Optimization of pretreatment conditions of fig (Ficus carica) using autoclave and microwave treatments

This study compares the optimization of microwave-assisted (MW) and steam-assisted autoclave (AC) pretreatments of fig ( Ficus carica ) to produce fermentable sugar. The central composite design response surface method was used for the optimization of process parameters. The independent variables for MW were particle diameter of dried fig (D p = 200–375 µm), pH (3.00–5.00), and power (P = 250–670 W); the variables for AC were particle diameter (D p = 200–375 µm), pH (3.00–5.00), temperature (T = 95–120 °C), and time (t = 30–50 min). The dependent variable was total sugar concentration (TSC) upon hydrolysis. Statistical analysis of the observed TSC indicated that all MW pretreatment parameters were significant. However, the temperature was the only significant parameter affecting fig hydrolysis in AC. Regression coefficients between observed and predicted values were in good agreement for AC ( R 2 = 0.90) and MW ( R 2 = 0.88) indicating model strength to the experimental data. The sum of ranking method (SRM) was done to test the similarity of observed and predicted TSC within the studied ranges of the independent variables. The optimum conditions for maximum sugar concentration by MW were determined as D p = 370.72 µm, pH 4.96, and P = 253.67 W with TSC = 82.9 g/L. AC conditions were D p = 263.19 µm, pH = 3.02, T = 120 °C, and t = 30.00 min with maximum sugar concentration of 70.0 g/L. A validation experiment was also conducted on MW and AC models and a good agreement between model prediction and observed responses was observed. This study demonstrated the effectiveness of MW and AC as potential pretreatment options for fig hydrolysis to yield the high sugar concentration that can be used as a substrate for biofuel production. Graphical abstract