Abstract
The continuous increase in the world energy and chemicals demand requires the development of sustainable alternatives to non-renewable sources of energy. Biomass facilities and biorefineries represent interesting options to gradually replace the present industry based on fossil fuels. Lignocellulose is the most promising feedstock to be used in biorefineries. From a sugar platform perspective, a wide range of fuels and chemicals can be obtained via microbial fermentation processes, being ethanol the most significant lignocellulose-derived fuel. Before fermentation, lignocellulose must be pretreated to overcome its inherent recalcitrant structure and obtain the fermentable sugars. Usually, harsh conditions are required for pretreatment of lignocellulose, producing biomass degradation and releasing different compounds that are inhibitors of the hydrolytic enzymes and fermenting microorganisms. Moreover, the lignin polymer that remains in pretreated materials also affects biomass conversion by limiting the enzymatic hydrolysis. The use of laccases has been considered as a very powerful tool for delignification and detoxification of pretreated lignocellulosic materials, boosting subsequent saccharification and fermentation processes. This review compiles the latest studies about the application of laccases as useful and environmentally friendly delignification and detoxification technology, highlighting the main challenges and possible ways to make possible the integration of these enzymes in future lignocellulose-based industries.
Highlights
Renewable fuels are considered promising alternatives to mitigate global warming and reduce our dependence on fossil fuels
A detoxification detoxification step step prior prior to to enzymatic enzymatic hydrolysis hydrolysis and/or and/orfermentation fermentationof ofpretreated pretreated materials materials may reduce the concentration of inhibitory compounds, enhancing saccharification and conversion may reduce the concentration of inhibitory compounds, enhancing saccharification and conversion yields
The direct action of laccases on lignin is, in principle, restricted to phenolic units—which only represent a small percentage of the total polymer, different studies have showed the ability of laccase alone for delignifying different pretreated materials, improving the subsequent enzymatic hydrolysis (Table 2)
Summary
Renewable fuels are considered promising alternatives to mitigate global warming and reduce our dependence on fossil fuels. Fermentation 2017, 3, 17 is expected to provide a wide range of different renewable products such as food and feed additives, chemicals and materials This lignocellulose-based industry— known as biorefinery—is likely to become increasingly important in the future society as a complement and/or alternative to the current petroleum-based industry. High pressures and temperatures and/or the addition of chemicals and solvents are in general required These harsh pretreatment conditions lead to biomass degradation and generation of different enzymatic (mainly phenolic compounds) and microbial inhibitors (weak acids, furan derivatives and phenols), which limits the subsequent saccharification and fermentation steps [5]. Another factor that limits enzymatic hydrolysis is the residual lignin that remains in pretreated materials. The present work focuses on review the use of laccases as delignification and detoxification agents for the efficient conversion of lignocellulosic biomass into value-added products, with special accent in the lignocellulosic ethanol production
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