest degradation, with 1408 down-regulated and only 146 up-regulated metabolites, and total terpenoid content decreased by 92.27%. ZSZL retained the highest levels of nutrients (e.g., amino acids and nucleotides) and bioactive compounds (e.g., phenolic acids, flavonoids, terpenoids), with 322 up-regulated metabolites. Among the specific comparisons, 113, 212, and 487 differentially accumulated metabolites were identified in ZSXY vs. ZSZL, ZSXY vs. ZSSZ, and ZSXY vs. ZSSG, respectively. KEGG enrichment revealed distinct pathway alterations: monoterpenoid degradation and biosynthesis pathways were activated in ZSZL, nitrogen metabolism-related pathways were disturbed in ZSSZ, and both limonene and pinene degradation and aminoacyl-tRNA biosynthesis pathways were enriched in ZSSG. Conclusions: Based on metabolomic profiling, steam distillation residues exhibited favorable retention of nutrients and bioactive compounds, whereas sun-drying led to excessive metabolite loss. These findings support the valorization of processing residues and promote circular agriculture. However, whether these residues can serve as effective substrates for edible fungi cultivation remains to be tested in dedicated cultivation trials.