Fed-Batch Saccharification as a Strategy towards Reducing Enzyme Dosage and Enhancing Fermentable Sugar Yield from Pretreated Lignocellulo-Starch Biomass

Abstract

Lignocellulo-starch biomass (LCSB) comprising root and vegetable processing residues contain starch also along with cellulose and hemicellulose and hence require whole slurry saccharification using an enzyme cocktail containing starch hydrolysing enzyme as well along with cellulase and xylanase. The cost-effective production of ethanol necessitates high fermentable sugar yield (> 80 g/l) in the hydrolysate which is possible through fed-batch saccharification as it overcomes issues such as low mass transfer and high viscosity of slurry encountered on high solids loading. To our knowledge no information is available on the fed-batch saccharification of LCSBs and hence the objective of the study was to investigate the possibility of enhancing the sugar yield at low enzyme dosage through fed-batch saccharification approach. Fed-batch saccharification of pretreated LCSBs [steam (ST), dilute sulphuric acid (DSA) and microwave-assisted DSA (MW-DSA)] in enhancing the sugar yield was investigated using a triple enzyme cocktail at two cumulative loading densities (15 g/100 ml and 20 g/100 ml) and compared with the respective batch system. The hydrolysis yield from ST fed-batch system was very high (84–95%) for the residues followed by 83–90% yield from MW-DSA system at 15 g/100 ml cumulative substrate loading. Glucose and xylose were uniformly present in all the hydrolysates with higher levels of glucose in the steam pretreated fed-batch system SFB1 (15 g/100 ml). High phenolic retention in the hydrolysates did not affect saccharification as detoxification chemicals were supplemented. Fed-batch saccharification enhanced the sugar yield from pretretated LCSBs and based on the hydrolysis yield, 15 g/100 ml cumulative substrate loading was better than 20 g/100 ml loading and steam pretreatment (45 min) emerged as the best. Pulsed addition of substrate with only one-time enzyme feeding at the start resulted in enzyme saving during the fed-batch saccharification.