Experimental optimization of enzymatic and thermochemical pretreatments of bread waste by central composite design study for bioethanol production

The present study aimed at optimizing the combined effect of enzymatic and thermo-chemical pretreatment hydrolysis of bread waste (BW) for enhancing the yield of reducing sugars (RS). Statistical optimization of enzymatic and thermochemical pretreatment processes was performed using the central composite design (CCD) tool of response surface methodology (RSM) using four process parameters (waste bread ratio, alpha-amylase concentration, temperature and pH) on total sugars yield as response variable. It was found that the optimal conditions for maximally RS yield were at bread ratio of 0.03 g/mL, alpha-amylase concentration of 0.2 mL/L, temperature of 100 °C and pH 5.3. Under these conditions, the yield of RS reached 90%, with bioethanol concentration of about 85.8 g/L after 72 h of batch fermentation. The modified Gompertz equation was used to describe the cumulative bioethanol production. A good agreement was found between simulated and experimental data.