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Improvement in Ethanol Yield from Lignocellulo-Starch Biomass using Saccharomyces cerevisiae Alone or its Co-culture with Scheffersomyces stipitis

Author(s):

Mithra M.G and Padmaja G*   Pages 1 - 20 ( 20 )

Abstract:


Background: Although extensive studies have been carried out on ethanol production from LCBs by different saccharification and fermentation approaches, literature on lignocellulo-starch biomass (LCSB) such as peels of root and vegetable crops containing starch as a major polysaccharide besides cellulose and hemicellulose is scanty. Previous studies showed that fed batch separate hydrolysis and fermentation (F-SHF) was beneficial that fed batch simultaneous saccharification and fermentation (F-SSF) for these residues because of the higher requirement of enzymes and yeast in the former case than F-SHF to achieve the same ethanol yield.

Objective: This study aimed at further modification of the saccharification and fermentation strategies by including a prehydrolysis step prior to the SSF and compared the ethanol yields from pretreated processing residues with co-culture fermentation using two organisms such as Saccharomyces cerevisiae and Scheffersomyces stipitis.

Methods: Two strategies such as fed batch hybrid simultaneous saccharification and fermentation (F-HSSF) and fed batch separate hydrolysis and co-culture fermentation (F-SHCF) in improving ethanol yield from steam (ST) or dilute sulfuric acid (DSA) pretreated lignocellulo-starch biomass (peels of root and vegetable crops) was studied.

Results: There was a progressive build up of ethanol concomitant with RS production and utilization during F-HSSF up to 72 h and further ethanol production up to 120 h was negligible. The ethanol content did not differ significantly between steam (ST) and DSA pretreated residues under F-HSSF. Although very high RS consumption and ethanol production were obtained in the initial 24 h of fermentation of hydrolysates by Saccharomyces cerevisiae under the F-SHCF system, further increase during the next 24 h was negligible. Nevertheless a rapid hike in ethanol production was observed when Scheffersomyces stipitis was also supplemented to the fermentation system due to xylose conversion to ethanol.

Conclusion: While steam pretreatment gave higher ethanol yields (296-323 ml/kg) than DSA pretreatment under F-HSSF, the latter was advantageous under F-SHCF for certain residues. As prehydrolysis (24 h; 50 °C) enhanced initial sugar levels in the slurry favouring fast fermentation and subsequent saccharification and fermentation occurred concurrently at 37 °C for 120 h leading to energy saving, F-HSSF was beneficial for the selected residues. As the residues had only low hemicellulose content than the typical lignocellulosic biomass, the relative advantage of co-culture fermentation over monoculture fermentation was not significant.

Keywords:

Lignocellulo-starch biomass, Ethanol, Fed batch, Hybrid-SSF, Co-culture, F-SHF

Affiliation:

ICAR-Central Tuber Crops Research Institute, Division of Crop Utilization, ICAR-Central Tuber Crops Research Institute, Division of Crop Utilization



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