Optimization of drying conditions for microwave-vacuum drying of tomato snack bars using response surface methodology

The study focused on optimizing microwave-vacuum drying (MVD) for tomato snack bars using response surface methodology (RSM). Key variables included drying time, microwave power, and absolute chamber pressure, with a Box-Behnken design testing power levels (1.0, 1.2, 1.4 kW), pressures (0.2, 0.35, 0.5 bar), and drying times (8, 10, 12 min). Targets for water activity (0.50), moisture content (15%), and hardness (45 N) were set based on comparable studies in snack bar literature. The goal was to maximize lycopene and redness, indicated by the a ^⁎/b ^⁎ value, whereas energy demand was calculated as a deterministic objective. The optimal parameters were identified as 1.28 kW power, 0.46 bar pressure, and 9.2 min drying time, achieving a desirability of 0.83. At the selected condition, the experimental values were water activity (0.494), moisture content (15.15%), lycopene (216.5 mg/kg), redness (a ^⁎/b ^⁎) of 0.806, hardness (54.35 N), and the corresponding theoretical energy estimate was 1424 kJ.