Spouted Bed Drying of Fresh Papaya Seeds (Carica papaya L.): Hydrodynamic Behavior and Statistical Analysis

The processing of papaya (Carica papaya L.) generates substantial volumes of bioactive-rich seed residues that require efficient drying to prevent degradation. However, the hydrodynamic behavior of fresh seeds, characterized by high surface moisture and mucilaginous adhesion, remains poorly documented under spouted bed conditions. This study systematically investigated the drying performance of papaya seeds using a Box-Behnken experimental design. Initial trials showed that removing the sarcotesta drastically reduced the minimum spouting velocity (u _ms ) from 1.94 to 0.98 ms^-1 and the peak pressure dropped from 1200 to 490 Pa, highlighting the dominant role of surface cohesion. A 15 min flash-drying pretreatment at 4 m³ min^-1 was essential to reduce surface stickiness and enable stable spouting. The experimental design evaluated air temperature (40-60 °C), processing time (20-60 min), and airflow rate (1.0-2.0 m³ min^-1). Quadratic regression models for moisture content and water activity (a _w ) exhibited excellent fit (R ² > 0.99; R _adj ² > 0.97) with no significant lack of fit (p > 0.05). Multiresponse optimization via desirability profile (≈60 °C, ≈60 min, and 1.61 m³ min^-1) converged with experimental results (U = 7.2% and a _w = 0.57), reaching the thermodynamic safety threshold (a _w < 0.60) for microbial inhibition. These findings demonstrate the potential of spouted bed technology for the scalable and sustainable valorization of sticky agro-industrial residues, ensuring material stability for future bioactive compound extraction.