Exploring laccase and mediators behavior during saccharification and fermentation of steam-exploded wheat straw for bioethanol production

BACKGROUND: Laccases represent a very powerful tool to improve biorefining processes from lignocellulosic feedstocks. These enzymes are being investigated not only for potential use as pretreatment agents in bioethanol production, mainly as a delignifying agent, but also as a biotechnological tool for removal of inhibitors (mainly phenols) of subsequent fermentation processes. RESULTS: In this work, the treatment of the water insoluble solids (WIS) fraction from steam-exploded wheat straw with Pycnoporus cinnabarinus laccase and different laccase-mediator systems (LMS) did not decrease the lignin content, resulting in lower glucose recoveries during the subsequent saccharification. In combination with an alkaline extraction, the treatment with laccase/LMS produced no synergistic effect enhancing the delignification or saccharification of WIS. In contrast, laccase reduced the soluble phenols (95% of the total phenols identified) of the whole slurry from steam-exploded wheat straw, improving the yeast performance during the fermentation and enhancing the ethanol yields. CONCLUSIONS: The efficiency of P. cinnabarinus laccase with or without mediators as a delignifying agent on steam-exploded wheat straw for bioethanol production was not observed, whereas its detoxification ability was shown. Thus, new laccases or designing laccases with ability to delignify and detoxify simultaneously needs to be explored in order to produce major ethanol global yields. (C) 2015 Society of Chemical Industry