Infrared-Assisted Hot Air Drying of Turmeric Slices: Effects on Drying Kinetics, Quality, Efficiency, Energy Considerations, and Mathematical Modeling

Abstract

The commercial value of turmeric is significantly influenced by the percentage of volatile compounds. Drying techniques reported in previous studies for turmeric showed a reduction in volatile compounds, which negatively affected the quality and market value. In this investigation, drying trials were conducted on turmeric slices with bed thicknesses ranging from 10–25 and 10–50 mm using infrared drying, hot air drying (HAD), and infrared-assisted hot air drying (IR-HAD) methods at temperatures of 50°C, 60°C, and 70°C. The air velocity was maintained at 2 m/s, with an infrared radiation intensity of 3.02 W/cm². The results indicated that IR-HAD at 70°C with a bed thickness of 25 mm achieved the best outcomes in terms of drying rate, efficiency, specific energy consumption, and CO₂ emissions. Conversely, IR-HAD at 60°C with a bed thickness of 25 mm was optimal for retaining quality parameters, such as curcumin, oleoresin, color, and starch content. Notably, the drying time at 70°C for the 10–25-mm bed thickness was 54.54% shorter compared with 50°C for IR-HAD. Statistical analysis revealed significant effects (p < 0.01) of drying techniques, bed thickness, and drying temperatures on quality parameters. IR-HAD at 60°C with a bed thickness of 25 mm emerged as the preferred operating condition for producing high-quality turmeric. Nonlinear regression analysis confirmed the suitability of seven different thin-layer drying models, with the page model being the most accurate predictor of turmeric slice drying under varied conditions. IR-HAD demonstrated its potential to accelerate the drying rate during the initial stage of the process, with reduced thickness proving more effective due to the increased surface area facilitating faster moisture removal. IR-HAD at 60°C retains the maximum percent of volatile compounds and maintains the quality by faster and uniform drying. Therefore, employing IR-HAD offers a more energy-efficient sustainable method while ensuring quality retention in dried turmeric slices.