Drying Kinetics, Thermodynamic Properties and Volatile Preservation of Coffee Husks from Organic and Conventional Production Systems

Coffee husks (Coffea arabica) are abundant agro-industrial by-products with potential for value-added applications, making the optimization of drying conditions essential for preserving their quality. This study evaluated the effects of drying temperature on the drying kinetics, thermodynamic properties, and volatile profile of coffee husks from organic and conventional production systems. Samples were dried in a convective fixed-bed dryer at 30, 40, and 50 °C. Drying kinetics were described using fifteen mathematical models, while thermodynamic parameters (ΔH, ΔS, and ΔG), volatile compounds (HS-SPME/GC–MS), water activity (Aw), and texture were evaluated. The Modified Henderson and Pabis model provided the best fit to the drying data (R2 > 0.99). A total of 505 volatile compounds were identified, and samples dried at 40 °C retained the highest number of sensory-relevant compounds. Organic coffee husks exhibited a distinct volatile profile compared with conventional husks, possibly due to differences in postharvest processing. Drying reduced water activity to values below 0.60, which are generally considered unfavorable for the growth of most microorganisms during storage. Overall, the results suggest that drying at 40 °C provides a suitable balance between drying performance and volatile compound preservation in coffee husks.