2.3. Optimization of drying parameters

The factorial method deals with a problem of seeking the optimal conditions of the experiment, i.e., the most desirable. The optimal custom (2FI) design for three variables, i.e., samples (S₁ and S₂), microwave power (180, 360, 540, 720, and 900 W), and thickness of bed (2, 4, and 6 mm), including 22 trials formed with 3 replications, was used. This design was selected as it fulfilled most of the requirements needed for optimization of the drying conditions. The experimental design of independent parameters and layout are presented in Table 1 for these three variables, in which there are two levels of sample, five levels of microwave power, and three levels of drying bed thickness under the factorial design.

The goals for factors and responses were carefully selected. For factors, the options included maximizing, minimizing, targeting, keeping within a specified range, or having no specific goal (only applicable to responses). All independent factors (D and T) were maintained within their designated ranges. The responses, including water activity, Del E, and drying time, were minimized, while maximizing for ascorbic acid and overall acceptability. Additionally, the color B value and acidity of all samples were controlled to remain within the desired ranges.