Multi-objective optimization of bioethanol production during cold enzyme starch hydrolysis in very high gravity cassava mash

Cold enzymatic hydrolysis conditions for bioethanol production were optimized using multi-objective optimization. Response surface methodology was used to optimize the effects of α-amylase, glucoamylase, liquefaction temperature and liquefaction time on S. cerevisiae biomass, ethanol concentration and starch utilization ratio. The optimum hydrolysis conditions were: 224 IU/gstarch α-amylase, 694 IU/gstarch glucoamylase, 77 °C and 104 min for biomass; 264 IU/gstarch α-amylase, 392 IU/gstarch glucoamylase, 60 °C and 85 min for ethanol concentration; 214 IU/gstarch α-amylase, 398 IU/gstarch glucoamylase, 79 °C and 117 min for starch utilization ratio. The hydrolysis conditions were subsequently evaluated by multi-objectives optimization utilizing the weighted coefficient methods. The Pareto solutions for biomass (3.655–4.380 × 108 cells/ml), ethanol concentration (15.96–18.25 wt.%) and starch utilization ratio (92.50–94.64%) were obtained. The optimized conditions were shown to be feasible and reliable through verification tests. This kind of multi-objective optimization is of potential importance in industrial bioethanol production.