Effects of Infrared, Hot Air and Infrared‐Assisted Hot Air‐Drying on Drying Characteristics, Quality, and Energy Efficiency of Turmeric Slices

Abstract

The market value of turmeric is influenced strongly by volatile compounds which indicate product quality. In this study, turmeric slices of 5 mm with bed thicknesses of 50 mm were dried using three techniques: infrared (IR‐D), hot air (HA‐D), and infrared‐assisted hot air‐drying (IR‐HA‐D) at temperatures of 50°, 60°, and 70°C. This study examined the effects of increased bed thickness on drying kinetics, energy requirements, CO 2 emissions, and quality attributes under settings that more closely resemble industrial‐scale drying operations, in contrast to earlier studies that used a 25 mm bed thickness. Among the evaluated drying methods, IR‐HA‐D at 70°C exhibited the highest process efficiency, whereas IR‐HA‐D at 60°C provided superior retention of quality attributes, including curcumin, oleoresin, starch, and color. Seven thin‐layer drying models using nonlinear regression analysis were evaluated, with the Page model showing the best fit across all experimental conditions. The IR‐HA‐D method provided the highest retention of curcumin, oleoresin, starch and color value at 60°C, compared to both IR‐D and HA‐D. Statistical analysis confirmed that both drying techniques and temperature significantly influenced the quality characteristics of the dried turmeric ( p  < 0.01). Effective moisture diffusivity ranged from 7.61 × 10 −11 to 2.53 × 10 −10  m 2  s −1 while the activation energy required for moisture diffusion was 31.88 kJ mol −1 for IR‐D, 45.13 kJ mol −1 for HA‐D, and 32.11 kJ mol −1 for IR‐HA‐D.