Objective: Hypericum perforatum L. synthesizes hypericin, a bioactive compound with antidepressant and antiviral properties. Optimizing post-harvest processing is crucial to preserve metabolite content, as drying conditions can markedly affect compound stability. This study evaluated the impact of shade-drying, oven-drying, and freeze-drying on hypericin accumulation in adventitious roots of H. perforatum.

Methods: Fresh adventitious roots (~90% moisture, wet basis) underwent shade-drying, oven-drying, or freeze-drying until final moisture reached 37%, 8%, and 5.3%, respectively. Hypericin content was quantified via high-performance liquid chromatography (HPLC). Four independent root lines were analyzed to assess biological variability. Hierarchical cluster analysis with heatmap visualization examined the relationships between drying treatments and root lines.

Results: Drying method significantly influenced hypericin retention. Freeze-drying preserved the highest levels, with peak concentrations of 0.166 mg/g DW, while oven-drying retained intermediate levels and shade-drying caused the greatest losses. Across all drying conditions, line 4 consistently exhibited higher hypericin content, indicating potential genetic or physiological advantages in metabolite biosynthesis or storage. Cluster analysis revealed a clear separation of freeze-dried samples, with line 4 displaying distinctly superior performance.

Conclusion: Freeze-drying is the most effective method for maintaining hypericin in H. perforatum adventitious roots, whereas oven- and shade-drying substantially reduce content. Additionally, root line selection critically affects metabolite accumulation, with line 4 demonstrating the highest potential. These findings highlight that both post-harvest processing strategies and genotype optimization are essential for maximizing hypericin yield in biotechnological and industrial applications.