Effect of Spray Drying Conditions on the Physicochemical, Thermal, and Microstructural Properties of Coffee Mucilage Powder (Coffea arabica - Castillo)

Juan David Rivera Escobar^1,2*JOSE HOYOS¹Diego Fernando Roa-Acosta¹Jhan Carlos Delgado¹Victor Hugo Rosero¹Gerardo Andres Torres¹

• ¹University of Cauca, Popayán, Colombia
• ²Universidad Icesi, Cali, Colombia

This study evaluated the effects of different spray drying (SD) conditions on the physicochemical, thermal and microstructural properties of coffee mucilage powder (CMP). The mucilage was obtained through enzymatic hydrolysis using pectinases, which broke down the mucilage structure by hydrolyzing α-1,4 glycosidic bonds. A central composite rotatable design was used to assess the effects of inlet air temperature (115.85 °C to 144.14 °C) and feed flow (0.23 L/h to 0.66 L/h) on the response variables. Results showed that SD conditions significantly impacted phenolic content and antioxidant capacity. Increased temperature led to a significant rise in both phenolic content and antioxidant activity, with temperature being a more influential factor than feed flow. Lower feed flow resulted in smaller droplet sizes, which enhanced dehydration efficiency and preserved higher phenolic content. The phenolic content ranged from 135.53 mg GAE/100 g to 165.88 mg GAE/100 g, and antioxidant capacity measured by FRAP, ABTS, and DPPH assays followed similar trends. The glass transition temperature (Tg) of CMP was measured by differential scanning calorimetry (DSC), with values ranging from 61.09 °C to 62.18 °C, showing no significant differences among treatments. Particle size and morphology analysis using scanning electron microscopy (SEM) showed that particles were mostly spherical with corrugated surfaces, with particle size ranging from 14.93 µm² to 22.03 µm². Higher feed flow resulted in larger particles, while higher temperatures produced smaller particles. The study also assessed CMP stability in aqueous solutions at different pH values by measuring Zeta potential (PZ) and hydrodynamic particle diameter (HPD) across a pH range of 3.0 to 9.0. Additionally, water absorption isotherms were constructed using the BET and GAB models, showing high hygroscopicity. Temperature significantly affected the monolayer moisture content (Xm) and absorption energy (C), indicating reduced affinity for water at higher temperatures. This study provides insights into SD conditions to preserve the bioactive properties of coffee mucilage, improving the thermal stability and microstructure of CMP, making it a valuable ingredient for food formulations and coffee byproduct valorization.