Optimization and modeling of microwave drying of osmotic dehydrated Averrhoa carambola: physicochemical and dielectric characterization

The objective of this research was to optimize the microwave dehydration process of blanched and osmotic dehydrated carambola (starfruits) slices to minimize moisture content (%), water activity (a_w), and maximize lightness (L*) and effective diffusivity (D_eff). Microwave drying of 0.5 mm slices was evaluated using a 2^K response surface design, considering blanching time (10–30 s), sucrose concentration (50–60 °Brix), and drying power (480–840 W) as factors. Physicochemical and dielectric properties of carambola slices were characterized in three stages: fresh, blanched – osmotic dehydrated, and blanched – osmotic dehydrated - microwave dried. Drying kinetics were analyzed with models including Lewis, Page, Modified Page, Logarithmic, Wang and Singh, Peleg, and Henderson-Pabis. Subsequently, moisture content (%), a_w, L*, and D_eff were optimized. Results showed significant modifications in physicochemical and dielectric properties after pretreatments and microwave drying. The logarithmic model provided the best fit to drying curves, with R² = 0.9995 and SSE = 0.0001. Optimal drying conditions were identified at 10 s blanching, 50 °Brix sucrose, and 840 W power, achieving a global desirability of 0.62. Under these conditions, the final product exhibited: moisture content = 7.50%, a_w = 0.56, L* = 44.99, and D_eff = 1.94×10⁻⁶ m²/s. These findings demonstrate the potential of integrating blanching, osmotic dehydration, and microwave drying to improve the quality of dried carambola slices, supporting the development of efficient, sustainable, and high-quality dehydration processes.