This study examined the effects of pre-soaking solvents and repeated steaming-drying (SD) cycles on the antioxidant activity and active compound content of Rehmanniae Radix Preparata(RRP), the processed root of Rehmannia glutinosa Libosch. SD treatments were conducted for 1 to 9 cycles using four different pre-soaking solvents: Takju (a traditional rice wine), Spirits, Honey, and Sugar solution. The results showed no significant differences in DPPH and ABTS radical scavenging activities or in total polyphenol and flavonoid contents among the pre-soaking treatments, although samples pre-soaked in honey and Takju exhibited slightly higher levels. Polyphenol and flavonoid contents increased progressively with the number of SD cycles, reaching levels 2–3 times higher after nine cycles. Catalpol content remained relatively constant regardless of treatment, whereas aucubin content increased in all groups, with the highest accumulation observed in the Takju treatment. Similarly, 5-hydroxymethylfurfural (5-HMF) content increased with the number of SD cycles, with the highest levels found in the honey group, followed by Takju, Sugar, and Spirits. In conclusion, while the type of pre-soaking solvent had minimal influence on antioxidant activities and catalpol content, both aucubin and 5-HMF contents increased with additional SD cycles, with Takju proving particularly effective in enhancing their accumulation.

Abstract
Introduction
Materials and Methods
    1. Experiment materials
    2. Rehmanniae Radix Preparata preparation
    3. Antioxidant activity (ABTS and DPPH)
    4. Total polyphenol and flavonoid contents
    5. Analysis of major components of R. glutinosa
    6. Statistical analysis
Result and Discussion
References

• Chang Keun Kang(Professor, College of Veterinary Medicine, Gyeongsang National University, Jinju, 52828, Korea)
• Jong Hyuk Kim(Ph.D. Candidate, Department of Applied Life Science, Gyeongsang National University, Jinju 52828, Korea.)
• Se Hee Jeon(The Junior Researcher, Medicinal Resources Research Institute of Gyeongsangnam-do Agricultural Research and Extension Services, 50005, Korea)
• Il Rae Rho(The Master’s Course Student, Department of Applied Life Science, Gyeongsang National University, Jinju 52828, Korea, Professor, Institute of Agriculture and Life Science, Gyeongsang National University, Jinju, 52828, Korea) Corresponding author
• Yeon Ju Lee(The Master’s Course Student, Department of Applied Life Science, Gyeongsang National University, Jinju 52828, Korea)
• Ye Rin Kim(The Master’s Course Student, Department of Applied Life Science, Gyeongsang National University, Jinju 52828, Korea)
• Seung Han Cho(The Master’s Course Student, Department of Applied Life Science, Gyeongsang National University, Jinju 52828, Korea)
• Ju Hyeon Ha(The Master’s Course Student, Department of Applied Life Science, Gyeongsang National University, Jinju 52828, Korea)
• Seo Young Mun(The Master’s Course Student, Department of Applied Life Science, Gyeongsang National University, Jinju 52828, Korea)