Optimizing Anthocyanin Extraction from Juçara Pulp

The central composite rotatable design (CCRD) is a response surface methodology, in which a multivariate statistical tool is applied herein to optimize the extraction conditions of anthocyanins from juçara pulps. The relationship between the response and the independent variables was described according to the following polynomial equation: $$y={\beta }_0+{{\displaystyle \sum }}_{i=1}^k{\beta }_i{X}_i+{{\displaystyle \sum }}_{i=1}^k{\beta }_{ii}{X}_i{}^2+{{\displaystyle \sum }}_{i<j}^k{\beta }_{ij}{X}_i{X}_j$$
where β₀ represents the intercept or regression coefficient, β_i, β_ii, and β_ij are the linear, quadratic, and interaction coefficients, respectively, X_iand X_j are the independent variables, and k is the number of variables studied that can influence the response y. In this work, the independent variables were subjected to factorial planning of 2³ (3 variables, and 2 levels) to optimize the yield of extraction of anthocyanins (mg_anthocyanins·mL⁻¹) as the measured response function. Nineteen experiments were performed, including five replicates at the central point. A 90% confidence level was chosen to analyze the results. To verify the significance of the model parameters, the analysis of variance (ANOVA) was implemented. The coefficient of determination (R²) and adequate precision (F calculated value and p-value) were used to evaluate the adequacy of the polynomial equation for the response and optimum values. The experimental design, statistical analysis, and regression model were accomplished using Statistica version 13.5.0.17.
In this work, two factorial plannings were executed for both techniques of extraction, PLE and UAE. The first factorial planning was applied for PLE, in which the chosen levels of the independent variables were temperature (60, 80, and 100 °C), 1,2-propanediol concentration in water (15, 30, and 45 wt%), and pH (3.0, 4.5, and 6.0). The second factorial planning was carried out for UAE, in which amplitude (18, 30, and 42%), 1.2-propanediol concentration in water (15, 30, and 45 wt%), and pH (4.0, 7.0, and 10.0) were varied. All coded levels of independent variables used in the factorial planning for the optimization of operating conditions for both PLE and UAE was given in detail in Section 2.1 and Section 2.2, respectively. For both extraction methodologies, the pH of the solutions was adjusted from 0.1 M solutions of HCl or NaOH.