Convective Drying of Avocado Seeds: Mass Transfer Thermodynamics and Multi-Response Optimization of Functional and Phytochemical Properties

Avocado seeds represent an underutilized agro-industrial by-product rich in dietary fiber and bioactive compounds. This study evaluated the impact of convective drying (45–75 °C, 3–9 mm thickness, 0.5–2.5 m s−1 air velocity) on the mass transfer kinetics, techno-functional properties, and phytochemical stability of the seed matrix. The Midilli model accurately described dehydration kinetics, with effective diffusivities around 10−9 m2 s−1. Principal Component Analysis of the evaluated parameters revealed trade-offs between drying efficiency and phytochemical preservation. While the lignocellulosic fiber matrix remained relatively stable, preserving its hydration and oil retention capacities independently of thermal severity, prolonged processing times resulted in lower phenolic acid content and promoted non-enzymatic browning. Crucially, high air velocities were associated with higher retention of thermolabile bioactives, potentially due to accelerated moisture removal and shorter cumulative thermal exposure. A multi-response desirability approach established three optimized processing scenarios, yielding a phytochemical-rich concentrate (45 °C, 3 mm, 2.5 m s−1), a highly soluble ingredient (75 °C, 8.7 mm, 0.5 m s−1), and a water-retaining bulking matrix (75 °C, 7.4 mm, 0.5 m s−1). These findings demonstrate that convective drying thermodynamics can be strategically modulated to tailor avocado seed waste into specialized functional ingredients for the circular bioeconomy.