Fermentation of the Straw Material Paja Brava by the Yeast &amp;lt;i&amp;gt;Pichia stipitis&amp;lt;/i&amp;gt; in a Simultaneous Saccharification and Fermentation Process

Cristhian Carrasco,Mats Galbe,Henrique Baudel,Gunnar Lidén,Christian Roslander

doi:10.4236/jsbs.2013.32014

Abstract

Paja Brava is a native South American grass with a high carbohydrate content. In the current work, the potential of using this feedstock for ethanol production using a simultaneous saccharification and fermentation (SSF) process with the xylose-fermenting yeast Pichia stipitis (Scheffersomyces stipitis) CBS6054 was investigated. The straw material was subjected to SO2 catalyzed steam pretreatment at 200°C and 5 min residence time, which resulted in a solubilization of pentose sugars (mainly xylose) of 64% with only minor amounts of degradation products. The obtained material, including the pretreatment liquid, was subsequently hydrolyzed and fermented in an SSF process at microaerobic conditions using either a batch or a fed-batch process at a total water-insoluble solids loading of 10%. Overall yields of ethanol based on all available sugars of 0.24 g/g and 0.27 g/g were obtained for batch and fed-batch mode of operation, respectively. The higher yield in the fed-batch process coincided with a higher degree of conversion of the sugars in the liquid medium, in particular of arabinose, for which the conversion was doubled (from 48% to 97%).

Highlights

Paja Brava, a Gramineae material, is the most common native grass species on the Bolivian Altiplano and is widely distributed in South America in general [1]
Xylose was found to be the completely dominant sugar in the liquid fraction after steam pretreatment, followed by arabinose, whereas only relatively low amounts of glucose and cellobiose were found in the liquid fraction
In the anaerobic fermentation tests, the extent of inhibition was tested by comparing to fermentation of a synthetic medium with the same sugar concentration as the hydrolysate

Summary

Introduction

Paja Brava, a Gramineae material, is the most common native grass species on the Bolivian Altiplano and is widely distributed in South America in general [1]. In this straw, D-xylose is the most predominant hemicellulosic sugar, constituting up to 25% of the total dry weight, which is similar to straw materials such as wheat straw or sugarcane bagasse [2,3]. Principal options for ethanol production from lignocellulosics by the biological route include enzymatic hydrolysis followed by fermentation— Separate Hydrolysis and Fermentation, SHF—or Simultaneous Saccharification and Fermentation, SSF The latter may include conversion of both conversion of C5 and C6 sugars, in which case the term simultaneous saccharification and co-fermentation, SSCF, is used [5].

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Conclusion