Comparative Analysis of Hot Air, Infrared, and Combined Drying on the Kinetic Properties, Color, and Rehydration of Orange and Black Carrots

In this study, the effect of hot air drying (HAD, 55 °C), infrared drying (IRD, 62 W), and combined infrared and hot air drying (CD) with different IR pretreatment times (30, 60, 90 min) on the drying kinetics, color, and rehydration of orange and black carrots was evaluated. IRD was characterized by the shortest drying time (140–160 min) and the highest effective moisture diffusion coefficient (1.40–1.42 × 10⁻⁹ m²/s), shortening the total drying time by 65–70% compared to HAD. The combined drying method (CD-90) with a 90-min IR pretreatment showed the best performance in terms of color retention (ΔE = 3.60–4.80) and rehydration rate (5.07–5.19), while achieving diffusion rates comparable to IRD. The Midilli-Küçük model described the drying kinetics of carrots with high accuracy for all drying methods (R² ≥ 0.9998). The results also indicated carrot variety-specific differences, with black carrots exhibiting faster moisture diffusion and higher structural strength. Results obtained in this study have shown that infrared-hot air combined drying, especially with extended infrared pretreatment of 90 minutes, is an energy-efficient and industrially applicable way to produce high-quality dried carrots capable of maintaining rehydration capacity and color retention capability.