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The physicochemical pretreatment is an important step to reduce biomass recalcitrance and facilitate further processing of plant lignocellulose into bioproducts. This process results in soluble and insoluble biomass fractions, and both may contain by-products that inhibit enzymatic biocatalysts and microbial fermentation. These fermentation inhibitory compounds (ICs) are produced during the degradation of lignin and sugars, resulting in phenolic and furanic compounds, and carboxylic acids. Therefore, detoxification steps may be required to improve lignocellulose conversion by microoganisms. Several physical and chemical methods, such as neutralization, use of activated charcoal and organic solvents, have been developed and recommended for removal of ICs. However, biological processes, especially enzyme-based, have been shown to efficiently remove ICs with the advantage of minimizing environmental issues since they are biogenic catalysts and used in low quantities. This review focuses on describing several enzymatic approaches to promote detoxification of lignocellulosic hydrolysates and improve the performance of microbial fermentation for the generation of bioproducts. Novel strategies using classical carbohydrate active enzymes (CAZymes), such as laccases (AA1) and peroxidases (AA2), as well as more advanced strategies using prooxidant, antioxidant and detoxification enzymes (dubbed as PADs), i.e. superoxide dismutases, are discussed as perspectives in the field.

Biodiesel has become increasingly important in recent years as a potential substitute for petroleum diesel. Different techniques and catalysts have been developed and widely investigated for biodiesel production via enzymatic biocatalysis. In this review, we conducted a bibliometric analysis to examine the global scenario and identify trends in lipase‐catalyzed biodiesel production in the past three decades. Challenges, advantages, disadvantages, and novel methods are also discussed. Publication frequency increased over the studied period, with China, Brazil, and India emerging as the most productive countries in terms of total number of publications and number of publications per journal. Papers from the field of bioenergy and bioprocesses received the highest number of citations. Keyword analysis revealed that immobilized lipase (magnetic nanoparticles and cross‐linked enzyme aggregates), different feedstocks, ionic liquids, ultrasonication, and metabolic engineering were relevant to lipase‐catalyzed biodiesel production. It is concluded that the research emphasis on biodiesel production is moving toward the use of non‐edible oils, ultrasound, and ionic liquids for achieving high‐enzyme activity and substrate conversion. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd

Studies have been conducted on detoxification of hemicellulose hydrolysates, but an effective detoxification method remains to be developed. The use of layered double hydroxides (LDHs) as adsorbents may be a solution to this problem. In this study, LDHs composed of 30, 63, or 70% MgO were used in their uncalcined and calcined states to adsorb acetic acid, formic acid, hydroxymethylfurfural, and furfural from a synthetic hemicellulose hydrolysate. Kinetic studies revealed that calcined LDH composed of 70% MgO (MG70c) had the best performance: it was able to remove 73% of acetic acid and 90% of formic acid in 6 h of incubation at 50 °C. Hydroxymethylfurfural and furfural were not adsorbed (C/C 0 ≈ 1) by calcined or uncalcined LDHs under the studied conditions. The adsorption equilibrium was determined at different temperatures. Adsorption isotherms were best described by the Langmuir−Freundlich model. These results show the potential of MG70c to remove acetic and formic acids from hemicellulose hydrolysates, thereby increasing their suitability as fermentation substrates.

Acetic acid (AA) and formic acid (FA) are two of the major fermentation inhibitors found in hemicellulosic hydrolysates. Their removal, which is necessary for the use of hydrolysates as fermentation substrates, can be achieved by adsorption on hydrotalcites. This study aimed to assess the efficiency of hydrotalcites in removing AA and FA from aqueous solution. Kinetic, thermodynamic, and equilibrium experiments were conducted using hydrotalcites composed of 30, 63, or 70% MgO. Calcined hydrotalcites composed of 70 and 63% MgO (MG70c and MG63c) had the best kinetic performance, removing 97% of FA and 91% of AA. The adsorption process followed pseudo-first-order kinetics. The Boyd model showed that external mass transfer or a combination of intraparticle diffusion and external mass transfer controls the process. Adsorption equilibrium was evaluated at different temperatures (30, 40, 50, and 60 °C) using MG70c as an adsorbent. The Freundlich model provided the best fit to adsorption isotherms. Thermodynamic studies indicated that adsorption was spontaneous and endothermic in nature. The results confirmed the efficiency of MG70c in removing AA and FA from aqueous solution.