Optimization of fluidized bed drying process parameters and quality evaluation of ready to use onion slices

This study investigates the kinetics and optimization of fluidized bed drying of onion slices using CCRD design by Response Surface Methodology, aiming to enhance drying efficiency and preserve product quality. The effects of drying process parameters viz., drying temperature (43.18, 50,60,70, & 76.82 °C), NaCl concentration (6.59, 10, 15, 20, & 23.41%) and bed thickness (1.636, 3,5, 7, & 8.362 mm) on dehydration ratio, rehydration ratio, color change, ascorbic acid content and overall acceptability were evaluated using multiple response optimization techniques. Optimization analysis revealed that a drying temperature of 70 °C, NaCl concentration of 20%, and bed thickness of 3 mm yielded the highest desirability value of 0.637. Under these optimized conditions, the dehydration ratio, rehydration ratio, color change, ascorbic acid content, and overall acceptability of onion slices were measured at 6.76, 5.87, 4.85, 8.06 and 4.02, respectively. Higher drying temperatures, NaCl concentrations and lower bed thickness were associated with faster drying rates. Various mathematical models, including Page, Logarithmic, Henderson and Pabis, Midilli and Newton models, were employed to characterize the drying kinetics, with the Page Model demonstrating superior fit to experimental data. Furthermore, quality parameters such as moisture content, water activity, ascorbic acid content, color change and crispiness of onion slices stored for three months under optimized conditions and packaged in different materials (LDPE and HDPE) were evaluated. Results indicate that the optimized fluidized bed drying process parameters effectively maintained the quality of onion slices during storage.