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

Abstract

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. HIGHLIGHTS Drying methods (sun, room temperature, convective tray, and microwave) were proven to significantly determine the kinetics and bioactive quality of Annona muricata The Midilli model was proven to be the most accurate global predictor (R2 > 0.95; RMSE < 0.05). Meanwhile, the Jenna-Das model exhibited optimal performance within the confines of the convective subset. Microwave drying at 380 W accelerated the drying process by approximately 225 times compared to CTD 50 °C and maintained antioxidant activity approximately 5 times stronger than fresh leaves. A clear trade-off was identified: low ΔE (~2,7 at 40 °C CTD) maintained appearance but reduced phenolic content, while high intensity (60 °C CTD, 380 W MWD) caused color shift (ΔE > 8) but maintained better IC50 values and FTIR ratios. Colorimetric parameters (ΔE, a*) have been shown to strongly correlate with FTIR ratios and IC50, thus forming a rapid and non-destructive prediction framework for tropical herbal drying. GRAPHICAL ABSTRACT

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