“Instant Controlled Pressure Drop” as a Pretreatment Bioprocess for Drying of Tunisian Arbutus unedo L. Leaves: Kinetic Analysis and Phenomenological Modeling by Starting Accessibility and Effective Water Diffusivity

Instant controlled pressure drop (DIC) pretreatment followed by airflow drying was investigated for Arbutus unedo L. leaves from four Tunisian proveniences. A two-factor central composite design examined saturated steam pressure and treatment time. Drying kinetics were analyzed using an infinite-plate diffusion model to determine effective diffusivity (Deff) and starting accessibility (δWs). For the DIC 9 treatments presented, the time required to reach a common moisture content was 29.9–56.8% shorter than for the corresponding mean untreated curves. Increased effective diffusivity was not consistently accompanied by increased signed starting accessibility, suggesting that faster moisture transport during the main drying stage did not necessarily translate into improved initial drying behavior, as characterized by the extrapolated descriptor. Signed δWs was derived by extrapolating the main drying stage back to its initial time; it therefore characterized the relationship between initial moisture content and the subsequent drying trajectory. Statistical analyses yielded empirical models describing the linear, quadratic and interaction effects of swell-drying processing parameters on the measured responses. The VAR 3 starting-accessibility model showed the strongest cross-validation support. These findings highlight the importance of selecting suitable pressure–time combinations for each provenience to improve pretreatment performance and the complementary value of phenomenological and response-surface modeling in guiding this selection.