Comparative Preservation Methods for Valerian: Effects of Hot‐Air, Infrared, Hybrid, and Shade Drying on Phytochemical Profile, Antioxidant Activity, Essential Oil Composition, and Color Characteristics

Abstract

Drying is a common preservation method for medicinal plants, crucial for maintaining their quality, and bioactivity. This study investigated the impact of various drying methods on the phytochemical profile, antioxidant activity, essential oil composition, and color of valerian, using a completely randomized design. Treatments included hot air drying (40°C, 50°C, and 60°C at 1 m/s), infrared (IR) radiation (0.2, 0.3, and 0.5 W/cm 2 ), a hybrid method (hot air at 50°C combined with IR at 0.3 W/cm 2 ), and shade drying. Key parameters measured were drying time, total phenolic content (TPC), total flavonoid content (TFC), antioxidant activity (DPPH and FRAP assays), essential oil constituents (via GC and GC–MS), and color changes. IR drying at 0.5 W/cm 2 resulted in the shortest drying time (107 min). Higher air temperatures and IR intensities significantly accelerated moisture removal. The highest TPC (72.60 mg GAE/g DW) was observed under IR drying at 0.3 W/cm 2 , while the highest TFC (13.16 mg QE/g DW) was recorded under hot‐air drying at 60°C, followed by IR drying at 0.3 W/cm 2 . Antioxidant activity was also greatest at 60°C, followed by IR drying at 0.3 W/cm 2 . A total of 104 essential oil compounds was identified, with the highest total concentrations of key volatiles—α‐Gurjunene, Alloaromadendrene, Germacrene B, Valerenal, and Bornyl acetate—found in IR drying at 0.5 W/cm 2 . Color difference analysis indicated that samples dried at 40°C and IR at 0.5 W/cm 2 exhibited superior color preservation. Overall, IR drying (at 0.3 or 0.5 W/cm 2 ) was most effective for preserving essential oils, reducing drying time, and maintaining phytochemical and antioxidant qualities. The results offer valuable implications for the medicinal plant sector by guiding the selection of drying methods aligned with desired bioactive profiles. Future studies are recommended to assess the scalability, energy efficiency, economic feasibility, and sustainability of optimized infrared and hybrid drying technologies at an industrial level.