Maximising the Benefits of Enzyme Synergy in the Simultaneous Saccharification and Fermentation of Jerusalem Artichoke (Helianthus tuberosus) Tuber Residues into Ethanol

Purpose An integrated approach for the co-production of food, feed and biofuel has the potential maximise the economic value from Jerusalem artichoke (JA). A biorefinery approach was used for extracting protein and inulin from JA tubers, and producing ethanol from the extraction residues using an optimised cocktail of enzymes. Method Inulin and protein products were pre-extracted from tubers, resulting in tuber residues with unextracted inulin (38%) and lignocellulosic fibres (25%). Fed-batch fermentation was used for ethanol production from the residues, using a mixture design, to optimize the cocktail of exo- and endoinulinase, Cellic® CTec3 and Pectinex Ultra-SP, to minimise the total enzyme dosage and maximise the sugar conversion and ethanol yields during simultaneous saccharification and fermentation of the residues, by exploiting synergistic action among enzymes in the cocktail. Results High gravity fermentation of the residues with 21% w/v solids loading, resulted in an ethanol concentration and yield of 38 g/L and 83% of the theoretical max, respectively, and a combined inulin and cellulose conversion yield of 74%. Synergistic co-operation among the enzymes improved the hydrolysis of inulin and LCFs. The enzyme cocktail demonstrated a degree of synergy that resulted in the highest sugar yield of 0.74 g/g sugars compared to yields in the range of 0.10–0.39 g/g sugars for individual enzymes. The xylose and glucan recovery yield for this optimised cocktail was 62 and 66%, respectively. Ethanol yields were improved from 37%, when using individual enzymes, to 83%, when using the enzyme cocktail. Conclusions Synergistic co-operation among the hydrolytic enzymes significantly improved the saccharification and fermentation efficiency of the tuber residues, in part due to optimisation of the composition of the enzyme cocktail preparation. The optimised cocktail resulted in substantial LCFs conversion without the pre-treatment of the tuber residues. Graphic Abstract