Effect of Peeling, Moderate Power Microwave, and Hot Air Drying on Quality and Drying Characteristics of Turmeric (Curcuma longa L.)

Abstract

Objective: This study was conducted to evaluate the quality attributes of turmeric (Curcuma longa L.) rhizomes as influenced by peeling and moderate power microwave and hot air drying techniques. Methodology: Turmeric rhizomes (Kandhamal variety) were thoroughly cleaned, peeled, and sliced to a thickness of 3 mm, followed by drying using microwave power settings of 270-450 W and hot air drying at 60°C. The dried slices were ground, sieved (100 mesh), and stored for subsequent analysis. Quality evaluations included texture, physicochemical properties, microbial load, functional group analysis (FTIR), color parameters, and surface morphology (SEM). Results and Conclusions: Among the various conditions, turmeric dried at 450 W microwave power under peeled conditions exhibited superior quality retention, with the highest TPC (63.09 mg GAE/g), TFC (36.50 mg QE/g), and antioxidant activities (DPPH: 67.82% and FRAP: 11.83 mg QE/g), microbial reduction (2.367 log CFU/g), as well as improved color characteristics. Peeled samples consistently outperformed unpeeled ones in both drying methods, indicating more efficient preservation of phenolics and faster moisture removal. FTIR confirmed the presence of bioactive compounds, characterized by peaks at 3349, 2919, and 1612 cm-1. SEM illustrated significantly more shrinkage and microstructural changes at 450 W power. Hot air drying resulted in the lowest TPC (44.19 mg GAE/g) and TFC (24.74 mg QE/g) values, supporting that microwave drying is more effective at preserving bioactives due to its rapid drying and reduced thermal degradation.