Development and Comparison of Drying Tropical Herbal Strategies for Annona muricata Leaves: Integrating of Effective Moisture Diffusivity Using Antioxidant Activity, FTIR Ratios, and Color Attributes

Drying strategy employed exerts a significant influence on the kinetics and functional quality of Annona muricata (soursop) leaves. However, the current literature offers a paucity of practical, non-destructive indicators to inform process decisions. The present study sets out to compare sun drying (SD), room-temperature drying (RTD), convective tray drying (CTD; 40 - 60 °C), and microwave drying (MWD; 120 - 380 W), models thin-layer curves, and integrates effective moisture diffusivity (Deff) with quality metrics - antioxidant activity (IC50, DPPH), FTIR ratios (RQ, R1 - R3), and color attributes (ΔE, a*). Multi-parameter models have been shown to outperform simpler forms. The Midilli model provided the most precise global fit (R2 > 0.95; RMSE < 0.05), while Jenna-Das performed well in specific convective subsets. As the temperature/power were increased, Deff increased and reached a peak at an MWD of 380 W. This resulted in an approximate acceleration of ~225× compared to the CTD 50 °C and a drying time of approximately ≈ 4 min. A clear trade-off emerged: CTD 40 °C exhibited a preserved appearance (ΔE ≈ 2.7) but under-retained phenolics (weaker IC50), whereas CTD 60 °C and MWD 380 W produced higher ΔE (> 8) yet superior FTIR ratios (RQ, R1 - R3) and stronger antioxidant activity; mid-power MWD (120 - 250 W) was detrimental. The colorimetric - spectroscopic linkages were found to be quantitative, with ΔE-IC50 exhibiting a weak-moderate relationship, and a* demonstrating a strong colleration with RQ (R2 ≈ 0.73). Chemometrics (PLSR with VIP) identified RQ/R3 as dominant predictors (R2{LOOCV} ≈ 0.33), thereby converting FTIR from descriptive readout to an actionable inline/at-line QC. Collectively, these results establish a predictive quality-control framework - using ΔE and a* with RQ - for efficient selection, development, and implementation of tropical herbal drying technologies, and provide actionable set-points (optimal: MWD 380 W; convective alternative: CTD 60 °C) that balance speed and bioactive retention.