Ethanol from laccase-detoxified lignocellulose by the thermotolerant yeast Kluyveromyces marxianus – Effects of steam pretreatment conditions, process configurations and substrate loadings

Abstract

In our previous work, the ability of laccase enzymes to improve the fermentation performance of the thermotolerant yeast Kluyveromyces marxianus CECT 10875 on steam-exploded wheat straw slurry was demonstrated. As a continuation of this study, the present research evaluates different aspects, including pretreatment conditions, process configurations and substrate loadings, with the aim to proceed towards the use of K. marxianus and laccases for second generation ethanol production. For it, two wheat straw slurries resulting from different steam explosion pretreatment conditions (200 °C, 2.5 min and 220 °C, 2.5 min) were employed at various substrate loadings [5–14% (w/v)] under two process configurations: SSF (simultaneous saccharification and fermentation) and PSSF (presaccharification and simultaneous saccharification and fermentation). The better performance of K. marxianus was observed on the slurry produced at softer conditions. Its lower inhibitors content allowed to increase the total solids loading up to 10% (w/v) in both process configurations, reaching higher ethanol concentrations (12 g/L). Moreover, laccase detoxification improved these results, particularly in SSF processes, increasing the substrate loading up to 12% (w/v) and, consequently, obtaining the highest ethanol concentration (16.7 g/L).