Drying turmeric ( Curcuma longa L.) using far‐Infrared radiation: Drying characteristics and process optimization

Abstract This study investigated the turmeric drying characteristics and process parameters optimization for far‐infrared (FIR) radiation drying of turmeric. The initial moisture contents of the sliced wet turmeric samples were approximately 80 ± 0.12% (wb). The turmeric was exposed to 6.65, 5.97, 4.97, and 4.80 μm FIR radiation for 70, 30, 25, and 20 min, respectively. The moisture content and color (L*, a*, and b* values) of turmeric were measured during the experiment. The optimization experiments were conducted based on response surface methodology according to a central composite design with two independent variables: exposure time and FIR wavelength. The dependent variables considered were moisture content, curcumin content, energy consumption, and color‐changing index. The final moisture content and curcumin content were reduced with decreasing FIR radiation wavelength. FIR radiation drying of turmeric was observed to be a falling rate process. The optimal conditions were obtained with the FIR wavelength of 5.51 μm and exposure time of 21 min by applying the desirability function method. Under the optimal conditions, the predicted values of response variables, curcumin content, color‐changing index, energy consumption, and final moisture content were 3.26% (dry weight), 13.29, 2.51 kWh/g water, and 10.25% (wb). The desirability of 0.8157 under the optimal conditions further confirmed the validation of models. The results concluded that the FIR radiation could effectively apply for drying turmeric. Practical Applications The far‐infrared radiation can be applied for turmeric drying on an industrial scale. The drying rates and color‐changing index of turmeric increased with decreasing far‐infrared wavelength and increasing far‐infrared exposure time. Curcumin was reduced by increasing the far‐infrared wavelength and far‐infrared exposure time. The wavelength of 5.51 μm and exposure time of 21 min was the optimal conditions for FIR drying of turmeric. Therefore, the industry can achieve the optimum quality of turmeric within a shorter period of time by applying this technique.