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

• Optimization of microwave drying parameters to enhance the physicochemical quality of Averrhoa carambola . • Microwave drying significantly reduced the drying time of Averrhoa carambola . • Pretreatments enhanced color retention and reduced water activity. 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.