Impact of Skin Presence and Slice Thickness of Ripe Tomato (Solanum lycopersicum l.) on Microwave Drying Kinetics

Abstract

Background: Tomato is highly perishable because of its high moisture content, resulting in substantial post-harvest losses and a short shelf life. Microwave drying offers rapid volumetric heating, but its efficiency may be strongly influenced by fruit skin and slice thickness, which affect moisture transfer during drying. Aims: To quantitatively assess the influence of epicarp presence and slice thickness on the microwave drying kinetics of ripe tomato, with a view to reducing the substantial post-harvest losses affecting the tomato value chain in Côte d’Ivoire. Study Design:  A comparative experimental study was conducted on tomato half-portions with and without skin and on slices of three different thicknesses (5, 10 and 20 mm). Place and Duration of Study: Samples were procured in Yamoussoukro, Côte d’Ivoire, and the investigation was conducted between July and August 2026. Methodology: Fresh, ripe tomatoes (SODEFEL variety) were cut into half-portions (with and without skin) and into calibrated slices (5, 10 and 20 mm) and then dried in a microwave oven (400 W) until mass stabilisation. Water loss kinetics were monitored by periodic weighing, and effective moisture diffusivity was determined using Fick's second law. Results: Skin presence slowed initial water loss but promoted rapid internal pressure build-up followed by cracking and marked exudation; unpeeled samples dried more slowly (61 min) than peeled ones (17 min). Drying time increased with thickness (28, 33 and 43 min for 5, 10 and 20 mm, respectively). The apparent effective moisture diffusivity paradoxically increased with thickness, from 3.24 × 10⁻⁸ m². s⁻¹ (5 mm) to 1.19 × 10⁻⁷ m². s⁻¹ (10 mm) and 3.96 × 10⁻⁷ m². s⁻¹ (20 mm), reflecting a shift from a diffusional regime to a convective one. Conclusion: Skin condition and slice thickness affected microwave drying behaviour. Thinner slicing reduced drying time, while skin micro-perforation is proposed for further evaluation as a means of facilitating moisture removal while limiting exudation.