Binary- and triple-enzyme cocktails and their application mode affect fermentable sugar release from pretreated lignocellulo-starch biomass

Lignocellulo-starch biomass (LCSB) comprising roots and vegetable processing wastes has high starch besides cellulose and hemicelluloses and warrants different pretreatment and saccharification approaches. The fermentable sugar yield from steam/dilute sulphuric acid (DSA)-pretreated biomass during saccharification with binary [cellulase + amylolytic enzyme (Stargen)] or triple (cellulase + xylanase + Stargen) enzyme cocktails was compared. The factors such as pH (5.0), temperature (50 °C) and enzyme dosage (16 FPU/g cellulose) for cellulase (Ecozyme RT80) action were optimized using response surface methodology. As pretreated liquor is rich in sugars, whole slurry saccharification was needed for LCSBs and saccharification efficiency (120 h) was significantly higher for steam-pretreated biomass with all application modes. Preferential hydrolysis of starch in steam-pretreated biomass by Stargen followed by cellulolysis was advantageous than the application sequence with cellulase followed by Stargen. Triple-enzyme-based saccharification of steam-pretreated biomass significantly enhanced the overall conversion efficiency (OCE; 85–98%) compared to only 28–49% in the native untreated biomass, while lower OCE was observed in the case of DSA-pretreated and saccharified biomass. Supplementation with both xylanase and Stargen pronouncedly enhanced the OCE for steam-pretreated biomass with only insignificant difference between the exposure periods, indicating the obligatory need for both enzymes for optimal saccharification of LCSBs.