Production and extraction optimization of xylanase and β-mannanase by Penicillium chrysogenum QML-2 and primary application in saccharification of corn cob

Fusion of Oligopeptide to the C Terminus of α-Glucuronidase from Thermotoga maritima Improves the Catalytic Efficiency for Hemicellulose Biotransformation

Fusion protein combined the oligopeptide (HQAFFHA) with the C terminus of α-glucuronidase from Thermotoga maritima was produced in E. coli and purified for characterization and applications of glucuronic and glucaric acid production. The fusion protein with oligopeptide exhibited a 2.97-fold higher specific activity than individual protein. Their catalytic efficiency k_cat/K_m and k_cat increased from 469.3 ± 2.6 s^-1 (g mL^-1)^-1 and 62.4 ± 0.9 s^-1 to 2209.5 ± 26.3 s^-1 (g mL^-1)^-1 and 293.9 ± 4.9 s^-1, respectively. Fusion protein had similar temperature and pH profiles to those without oligopeptide, but the thermal stability decreases and the pH stability shifts to alkaline. Using beech xylan hydrolysate as a substrate, the glucuronic acid yield of fusion enzyme increased by 9.94% compared with its parent at 65 °C pH 8.5 for 10 h, and can hydrolyze corn cob xylan with xylanase to obtain glucuronic acid, and can be combined with uronate dehydrogenase to obtain high-added value glucaric acid. Homologous modeling analysis revealed the factors contributing to the high catalytic efficiency of fusion enzyme. These results show that the peptide fusion strategy described here may be useful for improving the catalytic efficiency and stability of other industrial enzymes, and has great potential for producing high value-added products from agricultural waste.

Fusarium graminearum as a producer of xylanases with low cellulases when grown on wheat bran

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Endophytic fungi of cacao had important xylanase activity when grown on wheat bran.

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F. graminearum strain Ec220 produced xylanases with low cellulolytic activity.

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Xylanase production was optimized using response surface methodology.

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Proteomic analysis revealed similarities with previously reported xylanases.

The xylanolytic potential of endophytic fungi isolated from leaves of Theobroma cacao was explored for the first time. Four fungal strains showed significant amounts of xylanase activity and low cellulase levels when grown on wheat bran as the sole carbon source. Strain Ec220 of Fusarium graminearum had the highest xylanase production (1.79 U/ml), whereas its cellulase activity was minimal (0.24 U/ml). Optimal conditions for xylanase production were: 154 h of incubation time, pH 5.79 and 29.8 °C. Furthermore, two protein spots detected by two-dimensional gel electrophoresis showed molecular weights (26.05 and 27.70 kDa) and isoelectric points (6.18 and 9.20) corresponding to previously reported F. graminearum xylanases, Xyl A and Xyl B, respectively. Therefore, endophytic fungi of T. cacao can be an important source of xylanolytic activities when cultured on wheat bran, and xylanases with low cellulases found in strain Ec220 require further characterization as they show promise for possible industrial applications.

Fungal Lignocellulose Utilisation Strategies from a Bioenergetic Perspective: Quantification of Related Functional Traits Using Biocalorimetry

In the present study, we investigated whether a non-invasive metabolic heat flux analysis could serve the determination of the functional traits in free-living saprotrophic decomposer fungi and aid the prediction of fungal influences on ecosystem processes. For this, seven fungi, including ascomycete, basidiomycete, and zygomycete species, were investigated in a standardised laboratory environment, employing wheat straw as a globally relevant lignocellulosic substrate. Our study demonstrates that biocalorimetry can be employed successfully to determine growth-related fungal activity parameters, such as apparent maximum growth rates (AMGR), cultivation times until the observable onset of fungal growth at AMGR (t_AMGR), quotients formed from the AMGR and t_AMGR (herein referred to as competitive growth potential, CGP), and heat yield coefficients (Y_Q/X), the latter indicating the degree of resource investment into fungal biomass versus other functional attributes. These parameters seem suitable to link fungal potentials for biomass production to corresponding ecological strategies employed during resource utilisation, and therefore may be considered as fungal life history traits. A close connection exists between the CGP and Y_Q/X values, which suggests an interpretation that relates to fungal life history strategies.

Application of free and immobilized novel bifunctional biocatalyst in biotransformation of recalcitrant lignocellulosic biomass

Herein, an innovative, green, and practical biocatalyst was developed using conjugation of a novel bifunctional mannanase/xylanase biocatalyst (PersiManXyn1) to the modified cellulose nanocrystals (CNCs). Firstly, PersiManXyn1 was multi-stage in-silico screened from rumen macrobiota, and then cloned, expressed, and purified. Next, CNCs were synthesized from sugar beet pulp using enzymatic and acid hydrolysis processes, and then Fe₃O₄ NPs were anchored on their surface to produce magnetic CNCs (MCNCs). This hybrid was modified by dopamine providing DA/MCNCs nano-carrier. The bifunctional PersiManXyn1 demonstrated the superior hydrolysis activity on corn cob compared with the monofunctional xylanase enzyme (PersiXyn2). Moreover, the immobilization of PersiManXyn1 on the nano-carrier resulted in an improvement of the thermal stability, kinetic parameters (K_cat), and storage stability of the enzyme. Incorporation of the Fe₃O₄ NPs on the CNCs made magnetic nano-carrier with high magnetization value (25.8 emu/g) which exhibited rapid response toward the external magnetic fields. Hence, the immobilized biocatalyst could be easily separated from the products by a magnet, and reused up to 8 cycles with maintaining more than 50% of its original activity. The immobilized PersiManXyn1 generated 22.2%, 38.7%, and 35.1% more reducing sugars after 168 h hydrolysis of the sugar beet pulp, coffee waste, and rice straw, respectively, compared to the free enzyme. Based on the results, immobilization of the bifunctional PersiManXyn1 exhibited the superb performance of the enzyme to improve the conversion of the lignocellulosic wastes into high value products and develop the cost-competition biomass operations.

Enhanced β-mannanase production by Bacillus licheniformis by optimizing carbon source and feeding regimes

Bacillus licheniformis HDYM-04 was isolated in flax retting water and showed β-mannanase activity. Carbon sources for β-mannanase production, as well as the fermentation conditions and feeding strategy, were optimized in shake flasks. When glucose or konjac powder was used as the carbon source, the β-mannanase activity was 288.13 ± 21.59 U/mL and 696.35 ± 23.47 U/mL at 24 h, respectively, which was approximately 4.4- to 10.68-fold higher than the values obtained with wheat powder. When 0.5% (w/v) glucose and 1% (w/v) konjac powder were added together, maximum enzyme activities of 789.07 ± 25.82 U/mL were obtained, an increase of 13.35% compared to the unoptimized cultures with only 1% (w/v) konjac powder. The enzyme activity decreased in the presence of 1% (w/v) konjac powder, but the highest enzyme activity was 1,533.26 ± 33.74 U/mL, a 1.2-fold increase compared with that in nonoptimized cultures; when 0.5% (w/v) glucose was used, the highest enzyme activity was 966.53 ± 27.84 U/mL, an increase in β-mannanase activity of 38.79% compared with control cultures. In this study, by optimizing fed-batch fermentation conditions, the yield of β-mannanase produced by HDYM-04 was increased, laying the foundation for the industrial application and further research of B. licheniformis HDYM-04.

Functional and structural investigation of a novel β-mannanase BaMan113A from Bacillus sp. N16-5

Mannan is an important renewable resource whose backbone can be hydrolyzed by β-mannanases to generate manno-oligosaccharides of various sizes. Only a few glycoside hydrolase (GH) 113 family β-mannanases have been functionally and structurally characterize. Here, we report the function and structure of a novel GH113 β-mannanase from Bacillus sp. N16-5 (BaMan113A). BaMan113A exhibits a substrate preference toward manno-oligosaccharides and releases mannose and mannobiose as main hydrolytic products. The crystal structure of BaMan113A suggest that the enzyme shows a semi-enclosed substrate-binding cleft and the amino acids surrounding the +2 subsite form a steric barrier to terminate the substrate-binding tunnel. Based on these structural features, we conducted mutagenesis to engineer BaMan113A to remove the steric hindrance of the substrate-binding tunnel. We found that F101E and N236Y variants exhibit increased specific activity toward mannans comparing to the wild-type enzyme. Meanwhile, the product profiles of these two variants toward polysaccharides changed from mannose to a series of manno-oligosaccharides. The crystal structure of variant N236Y was also determined to illustrate the molecular basis underlying the mutation. In conclusion, we report the functional and structural features of a novel GH113 β-mannanase, and successfully improved its endo-acting activity by using structure-based engineering.

Biochemical characterization and enhanced production of endoxylanase from thermophilic mould Myceliophthora thermophila

Endoxylanase production from M. thermophila BJTLRMDU3 using rice straw was enhanced to 2.53-fold after optimization in solid state fermentation (SSF). Endoxylanase was purified to homogeneity employing ammonium sulfate precipitation followed by gel filtration chromatography and had a molecular mass of ~ 25 kDa estimated by SDS-PAGE. Optimal endoxylanase activity was recorded at pH 5.0 and 60 °C. Purified enzyme showed complete tolerance to n-hexane, but activity was slightly inhibited by other organic solvents. Among surfactants, Tweens (20, 60, and 80) and Triton X 100 slightly enhanced the enzyme activity. The V_max and K_m values for purified endoxylanase were 6.29 µmol/min/mg protein and 5.4 mg/ml, respectively. Endoxylanase released 79.08 and 42.95% higher reducing sugars and soluble proteins, respectively, which control after 48 h at 60 °C from poultry feed. Synergistic effect of endoxylanase (100 U/g) and phytase (15 U/g) on poultry feed released higher amount of reducing sugars (58.58 mg/feed), soluble proteins (42.48 mg/g feed), and inorganic phosphate (28.34 mg/feed) in contrast to control having 23.55, 16.98, and 10.46 mg/feed of reducing sugars, soluble proteins, and inorganic phosphate, respectively, at 60 °C supplemented with endoxylanase only.

Microbial detoxification of mycotoxins in food and feed

Mycotoxins are metabolites produced by fungi growing in food or feed, which can produce toxic effects and seriously threaten the health of humans and animals. Mycotoxins are commonly found in food and feed, and are of significant concern due to their hepatotoxicity, nephrotoxicity, carcinogenicity, mutagenicity, and ability to damage the immune and reproductive systems. Traditional physical and chemical detoxification methods to treat mycotoxins in food and feed products have limitations, such as loss of nutrients, reagent residues, and secondary pollution to the environment. Thus, there is an urgent need for new detoxification methods to effectively control mycotoxins and treat mycotoxin pollution. In recent years, microbial detoxification technology has been widely used for the degradation of mycotoxins in food and feed because this approach offers the potential for treatment with high efficiency, low toxicity, and strong specificity, without damage to nutrients. This article reviews the application of microbial detoxification technology for removal of common mycotoxins such as Aflatoxin, Ochratoxin, Zearalenone, Deoxynivalenol, and Fumonisins, and discusses the development trend of this important technology.

Applications of Microbial β-Mannanases

Mannans are main components of hemicellulosic fraction of softwoods and they are present widely in plant tissues. β-mannanases are the major mannan-degrading enzymes and are produced by different plants, animals, actinomycetes, fungi, and bacteria. These enzymes can function under conditions of wide range of pH and temperature. Applications of β-mannanases have therefore, been found in different industries such as animal feed, food, biorefinery, textile, detergent, and paper and pulp. This review summarizes the most recent studies reported on potential applications of β-mannanases and bioengineering of β-mannanases to modify and optimize their key catalytic properties to cater to growing demands of commercial sectors.

Alkali-stable GH11 endo-β-1,4 xylanase (XynB) from Bacillus subtilis strain CAM 21: application in hydrolysis of agro-industrial wastes, fruit/vegetable peels and weeds

GH11 endo-xylanases, due to their inherent structural and biochemical properties, are the key to efficient bioconversion of lignocellulosic biomass into value-added products. A GH11 endo-xylanase (XynB) from Bacillus subtilis strain CAM 21 was cloned, over-expressed and purified (Mw∼24 kDa) using Ni-NTA affinity chromatography. XynB showed optimum activity at pH 7.0 and 50°C and was stable (>88%) in a broad range of pH (4-11). The apparent Km_, K_cat and K_cat/Km of XynB were 2.9 mg/ml, 1961.2/sec, and 675.62 ml/mg/sec, respectively using birchwood xylan as substrate. XynB was a classical endo-xylanase as it hydrolyzed birchwood xylan to xylo-oligosaccharides and not xylose. Kinetic stability of XynB at 45-53°C was between 43-182 min. Secondary structure analysis of XynB using far-UV CD spectroscopy revealed presence of 51.85% β strands and 2.64% α helix and was consistent with the homology modeling studies. XynB hydrolyzed the xylan extracted from agro-industrial wastes and fruit/vegetable peels by releasing up to 670 mg/g of reducing sugars. The xylan extracted from weeds (Ageratum conyzoides, Achyranthes aspera and Tridax procumbens) had characteristic signatures of hemicelluloses and after XynB hydrolysis showed cracks, peeling and release of up to 135.2 mg/g reducing sugars.

Detoxification of Ochratoxin A by a novel Aspergillus oryzae strain and optimization of its biodegradation

The mycotoxin Ochratoxin A (OTA) causes serious health risks and is found in food products throughout the world. The most promising method to detoxify this compound is biodegradation. In this study, Aspergillus oryzae strain M30011 was isolated and characterized based on its considerable capacity to degrade OTA. The degradation product (compound I) of A. oryzae-treated OTA was isolated, and its toxicity response was also evaluated. Furthermore, the relationships between three key cultivation condition factors affecting the OTA degradation rate were examined using the response surface methodology (RSM). Compound I was identified as ochratoxin α (C₁₁H₉O₅Cl), and the toxicity response experiments indicated that A. oryzae detoxified OTA to a great extent. A maximum degradation rate of 94% was observed after 72h. This study demonstrates the potential for using A. oryzae to detoxify OTA and suggests that it could be applied in the food industry to improve food safety and quality.

Yellow mombin and jackfruit seeds residues applied in the production of reducing sugars by a crude multi-enzymatic extract produced by Penicillium roqueforti ATCC 101110

BACKGROUND

As an alternative to the use of widely investigated agro-industrial residues, the present study aimed to promote the valorization of two selected residues, yellow mombin seed (YS) and jackfruit seed (JS), as a result of their enhanced performance.

RESULTS

YS was applied as a solid state substrate for Penicillium roqueforti ATCC 101110 cultivation (25 °C, A_w = 0.963, 10⁷ spores g^-1 and 142 h) to produce a crude multi-enzymatic extract (CE-YS) containing activities of CMCase = 31.95 U g^-1 , xylanase = 56.85 U g^-1 , exoglucanase = 5.55 U g^-1 and FPase = 24.60 U g^-1 . CE-YS was then applied to six different residues saccharification and the best performance was obtained with jackfruit seed residue (JS), which was selected for enzymatic saccharification. The highest productivity of reducing sugars expressed as glucose (6.26 mg g^-1 h^-1 ) was obtained under the conditions: 40.7 g L^-1 JS, 5 mmol L^-1 MgCl₂ , 65 °C, 120 rpm, pH 3.0 (citrate buffer 50 mmol L^-1 ) and 18 h.

CONCLUSION

The residues, YS and JS, can be used satisfactorily for the production of bioproducts of great industrial applicability, such as crude extracts (containing cellulolytic enzymes) and RS (which can be converted, for example, into bioethanol). © 2020 Society of Chemical Industry.

A novel and cost-effective methodology for enhanced production of industrially valuable alkaline xylano-pectinolytic enzymes cocktail in short solid-state fermentation cycle

The aim of this study was to enhance the production of xylano-pectinolytic enzymes concurrently and also to reduce the fermentation period. In this study, the effect of agro-residues extract-based inoculum on yield and fermentation time of xylano-pectinolytic enzymes was studied. Microbial inoculum and fermentation media were supplemented with xylan and pectin polysaccharides derived from agro-based residues. Enzymes production parameters were optimized through two-stage statistical design approach. Under optimized conditions (temperature 37°C, pH 7.2, K₂ HPO₄ 0.22%, MgSO₄ 0.1%, gram flour 5.6%, substrate: moisture ratio 1:2, inoculum size 20%, agro-based crude xylan in production media 0.45%, and agro-based crude xylan-pectin in inoculum 0.13%), nearly 28,255 ± 565 and 9,202 ± 193 IU of xylanase and pectinase, respectively, were obtained per gram of substrate in a time interval of 6 days only. The yield of both xylano-pectinolytic enzymes was enhanced along with a reduction of nearly 24 h in fermentation time in comparison with control, using polysaccharides extracted from agro-residues. The activity of different types of pectinase enzymes such as exo-polymethylgalacturonase (exo-PMG), endo-PMG, exo-polygalacturonase (exo-PG), endo-PG, pectin lyase, pectate lyase, and pectin esterase was obtained as 1,601, 12.13, 5637, 24.86, 118.62, 124.32, and 12.56 IU/g, respectively, and was nearly twofold higher than obtained for all seven types in control samples. This is the first report mentioning the methodology for enhanced production of xylano-pectinolytic enzymes in short solid-state fermentation cycle using agro-residues extract-based inoculum and production media.

Enhanced endoxylanase production by Myceliophthora thermophila with applicability in saccharification of agricultural substrates

The production of enzymes by solid-state fermentation is an interesting process and currently used worldwide as it can be carried out in solid matrix in absence of free water. In present study, Myceliophthora thermophila BJTLRMDU3 produced high titres of endoxylanase (890.55 U/g DR, dry residue) using 5 g rice straw at pH 7.0 and at 45 °C with 1:7 (w/v) solid-to-moisture ratio with inoculum rate of 12 × 10⁶ spores/ml after 4 days in solid-state fermentation. High enzyme titre was produced after moistening the rice straw with solution containing ammonium sulphate (0.4%), K₂HPO₄ (1.0%), MgSO₄·7H₂O (0.3%), FeSO₄·7H₂O (0.03%) and CaCl₂ (0.03%). Addition of sucrose (2% w/v) and ammonium nitrate (2% w/v) further enhanced the endoxylanase production. A high endoxylanase production was achieved at water activity (a _W) of 0.95 (1639.80 U/g DR) that declined drastically below this value. Among different surfactants, Tween 20 (3% v/v) enhanced the secretion of endoxylanase (2047.91 U/g DR). Furthermore, on optimization of K₂HPO₄ concentration, it was found that 0.5% K₂HPO₄ improved (2191.28 U/g DR) endoxylanase production and overall 4.35-folds increase in production of endoxylanase was achieved after optimization of culture conditions. The enzyme has potential to liberate monomeric (xylose) as well as oligomeric (xylotiose, xylotetrose, and xylopantose) sugars from xylan. On saccharification of rice straw and corncob with endoxylanase, maximum yield of reducing sugars was 135.61 and 132.61 mg/g of substrate recorded after 48, and 36 h, respectively.

Simultaneous production of industrially important alkaline xylanase-pectinase enzymes by a bacterium at low cost under solid-state fermentation conditions

Simultaneous production of alkaline xylanase and all seven types of pectinases by a bacterial isolate, under solid-state fermentation was checked in this study. Under optimized conditions, high concurrent production of xylanase (22,800 ± 578 IU/g substrate) and pectinase (4,832 ± 189 IU/g substrate) was achieved. The different types of pectinases produced were exo-polymethylgalacturonase (782 IU/g), endo-polymethylgalacturonase (6.42 U/g), exo-polygalacturonase (2,250 IU/g), endo-polygalacturonase (11.57 U/g), polymethylgalacturonate lyase (53.99 IU/g), polygalacturonate lyase (59.78 IU/g), and pectin esterase (5.78 IU/g). Wheat bran resulted in the highest titer of both enzymes. The maximum xylanase-pectinase yield was detected after 7 days of incubation with 2 mM MgSO₄ and 1.5 g/L K₂ HPO₄ at wheat bran to moisture ratio 1:1.5 (w/v), media to flask volume ratio 1:25, pH 7.0, temperature 37 °C, and inoculum size 15%. Xylanase was most stable at pH 8.0, retained more than 75% activity up to 24 H, whereas pectinase was most stable at pH 9.0, having full activity even after 24 H. At 45 °C, the xylanase showed 82% residual activity after 6 H of incubation. The pectinase was 97% and 61% stable up to 3 H at 50 and 55 °C, respectively. This is the first report showing the production of xylanase-pectinases by bacterium along with high titer of seven types of pectinases, suitable for industries.

The response surface optimization of β-mannanase produced by Lactobacillus casei HDS-01 and its potential in juice clarification

Lactic acid bacteria (LAB) is an ideal mannanase source due to the bio-safety guarantee. LAB can heterogeneously express β-mannanase or be directly used as β-mannanase-producing strains. This research originally optimized the fermentation condition for β-mannanase produced by Lactobacillus casei HDS-01. The applicable potential of the crude enzyme in juice clarification was investigated. Two-factorial design screened out three factors, i.e., fermentation time (p = 0.0001), glucose (p = 0.0013), and initial pH (p = 0.0167), which significantly affected L. casei HDS-01 β-mannanase activity. Under the predicted conditions resulting from the central composite design (CCD), i.e., fermentation time 18.23 hr, glucose 12.65 g L^-1, initial pH 5.18, the model reached maximal β-mannanase activity of 81.40 U mL^-1. This model was validated by conducting six repeated experiments and subsequent t-test (p = 0.6308). RSM optimization obtained a 1.33-fold increase in β-mannanase activity. This increase could also be qualitatively detected by larger clearance zone on konjac powder-MRS agar through Congo Red dyeing. The yield and clarity of crude β-mannanase-treated juices from orange, apple, and pear were significantly higher than controls without enzyme treatment. This study conferred a relatively high β-mannanase-producing LAB strain with a high bio-safety level and easy and economical use in juice clarification as well as other food-level fields.

Utility of acidic xylanase of Bacillus subtilis subsp. subtilis JJBS250 in improving the nutritional value of poultry feed

Cane molasses has been employed as a cost-effective medium for enhanced xylanase production in submerged fermentation. Bacillus subtilis subsp. subtilis JJBS250 produced xylanase (15.16 U/ml) at pH 4.0, 35 °C and 200 rpm after 54 h using optimized basal medium by 'one variable at a time approach'. Addition of Tween 80 and PEG 4000 also enhanced xylanase production in cane molasses medium. Combined effect of yeast extract, incubation time and PEG 4000 using statistical optimization enhanced xylanase production to 38.60 U/ml, which was 2.54-fold higher than the 'one variable at a time approach'. The efficacy of xylanase from Bacillus subtilis subsp. subtilis JJBS 250 was evaluated in the improvement of poultry feed nutrition. Xylanase addition (10 IU/g feed) enhanced liberation of reducing sugars (95.540 mg/g substrate) after 48 h at 60 °C. Optimization has resulted in enhanced production of xylanase that improved the nutritional quality of poultry feed.

Production optimization and characterization of mannooligosaccharide generating β-mannanase from Aspergillus oryzae

A multi-tolerant β-mannanase (ManAo) was produced by Aspergillus oryzae on copra meal, a low-cost agro waste. Under statistically optimized conditions, 4.3-fold increase in β-mannanase production (434 U/gds) was obtained. Purified ManAo had MW ∼34 kDa and specific activity of 335.85 U/mg with optimum activity at 60 °C and at pH 5.0. Activity of ManAo was enhanced by most metal ions and modulators while maximum enhancement was noticed with Ag⁺ and Triton X-100. K_m and V_max were 2.7 mg/mL and 1388.8 µmol/min/mg for locust bean gum while the enzyme showed lower affinity towards konjac gum (8.8 mg/mL, 555.5 µmol/min/mg). Evaluation of various thermodynamic parameters indicated high-efficiency of the ManAo with activation energy 12.42 KJ/mol and 23.31 KJ/mol towards LBG and konjac gum, respectively. End product analysis of β-mannanase action by fluorescence assisted carbohydrate electrophoresis (FACE) revealed the generation of sugars from DP 1-4 with some higher DP MOS from different mannans.

The composition of accessory enzymes of Penicillium chrysogenum P33 revealed by secretome and synergistic effects with commercial cellulase on lignocellulose hydrolysis

Herein, we report the secretome of Penicillium chrysogenum P33 under induction of lignocellulose for the first time. A total of 356 proteins were identified, including complete cellulases and numerous hemicellulases. Supplementing a commercial cellulase with increasing dosage of P33 enzyme cocktail from 1 to 5 mg/g substrate increased the release of reducing sugars from delignified corn stover by 21.4% to 106.8%. When 50% cellulase was replaced by P33 enzyme cocktail, release of reducing sugars was 78.6% higher than with cellulase alone. Meanwhile, glucan and xylan conversion was increased by 37% and 106%, respectively. P33 enzyme cocktail also enhanced commercial cellulase hydrolysis against four different delignified lignocellulosic biomass. These findings demonstrate that mixing appropriate amount of P33 cocktail with cellulase improves polysaccharide hydrolysis, suggesting P33 enzymes have great potential for industrial applications.

Production of proteases from organic wastes by solid-state fermentation: downstream and zero waste strategies

Production of enzymes through solid-state fermentation (SSF) of agro-industrial wastes reports high productivity with low investment. The extraction of the final product from the solid waste and solid disposal represent the main cost of the process. In this work, the complete downstream processes of SSF of two industrial residues for the production of proteases, soy fibre (SF) and a mixture of hair and sludge (HS), were studied in terms of activity recovery, using different extraction parameters (extracting solvent, ratio solid: solvent and extraction mode). Activity after lyophilisation was tested. Solid waste valorisation after extraction was studied using respiration techniques and biogas production tests, as part of a zero waste strategy. Results showed a maximum extraction yield of 91% for SF and 121% for HS, both in agitated mode and distilled water as extraction agent. An average activity recovery of 95 ± 6 and 94 ± 6% for SF and HS, respectively, was obtained after lyophilisation and redissolution. To reduce the cost of extraction, a ratio 1:3 w:v solid-solvent in static mode is advised for SF, and 1:2 w:v extraction ratio in agitated mode for HS, both with distilled water as extracting agent. Both composting and anaerobic digestion are suitable techniques for valorisation of the waste material.

Effect of the solid state fermentation of cocoa shell on the secondary metabolites, antioxidant activity, and fatty acids

During cocoa (Theobroma cacao L.) processing, the accumulated cocoa shell can be used for bioconversion to obtain valuable compounds. Here, we evaluate the effect of solid-state fermentation of cacao flour with Penicillium roqueforti on secondary metabolite composition, phenol, carotenoid, anthocyanin, flavonol, and fatty acids contents, and antioxidant activity. We found that the total concentrations of anthocyanins and flavonols did not change significantly after fermentation and the phenolic compound and total carotenoid concentrations were higher. The fermentation process produced an increase in saponin concentration and antioxidant activity, as well as significant changes in the levels of oleic, linoleic, gamma-linolenic, and saturated fatty acids. Based on our findings, we propose that the reuse of food residues through solid state fermentation is viable and useful.

A novel bifunctional acetyl xylan esterase/arabinofuranosidase from Penicillium chrysogenum P33 enhances enzymatic hydrolysis of lignocellulose

BACKGROUND

Xylan, the major constituent of hemicellulose, is composed of β-(1,4)-linked xylopyranosyl units that for the backbone, with side chains formed by other chemical moieties such as arabinose, galactose, mannose, ferulic acid and acetyl groups. Acetyl xylan esterases and α-L-arabinofuranosidases are two important accessory enzymes that remove side chain residues from xylan backbones and may act in synergy with other xylanolytic enzymes. Compared with enzymes possessing a single catalytic activity, multifunctional enzymes can achieve lignocellulosic biomass hydrolysis using a less complex mixture of enzymes.

RESULTS

Here, we cloned an acetyl xylan esterase (PcAxe) from Penicillium chrysogenum P33 and expressed it in Pichia pastoris GS115. The optimal pH and temperature of the recombinant PcAxe (rPcAxe) for 4-nitrophenyl acetate were 7.0 and 40 °C, respectively. rPcAxe is stable across a broad pH range, retaining 100% enzyme activity om pH 6-9 after a 1 h incubation. The enzyme tolerates the presence of a wide range of metal ions. Sequence alignment revealed a GH62 domain exhibiting α-L-arabinofuranosidase activity with pH and temperature optima of pH 7.0 and 50 °C, in addition to the expected esterase domain. rPcAxe displayed significant synergy with a recombinant xylanase, with a degree of synergy of 1.35 for the hydrolysis of delignified corn stover. Release of glucose was increased by 51% from delignified corn stover when 2 mg of a commercial cellulase was replaced by an equivalent amount of rPcAxe, indicating superior hydrolytic efficiency.

CONCLUSIONS

The novel bifunctional enzyme PcAxe was identified in P. chrysogenum P33. rPcAxe includes a carbohydrate esterase domain and a glycosyl hydrolase family 62 domain. This is the first detailed report on a novel bifunctional enzyme possessing acetyl xylan esterase and α-L-arabinofuranosidase activities. These findings expand our current knowledge of glycoside hydrolases and pave the way for the discovery of similar novel enzymes.

Effects of different cellulases on the release of phenolic acids from rice straw during saccharification

Effects of different cellulases on the release of phenolic acids from rice straw during saccharification were investigated in this study. All cellulases tested increased the contents of phenolic acids during saccharification. However, few free phenolic acids were detected, as they were present in conjugated form after saccharification when the cellulases from Trichoderma reesei, Trichoderma viride and Aspergillus niger were used. On the other hand, phenolic acids were present in free form when the Acremonium cellulolyticus cellulase was used. Assays of enzyme activity showed that, besides high cellulase activity, the A. cellulolyticus cellulase exhibited high feruloyl esterase (FAE) activity. A synergistic interaction between FAE and cellulase led to the increase in free phenolic acids, and thus an increase in antioxidative and antiradical activities of the phenolic acids. Moreover, a cost estimation demonstrated the feasibility of phenolic acids as value-added products to reduce the total production cost of ethanol.

Xylanase production by Aureobasidium pullulans on globe artichoke stem: Bioprocess optimization, enzyme characterization and application in saccharification of lignocellulosic biomass

Statistical optimization of the factors affecting xylanase production by Aureobasidium pullulans NRRL Y-2311-1 on globe artichoke stem was performed for the first time. The optimization strategies used resulted in almost six-fold enhancement of xylanase production (66.48 U/ml). Biochemical and thermal characterization of the crude xylanase preparation was performed to elucidate its feasibility for different industrial applications. The optimum conditions for xylanase activity were pH 4.0 and 30-50°C. The enzyme was very stable over a wide pH range of 3.0-8.0. The thermal stability studies revealed an inactivation energy of 183 kJ/mol. Thermodynamic parameters (enthalpy, entropy, and Gibbs free energy) for thermal inactivation were also determined. Primary application of the crude xylanase preparation in saccharification of corn cob subjected to different pretreatment techniques has been evaluated. The crude xylanase preparation was very promising for saccharification of corn cob pretreated with aqueous ammonia. The maximum yield of reducing sugar was 357 mg/g dry substrate, which revealed that the crude xylanase from A. pullulans could be a very good alternative in saccharification of lignocellulosic biomass for biological fuel generation. This study also provides a basis for further exploitation of globe artichoke by-products in microbial production of several other industrially significant metabolites.

Purification and characterization of β-mannanase from Aspergillus terreus and its applicability in depolymerization of mannans and saccharification of lignocellulosic biomass

Aspergillus terreus FBCC 1369 was grown in solid-state culture under statistically optimized conditions. β-Mannanase was purified to apparent homogeneity by ultrafiltration, anion exchange and gel filtration chromatography. A purification factor of 10.3-fold was achieved, with the purified enzyme exhibiting specific activity of 53 U/mg protein. The purified β-mannanase was optimally active at pH 7.0 and 70 °C and displayed stability over a broad pH range of 4.0–8.0 and a 30 min half-life at 80 °C. The molecular weight of β-mannanase was calculated as ~49 kDa by SDS-PAGE. The enzyme exhibited K_m and V_max values of 5.9 mg/ml and 39.42 µmol/ml/min, respectively. β-Mannanase activity was stimulated by β-mercaptoethanol and strongly inhibited by Hg²⁺. The β-Mannanase did not hydrolyze mannobiose and mannotriose, but only mannotetraose liberating mannose and mannotriose. This indicated that at least four mannose residues were required for catalytic activity. Oligosaccharide with a degree of polymerization (DP) three was the predominant product in the case of locust bean gum (16.5 %) and guar gum (15.8 %) hydrolysis. However, the enzyme liberated DP4 oligosaccharide (24 %) exclusively from konjac gum. This property can be exploited in oligosaccharides production with DP 3–4. β-Mannanase hydrolyzed pretreated lignocelluloses and liberated reducing sugars (% theoretical yield) from copra meal (30 %). This property is an important factor for the bioconversion of the biomass.

Bioconversion of lignocellulosic biomass to xylitol: An overview

Lignocellulosic wastes include agricultural and forest residues which are most promising alternative energy sources and serve as potential low cost raw materials that can be exploited to produce xylitol. The strong physical and chemical construction of lignocelluloses is a major constraint for the recovery of xylose. The large scale production of xylitol is attained by nickel catalyzed chemical process that is based on xylose hydrogenation, that requires purified xylose as raw substrate and the process requires high temperature and pressure that remains to be cost intensive and energy consuming. Therefore, there is a necessity to develop an integrated process for biotechnological conversion of lignocelluloses to xylitol and make the process economical. The present review confers about the pretreatment strategies that facilitate cellulose and hemicellulose acquiescent for hydrolysis. There is also an emphasis on various detoxification and fermentation methodologies including genetic engineering strategies for the efficient conversion of xylose to xylitol.