Impact of Microwave Power and Peeling on Drying Kinetics, Mathematical Modeling, Curcumin Retention, Microbial Safety, Texture, and Structural Integrity of Turmeric ( Curcuma longa

ABSTRACT

Turmeric ( Curcuma longa ) rhizomes are rich in bioactive phytochemicals and curcuminoids, especially curcumin, whose retention is strongly influenced by drying conditions. Although microwave drying has been widely investigated for turmeric, the influence of peel removal on microwave drying kinetics, quality retention, and structural characteristics remains poorly understood. Therefore, this study evaluated the effects of peeling, microwave drying (270–450 W), and hot air drying on drying behavior and quality characteristics of turmeric slices. Nine thin‐layer drying models were evaluated, with the Logarithmic model showing the best fit ( R ²  = 0.9995, RMSE = 0.0059). Microwave drying at 450 W achieved the shortest drying time (16 min) for peeled slices and yielded higher effective moisture diffusivity (2.1447 × 10 ⁻⁷  m ² /s), total phenolic content (63.09 mg GAE/g), total flavonoid content (36.50 mg QE/g), antioxidant activity (DPPH: 67.83%, FRAP: 11.84 mg QE/g), and curcumin content (2.47%), and resulted in significant microbial reduction (2.367 log CFU/g). Confocal laser scanning microscopy supported the findings for curcumin content. Scanning electron microscopy revealed that greater shrinkage occurred at 450 W, while hot air drying caused the most severe microstructural damage. Infrared spectra confirmed the presence of curcuminoids and polysaccharides bands with minimal structural alteration. Texture analysis showed better hardness in microwave‐dried slices, and peeled samples exhibited higher enthalpy. These findings highlight that microwave drying with peel removal effectively preserved phytochemicals, structural, and functional qualities, and stability of bioactive constituents in turmeric, ensuring efficient and sustainable spice processing.