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Bioethanol production from steam-pretreated corn stover through an isomerase mediated process

Paper ID Volume ID Publish Year Pages File Format Full-Text
33028 44953 2014 11 PDF Available
Title
Bioethanol production from steam-pretreated corn stover through an isomerase mediated process
Abstract

•A multi-step process consisting in hydrolysis, isomerisation, and cofermentation was investigated for the production of ethanol from corn stover steam pretreated.•The selected set-up determined a certain simultaneity of isomerisation and fermentation during the conversion of the hemicellulose hydrolysates.•Isomerase enzymes were inhibited by co-products generated during the fermentation of the entire slurry after the pretreatment.•The xylulose uptake during the fermentation with concentrated inocula of native S. cerevisiae was more effective in mixed hydrolysates with significant levels of glucose.

Agricultural by-products such as corn stover are considered strategic raw materials for the production of second-generation bioethanol from renewable and non-food sources. This paper describes the conversion of steam-pretreated corn stover to ethanol utilising a multi-step process including enzymatic hydrolysis, isomerisation, and fermentation of mixed hydrolysates with native Saccharomyces cerevisiae. An immobilised isomerase enzyme was used for the xylose isomerisation along with high concentrations of S. cerevisiae. The objective was to assess the extent of simultaneity of the various conversion steps, through a detailed analysis of process time courses, and to test this process scheme for the conversion of lignocellulosic hydrolysates containing several inhibitors of the isomerase enzyme (e.g. metal ions, xylitol and glycerol).The process was tested on two types of hydrolysate after acid-catalysed steam pretreatment: (a) the water soluble fraction (WSF) in which xylose was the largest carbon source and (b) the entire slurry, containing both cellulose and hemicellulose carbohydrates, in which glucose predominated.The results indicated that the ethanol concentration rose when the inoculum concentration was increased in the range 10–75 g/L. However, when xylose was the largest carbon source, the metabolic yields were higher than 0.51 gethanol/gconsumed sugars probably due to the use of yeast internal cellular resources. This phenomenon was not observed in the fermentation of mixed hydrolysates obtained from the entire pretreated product and in which glucose was the largest carbon source. The ethanol yield from biomass suspensions with dry matter (DM) concentrations of 11–12% (w/v) was 70% based on total sugars (glucose, xylose, galactose). The results suggest that xylulose uptake was more effective in mixed hydrolysates containing glucose levels similar to, or higher than, xylose.Analysis of the factors that limit isomerase activity in lignocellulosic hydrolysates excluded any inhibition due to residual calcium ions after the detoxification of the hemicellulose hydrolysates with Ca(OH)2. By contrast, most of the enzyme activity ceased during the fermentation of the entire slurry after steam explosion, probably due to synergistic inhibition effects of various fermentation co-products.

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Bioethanol production from steam-pretreated corn stover through an isomerase mediated process
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Publisher
Database: Elsevier - ScienceDirect
Journal: New Biotechnology - Volume 31, Issue 2, 25 March 2014, Pages 185–195
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us