Detoxification Of Hydrolysate Research Articles

Detoxification of water hyacinth hydrolysate mediated by exopolysaccharide-based hydrogel enhances hydrogen and methane production

In this study, the exopolysaccharide from cyanobacteria was used for detoxification of acid hydrolysate of water hyacinth biomass. Exopolysaccharide-hydrogel showed phenolics and furans removal of 86 % and 97 %, respectively, with sugar recovery of 98.3 %. The fermentation of detoxified acid hydrolysate was integrated with that of pretreated biomass subjected to enzymatic saccharification derived from commercial cellulose (ESF) or from microbe (MSF). The maximum hydrogen production of 69.2 mL/g-VS was obtained in MSF, which is 1.2- and 1.6-fold higher than ESF and undetoxified acid hydrolysate, respectively. Additionally, the methane production of 12.6 mL/g-VS by mixed methanogenic consortia was obtained using the spent liquor containing volatile fatty acids. This enhanced hydrogen and methane production in subsequent microbial processes is mainly attributed to the selective removal of inhibitors in combination with an integrated carbohydrate utilization.

Optimization of Clostridium beijerinckii semi-solid fermentation of rape straw to produce butyric acid by genome analysis

Butyric acid is a volatile saturated monocarboxylic acid, which is widely used in the chemical, food, pharmaceutical, energy, and animal feed industries. This study focuses on producing butyric acid from pre-treated rape straw using simultaneous enzymatic hydrolysis semi-solid fermentation (SEHSF). Clostridium beijerinckii BRM001 screened from pit mud of Chinese nongxiangxing baijiu was used. The genome of C. beijerinckii BRM001 was sequenced and annotated. Using rape straw as the sole carbon source, fermentation optimization was carried out based on the genomic analysis of BRM001. The optimized butyric acid yield was as high as 13.86 ± 0.77 g/L, which was 2.1 times higher than that of the initial screening. Furthermore, under optimal conditions, non-sterile SEHSF was carried out, and the yield of butyric acid was 13.42 ± 0.83 g/L in a 2.5-L fermentor. This study provides a new approach for butyric acid production which eliminates the need for detoxification of straw hydrolysate and makes full use of the value of fermentation waste residue without secondary pollution, making the whole process greener and more economical, which has a certain industrial potential.Graphical

Biological Detoxification of the Inhibitors in Corncob Acid Hydrolysate Using Aspergillus niger

The biological detoxification of lignocellulose hydrolysate is an effective method through which to enhance microbial fermentation efficiency. In this study, an inhibitor-tolerant strain of A. niger (Aspergillus niger) was used for the biological detoxification of corncob hydrolysate. The results showed that A. niger M13 can tolerate a concentration of at least 7.50 ± 0.19 g/L of acetic acid, 1.81 ± 0.13 g/L of furfural, and 1.02 ± 0.10 g/L of HMF (5-Hydroxymethylfurfural). The spores had a higher detoxification efficiency than the mycelial pellets with a detoxification rate of 0.1566 g/L/h, 0.1125 g/L/h, and 0.015 g/L/h for acetic acid, furfural, and HMF, respectively. The cell preferentially consumed furfural, then HMF, before simultaneously degrading acetic acid and glucose. A. niger M13 spores could accumulate small amounts of citric acid directly from undetoxified hydrolysate at a concentration of about 6 g/L. Therefore, A. niger M13 can serve as an excellent biological detoxification strain and a potential citric acid fermenting strain when using undetoxified lignocellulosic hydrolysates.

Co‐production of biobutanol and biomethane from distillers' grain waste by an integrated process

AbstractBackgroundDistillers' grain waste (DGW) is the main by‐product in the Baijiu‐making process and its management remains a great challenge for the Baijiu industry. To address this issue, an integrated biobutanol and biomethane production process was established to obtain valuable products from DGW and reduce environmental pollution.ResultsIn the integrated process, DGW was hydrolyzed and detoxified to produce biobutanol, while the distillery waste derived from solvent extraction process was used for biomethane fermentation. After the optimization of overliming detoxification of DGW hydrolysate by artificial neural network and genetic algorithm, totals of 10.65 ± 0.07 g L−1 butanol and 4.51 ± 0.21 g L−1 isopropanol were attained with negligible amounts of acetone and ethanol (i.e. 0.14 ± 0.00 and 0.52 ± 0.06 g L−1, respectively). Anaerobic digestion of the distillery waste was efficient, and the chemical oxygen demand removal rate approached 92.3 ± 0.1% with a methane yield of 167.8 ± 1.2 mL g−1 TCODremoved. Moreover, the anaerobic digestion effluent could be recycled as a potential substitute for process water in biobutanol fermentation without having any negative effect on enzymatic hydrolysis of DGW, and the butanol production also reached 8.19 ± 0.29 g L−1.ConclusionThe present study provides a new idea for comprehensive utilization of DGW towards energy and resource recovery, without secondary pollution. © 2023 Society of Chemical Industry.

Two-stage sulfite steam pre-treatment achieves extraordinary bioethanol titer from simultaneously saccharification and fermentation of softwood whole slurries

Softwood biomass, which contains rich portion of readily fermentable sugars, is a type of abundant biomass in Canada and Nordic countries. However, its recalcitrant structure has severely limited its utilization in bioconversion. Sulfite treatment during steam pre-treatment to simultaneously enhance ease of hydrolysis and fermentation of softwood biomass has turned to be an attractive strategy to unlock the possibility of converting softwood to bioethanol. Our previous work showed applying one-stage sulfite treatment during the steam pre-treatment under neutral/alkaline conditions could maximize the sulfonation/delignification and hemicellulose sugar retention, while the use of acidic conditions could enhance the homogenous substrates size reduction. To take the advantages of both the neutral/alkaline and acidic conditions, we developed two-stage sulfite steam pre-treatment to maximize the sugar and ethanol production by utilizing Na2SO3 in the first alkaline steam pre-treatment stage and SO2 in a second acidic steam pre-treatment stage. The resulting substrates showed high sulfonation/delignification extent, nearly 100 % sugar recovery, homogeneous substrates size reduction and sufficient detoxification. Without extra hydrolysate detoxification and concentration, 160 g/L fermentable sugars were obtained from the hydrolysis of two-stage sulfite steam pretreated softwood whole slurry at 25% solid loading. And 80 g/L ethanol was generated by directly fermenting these sugars in the whole slurry hydrolysate without additional detoxification or concentration processes. This work significantly contributed to the development of the industrial relevant bioethanol production from softwood biomass.

Third Generation Lactic Acid Production by Lactobacillus pentosus from the Macroalgae Kappaphycus alvarezii Hydrolysates

The evaluation of macroalgae as a new raw material for diverse bioprocesses is of great interest due to their fast growth rate and low environmental impact. Lactic acid has a high value in the bio-based industry and is mainly produced via fermentation. The anaerobic lactic acid fermentation of Kappaphycus alvarezii hydrolysates using the high-producing strain Lactobacillus pentosus was evaluated for detoxified and non-treated hydrolysates prepared from concentrated algal biomass and dilute acid solution mixtures. A novel hydrolysate detoxification procedure, combining activated charcoal and over-liming, for 5-hydroxymethylfurfural (HMF) removal was used. L. pentosus was found to successfully ferment detoxified and untreated hydrolysates produced in up to 30% and 20% w/v solutions, respectively. Significant production rates (1.88 g/L.h) and short lag phases were achieved in bioreactor fermentation operating at 37 °C and pH 6 with 150 rpm impeller velocity. A 0.94 g/g yield from fermentable sugars (galactose and glucose) was achieved, indicating that K. alvarezii could be used as a raw material for lactic acid production, within the context of Third Generation (3G) biorefinery.

Evaluation of Preparation and Detoxification of Hemicellulose Hydrolysate for Improved Xylitol Production from Quinoa Straw

Quinoa straw is rich in hemicellulose, and it could be hydrolyzed into xylose. It is a promising energy resource alternative that acts as a potential low-cost material for producing xylitol. In this study, quinoa straw was used as a substrate subjected to the hydrolysis of dilute sulfuric acid solution. Based on the production of xylose and inhibitors during hydrolysis, the optimal conditions for the hydrolysis of hemicellulose in quinoa straw were determined. Detoxification was performed via activated carbon adsorption. The optimal detoxification conditions were determined on the basis of major inhibitor concentrations in the hydrolysate. When the addition of activated carbon was 3% at 30 °C for 40 min, the removal of formic acid, acetic acid, furfural, and 5-HMF could reach 66.52%, 64.54%, 88.31%, and 89.44%, respectively. In addition to activated carbon adsorption, vacuum evaporation was further conducted to perform two-step detoxification. Subsequently, the detoxified hydrolysate was used for xylitol fermentation. The yield of xylitol reached 0.50 g/g after 96 h of fermentation by Candida tropicalis (CICC 1779). It is 1.2-fold higher than that obtained through the sole vacuum evaporation method. This study validated the feasibility of xylitol production from quinoa straw via a biorefinery process.

Detoxification of hemicellulose-enriched hydrolysate from sugarcane bagasse by activated carbon and macroporous adsorption resin

Detoxification of hemicellulose-enriched hydrolysate from sugarcane bagasse by activated carbon and macroporous adsorption resin

Enzymatic formulation strategies unlock highly-efficient saccharification of distinct pretreated corncobs

Optimization of the composition of enzyme cocktail is an effective way to improve the hydrolytic efficiency and reduce the cost during enzymatic hydrolysis of lignocellulose. Herein, the optimal enzymes ratios of enzyme cocktails for efficient hydrolysis of corncobs with distinct pretreatments were quantitatively formulated. As the importance of pretreatment type on xylan extraction, the optimized cellulase/hemicellulase ratios for NaClO2, H2SO4 and steam explosion treated corncob were 1:1.5, 1:0.15 and 1:0.75, respectively. Meanwhile, different requirements for types of cellulases are also determined: endoglucanase and cellobiohydrolase were key enzymes in the hydrolysis of NaClO2 and H2SO4 treated corncobs, respectively, while the synergy of three kinds of cellulases was preferred for steam-exploded corncob. Furthermore, based on the optimized cellulase/hemicellulase ratios, cellulases proportions for hydrolyzing the corncobs pretreated with distinctive methods were determined. Notably, by the enzymatic formulation strategy, 100% yields of glucose and xylose were obtained simultaneously from NaClO2 treated corncob, which was up to 70.1% and 80.1% at high solid loading (20%), respectively. Without detoxification of hydrolysate, high isopropanol yield of 0.45 g/g (of dry matter) was achieved. Hence, this study demonstrated a low cost and high efficient conversion strategy for prospective high-value utilization of lignocellulose.

Cardoon Hydrolysate Detoxification by Activated Carbon or Membranes System for Bioethanol Production

Advanced biofuels incorporation into the transportation sector, particularly cellulosic bioethanol, is crucial for attaining carbon neutrality by 2050, contributing to climate changes mitigation and wastes minimization. The world needs biofuel to be commercially available to tackle the socioeconomic challenges coming from the continued use of fossil fuels. Cynara cardunculus (cardoon) is a cheap lignocellulosic raw biomass that easily grows in Mediterraneous soils and is a potential renewable resource for a biorefinery. This work aimed to study the bioethanol production from cardoon hemicellulosic hydrolysates, which originated from dilute sulfuric acid hydrolysis pretreatment. A detoxification step to remove released microbial fermentative inhibitors was evaluated by using both activated carbon adsorption and a nanofiltration membrane system. The Scheffersomyces stipitis CBS5773 yeast and the modified Escherichia coli MS04 fermentation performances at different experimental conditions were compared. The promising results with E. coli, using detoxified cardoon by membrane nanofiltration, led to a bioethanol volumetric productivity of 0.30 g·L−1·h−1, with a conversion efficiency of 94.5%. Regarding the S. stipitis, in similar fermentation conditions, volumetric productivity of 0.091 g·L−1·h−1 with a conversion efficiency of 64.9% was obtained. Concluding, the production of bioethanol through detoxification of hemicellulosic cardoon hydrolysate presents a suitable alternative for the production of second-generation bioethanol, especially using the modified E. coli.

Production of single cell oil by Yarrowia lipolytica JCM 2320 using detoxified desiccated coconut residue hydrolysate.

Nowadays, the replacement of petro-diesel with biodiesel has raised the concern among the community for the utilization of improper feedstocks and the cost involved. However, these issues can be solved by producing single cell oil (SCO) from lignocellulosic biomass hydrolysates by oleaginous microorganisms. This study introduced Yarrowia lipolytica JCM 2320 with a desiccated coconut residue (DCR) hydrolysate (obtained from the 2% dilute sulphuric acid pretreatment) as a carbon source in generating SCO. However, common inhibitors formed during acid pretreatment of biomass such as five-hydroxymethylfurfural (HMF), furfural, acetic acid and levulinic acid resulting from the sugar degradations may have detrimental effects towards the fermentation process. To visualize the effect of inhibitors on Y. lipolytica, an inhibitory study was conducted by adding 0.5–5.0 g/L of potential inhibitors to the YPD (yeast, peptone and D-glucose) medium. It was found that the presence of furfural at 0.5 g/L would increase the lag phase, which beyond that was detrimental to Y. lipolytica. Furthermore, increasing the five-hydroxymethylfurfural (HMF) concentration would increase the lag phase of Y. lipolytica, whereas, for acetic acid and levulinic acid, it showed a negligible effect. Detoxification was hence conducted to remove the potential inhibitors from the DCR hydrolysate prior its utilization in the fermentation. To examine the possibility of using adsorption resins for the detoxification of DCR hydrolysate, five different resins were tested (Amberlite® XAD-4, Amberlite® XAD-7, Amberlite® IR 120, Amberlite® IRA 96 and Amberlite® IRA 402) with five different concentrations of 1%, 3%, 5%, 10% and 15% (w/v), respectively. At resin concentration of 10%, Amberlite® XAD-4 recorded the highest SCO yield, 2.90 ± 0.02 g/L, whereas the control and the conventional overliming detoxification method, recorded only 1.29 ± 0.01 g/L and 1.27 ± 0.02 g/L SCO accumulation, respectively. Moreover, the fatty acid profile of the oil produced was rich in oleic acid (33.60%), linoleic acid (9.90%), and palmitic acid (14.90%), which indicates the potential as a good biodiesel raw material.

Process development for detoxification of corncob hydrolysate using activated charcoal for xylitol production

The work describes process development for detoxification of corncob hydrolysate using activated carbon for microbial xylitol production. Activated carbon was used as an adsorbent to completely remove the major fermentation inhibitors obtained during dilute acid and steam explosion of biomass. A xylitol yield of 0.78 g/g was achieved from the detoxified hydrolysate in a 5 L fermenter by Pichia caribbica. The spent carbon was effectively regenerated and used for three consecutive cycles of operation. The successive regeneration and reuse of carbon could reduce the operational cost by ~ 38% and be used as a reference dataset for process scale-up and cost-effective xylitol production.

Bioprocessing of fermentable sugars derived from water hyacinth into microbial lipids and single cell proteins by oleaginous yeast Rhodosporidium toruloides NCIM 3547

In this study, we employed microwave-acid pretreatment for water hyacinth (WH) to obtain liquid hydrolysate that contains sugars derived from holocellulosic components of biomass for further oleaginous yeast fermentation. In order to remove the inhibitors such as furans after acid treatment, detoxification of hydrolysate was done and we compared the efficiency of this step with non-detoxified hydrolysate towards capability of the Rhodosporidium toruloides NCIM 3547 (an oleaginous yeast) to produce microbial lipid and single cell protein. The results indicated that the reducing sugar concentration was found to be higher in non-detoxified hydrolysate (65.41 g/L) than detoxified one (59.18 g/L). When the non-detoxified liquid hydrolysate was supplemented with yeast extract as a complex organic source for R. toruloides, resulted in a maximum lipid yield of about 0.813 ± 0.041 (g/g) and 53.60 ± 2.68 (g/g) of single cell protein content with 0.038 g/L/d of protein productivity. Two kinetic models, hybrid Logistic-Monod and Luedeking-Piret, were employed to assess the microbial growth and the substrate utilization that were found to be in well agreement with the experimental data with a coefficient of determination (R2) value ranging from 0.95 to 0.99 thereby demonstrating the efficiency of the hydrolysate supplemented media. Furthermore, GC-MS analysis of transesterified lipids revealed the presence of various FAME (fatty acid methyl esters) and also the presence of increased levels of total saturated fatty acids (35.03%) advocates its high potential in biodiesel production. This study demonstrates the feasibility of sustainable valorization of WH-derived liquid hydrolysate towards a greener biorefinery framework.Graphical abstract

Co-cultivation of a novel Fusarium striatum strain and a xylose consuming Saccharomyces cerevisiae yields an efficient process for simultaneous detoxification and fermentation of lignocellulosic hydrolysates

Furfural (FF) and 5-hydroxymethylfurfural (HMF) are furan derivatives commonly generated during the pretreatment of lignocellulosic biomass and often considered among the most inhibitory compounds towards the sugar fermenting strains due to their acute toxicity and high concentrations. The present study describes the simultaneous detoxification and fermentation of lignocellulosic hydrolysates containing high concentrations of FF and HMF by a co-culture of a novel Fusarium striatum strain and a xylose consuming Saccharomyces cerevisiae strain. The process demonstrates a superior performance than those previously described in the literature, as FF and HMF were efficiently transformed into their less toxic added-value alcohol derivatives by F. striatum with high yields (99% and 86%, respectively) and the higher detoxification rates reported (0.56 g/L/h and 0.13 g/L/h, respectively). There was no sugar consumption by the filamentous fungus during the detoxification process, rendering it available for ethanol fermentation by S. cerevisiae, which started immediately after the detoxification of the inhibitors. Ethanol productivities were significantly higher when increasing the inoculum size of F. striatum, confirming its potential for the detoxification of the lignocellulosic hydrolysate. High ethanol yields (0.4 g/g) and productivities (0.46 g/L/h) were obtained in a bench-scale bioreactor (1.5 L) in the presence of 3.5 g/L HMF and 2.5 g/L FF, a concentration of furan derivatives that completely inhibited the fermentation process in the absence of F. striatum. The presented process allows access to lignocellulosic materials and pretreatment methods that result in high concentrations of FF and HMF that are currently not feasible, representing a significant advance for the lignocellulosic ethanol industry.

Use of dry yeast biomass as a new approach for detoxification of hemicellulosic hydrolysates aiming to xylitol production

The presence of toxic compounds in hemicellulosic hydrolysates is a bottleneck for biotechnological processes, such as xylitol production. In our work, a new approach was proposed for hemicellulosic hydrolysates detoxification by using the residual dry yeast biomass (DYB) from xylitol production bioprocess. Candida tropicalis biomass was recovered from fermentation process of a medium based on sugarcane bagasse and straw hemicellulosic hydrolysate (SBSH). The effects of influent variables on detoxification performance were investigated, and the removal of phenolic compounds, acetic acid, furfural and 5-hydroxymethylfurfural reached up to, respectively, 27.0 %, 26.7 %, 27.5 %, and 25.8 %. By using the SBSH detoxified at conditions of highest phenolics removal, fermentations (initial xylose concentration of 52 g L−1) were performed for xylitol production, resulting in a yield of 0.79 gg-1 and 86 % of conversion efficiency. Thus, the use of residual DYB is a potential alternative for detoxification of hemicellulosic hydrolysates, since recycling the biomass could reduce the expenditures with adsorbents.

Atmospheric cold plasma-assisted pineapple peel waste hydrolysate detoxification for the production of bacterial cellulose

Toxic compounds in pineapple peel waste hydrolysate (PPWH), namely formic acid, 5-hydroxymethylfurfural (HMF), and furfural, are the major predicament in its utilization as a carbon source for bacterial cellulose (BC) fermentation. A rapid detoxification procedures using atmospheric cold plasma (ACP) technique were employed to reduce the toxic compounds. ACP treatment allows the breakdown of toxic compounds without causing excessive breakdown of sugars. Herein, the performance of two available laboratory ACP reactors for PPWH detoxification was being demonstrated. ACP-reactor-1 (R1) runs on plasma power of 80–200 W with argon (Ar) plasma source, while ACP-reactor-2 (R2) runs at 500–600 W with air plasma source. Treatment in R1, at 200 W for 15 min, results in 74.06%, 51.38%, and 21.81% reduction of furfural, HMF, and formic acid. Treatment in R2 at 600 W gives 45.05%, 32.59%, and 60.41% reductions of furfural, HMF, and formic acid. The BC yield from the fermentation of Komagateibacter xylinus in the R1-treated PPWH, R2-treated PPWH, and untreated-PPWH is 2.82, 3.82, and 2.97 g/L, respectively. The results show that ACP treatment provides a novel detoxified strategy in achieving agricultural waste hydrolysate reuse in fermentation. Furthermore, the results also imply that untreated PPWH can be an inexpensive and sustainable resource for fermentation media supplementation.

Effect of the Sugarcane Bagasse Deacetylation in the Pentoses Fermentation Process

Biomass alkaline deacetylation prior to acid pretreatment can be a promising alternative to reduce the toxicity of hemicellulosic hydrolysates and improve second-generation bioethanol production. In this paper, the effect of alkaline deacetylation of sugarcane bagasse on bioethanol production by Spathaspora passalidarum was evaluated. Sugarcane bagasse deacetylated hemicellulosic hydrolysate (DHH) was processed using the following sequence: (1) deacetylation (0.4%, w/v NaOH, 70 °C, 3 h) and (2) acid pretreatment (0.5% (v/v) of H2SO4, 140 °C, 15 min). Non-deacetylated, hemicellulosic hydrolysate (HH), was obtained applying only acid pretreatment (0.5% (v/v) of H2SO4, 140 °C, 15 min). Biomass deacetylation reduced the content of acetic acid and some phenolic compounds in the hydrolysate (DHH) compared to acid pretreatment (HH), which resulted in its low toxicity. Thus, the bioethanol production with DHH was of 16.92 g L−1, whereas only 1.3 g L−1 of bioethanol was obtained with HH fermentation. Deacetylation process provided a 13-fold increase in bioethanol production by S. passalidarum, showing that alkaline deacetylation followed by sulfuric acid pretreatment is a promising strategy to increase bioethanol production. This procedure provided a simple and practical alternative to the classic methods of detoxification of hemicellulosic hydrolysate from sugarcane bagasse.

Photo-fermentative hydrogen production by Rhodopseudomonas palustris CGA009 in the presence of inhibitory compounds

This study investigated Rhodopseudomonas palustris CGA009 biohydrogen production from compounds commonly found in lignocellulosic steam explosion hydrolysate, by examining the effect of individual inhibitory phenolic and furan compounds found in hydrolysates, under photo-fermentative anaerobic conditions. Since lignocellulose is often converted into ethanol via yeast-mediated fermentation, the tolerance of R. palustris CGA009 towards ethanol inhibition was also tested at a concentration range of 0.25–14% (v/v) under anaerobic photo-fermentative conditions. Hydrogen production was enhanced by compounds such as syringaldehyde (0.03 g/L), which accumulated total hydrogen of 960 mL over the cultivation period. In contrast, a reduction in hydrogen production of 1.4 fold was observed in vanillin-containing solutions (0.43 g/L), which obtained accumulated total hydrogen of 576 mL. Increasing ethanol concentrations reduced hydrogen production, but cell growth was not affected up to 1% (v/v), a fairly low concentration. R. palustris CGA009 can tolerate comparatively high concentrations of phenolic compounds, suggesting its use for lignocellulose hydrolysate detoxification and hydrogen production.

Acid hydrolysis optimization of pomegranate peels waste using response surface methodology for ethanol production

Agro-industrial wastes can be processed into valuable products. Successively, current investigation is an effort to optimize the acid hydrolysis of pomegranate peels waste (PPW) using central composite design (CCD) of response surface methodology (RSM) for ethanol production. Concentration of sulfuric acid, temperature, and time of hydrolysis were used as dependent variables, whereas reducing sugars, total carbohydrates, extractives, weight loss, hemicellulose, cellulose, and lignin contents were recorded as responses for PPW decomposition. The highest glucose level of 0.56 ± 0.04 mg mL−1 (with 5% acid concentration at 100 °C for 30 min) and carbohydrate contents of 1.53 ± 0.07 mg mL−1 (with 3% acid concentration at 75 °C for 45 min) were obtained. Subsequently, detoxification of hydrolysate was conducted employing 2.5% activated charcoal that reduced 62% of phenolic compounds. Detoxified hydrolysate was subjected to fermentation by ethanologenic yeasts: Metschnikowia sp. Y31, Metschnikowia cibodasensis Y34, and Saccharomyces cerevisiae K7 for 10 days experiment. Significant ethanol yield of 0.42 ± 0.08 g g−1 was noticed by Metschnikowia sp. Y31 on day 5 and 0.41 ± 0.07 g g−1 for Metschnikowia cibodasensis Y34 on day 2. The results demonstrated the hopeful prospect for bioethanologenesis using cellulosic wastes at marketable level.

Enzymatic removal of inhibitory compounds from lignocellulosic hydrolysates for biomass to bioproducts applications.

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.