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Future biorefineries will integrate biomass conversion processes to produce fuels, power, heat and value-added chemicals. Due to its low price and wide distribution, lignocellulosic biomass is expected to play an important role toward this goal. Regarding renewable biofuel production, bioethanol from lignocellulosic feedstocks is considered the most feasible option for fossil fuels replacement since these raw materials do not compete with food or feed crops. In the overall process, lignin, the natural barrier of the lignocellulosic biomass, represents an important limiting factor in biomass digestibility. In order to reduce the recalcitrant structure of lignocellulose, biological pretreatments have been promoted as sustainable and environmentally friendly alternatives to traditional physico-chemical technologies, which are expensive and pollute the environment. These approaches include the use of diverse white-rot fungi and/or ligninolytic enzymes, which disrupt lignin polymers and facilitate the bioconversion of the sugar fraction into ethanol. As there is still no suitable biological pretreatment technology ready to scale up in an industrial context, white-rot fungi and/or ligninolytic enzymes have also been proposed to overcome, in a separated or in situ biodetoxification step, the effect of the inhibitors produced by non-biological pretreatments. The present work reviews the latest studies regarding the application of different microorganisms or enzymes as useful and environmentally friendly delignification and detoxification technologies for lignocellulosic biofuel production. This review also points out the main challenges and possible ways to make these technologies a reality for the bioethanol industry.

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Operating the saccharification and fermentation processes at high-substrate loadings is a key factor for making ethanol production from lignocellulosic biomass economically viable. However, increasing the substrate loading presents some disadvantages, including a higher concentration of inhibitors (furan derivatives, weak acids, and phenolic compounds) in the media, which negatively affect the fermentation performance. One strategy to eliminate soluble inhibitors is filtering and washing the pretreated material. In this study, it was observed that even if the material was previously washed, inhibitory compounds were released during the enzymatic hydrolysis step. Laccase enzymatic treatment was evaluated as a method to reduce these inhibitory effects. The laccase efficiency was analyzed in a presaccharification and simultaneous saccharification and fermentation process at high-substrate loadings. Water-insoluble solids fraction from steam-exploded wheat straw was used as substrate and Saccharomyces cerevisiae as fermenting microorganism. Laccase supplementation reduced strongly the phenolic content in the media, without affecting weak acids and furan derivatives. This strategy resulted in an improved yeast performance during simultaneous saccharification and fermentation process, increasing significantly ethanol productivity.