Spectrophotometric assay and electrophoretic detection of trans-feruloyl esterase activity.

Wheat bran cell walls were subjected to mild acid hydrolysis and the major phenolic product was purified and identified as 5-O-(trans-feruloyl)-arabinofuranose. Sensitive continuous and stopped, microtiter plate-based spectrophotometric assays for trans-feruloyl esterase activity were developed using this compound as substrate. Procedures were also developed for the detection of trans-feruloyl esterase activities on gels following electrophoresis using this compound. These procedures are applicable to other natural feruloyl esters derived from plant cell walls by enzymatic hydrolysis. The extracellular trans-feruloyl esterases of Aspergillus niger 814 grown on 1% wheat bran were fractionated by anion-exchange chromatography and isoelectric focusing. These studies indicate that there are multiple forms of trans-feruloyl esterase but that most activity is associated with a major isozyme with a pI of 3.2.     

Feruloyl esterase from aspergillus sp.: purification, properties, and action on natural substrates

An enzyme active toward the methyl ester of ferulic acid was isolated from the fungus Aspergillus sp. and purified to homogeneity using ion-exchange and hydrophobic chromatography. The molecular weight of the enzyme is 42 kD, and its pI is 3.7. The enzyme has a pH optimum in the range 4-6 and a temperature optimum in the range 40 to 60 degrees C. Using a number of synthetic and natural substrates, the enzyme was identified as a feruloyl esterase. The feruloyl esterase did not hydrolyze wheat straw. Ferulic acid was detected as a product of hydrolysis of wheat bran and sugar-beet pulp. Other products were also detected after sugar-beet pulp hydrolysis.     

Purification and characterization of an extracellular feruloyl esterase from the thermophilic anaerobe Clostridium stercorarium

Feruloyl esterases act as accessory enzymes for the complete saccharification of plant cell wall hemicelluloses. Although many fungal feruloyl esterases have been purified and characterized, few bacterial phenolic acid esterases have been characterized. This study shows the extracellular production of a feruloyl esterase by the thermophilic anaerobe Clostridium stercorarium when grown on birchwood xylan. The feruloyl esterase was purified 500-fold in successive steps involving ultrafiltration, preparative isoelectric focusing and column chromatography by anion exchange, gel filtration and hydrophobic interaction. The purified enzyme released ferulic, rho-coumaric, caffeic and sinapinic acid from the respective methyl esters. The purified enzyme also released ferulic acid from a de-starched wheat bran preparation. At pH 8.0 and 65 degrees C, the Km and Vmax values for the hydrolysis of methyl ferulate were 0.04 mmol l-l and 131 micromol min-1 mg-1, respectively; the respective values for methyl coumarate were 0.86 mmol l-l and 18 micromol min-1 mg-1. The purified feruloyl esterase had an apparent mass of 33 kDa under denaturing conditions and showed optimum activity at pH 8.0 and 65 degrees C. At a concentration of 5 mmol l-l, the ions Ca2+, Cu2+, Co2+ and Mn2+ reduced the activity by 70-80%.     

Purification and partial characterization of two feruloyl esterases from the anaerobic fungus Neocallimastix strain MC-2.

Two extracellular feruloyl esterases (FAE-I and FAE-II) produced by the anaerobic fungus Neocallimastix strain MC-2 which cleave ferulic acid from O-(5-O-[(E)-feruloyl]-alpha-L- arabinofuranosyl)-(1-->3)-O-beta-D-xylopyranosyl-(1-->4)-D-xylopyranose (FAXX) were purified. The molecular masses of FAE-I and FAE-II were 69 and 24 kDa, respectively, under both denaturing and nondenaturing conditions. Apparent Km and maximum rate of hydrolysis with FAXX were 31.9 microM and 2.9 mumol min-1 mg-1 for FAE-I and 9.6 microM and 11.4 mumol min-1 mg-1 for FAE-II. FAE-II was specific for FAXX, but FAE-I hydrolyzed FAXX and PAXX, the equivalent p-coumaroyl ester, at a maximum rate of metabolism ratio of 3:1.     

Feruloyl oligosaccharides stimulate the growth of Bifidobacterium bifidum

Insoluble dietary fiber from wheat bran contains some feruloyl groups linked to the arabinose residues in the cell wall arabinoxylan. Treatment of wheat bran insoluble dietary fiber with xylanase from Bacillus subtilis yielded feruloyl oligosacchairdes, which were purified with Amberlite XAD-2. Saponification of the feruloyl oligosaccharides released ferulic acid and arabinoxylan oligosaccharides which consist of arabinose and xylose. The effect of the feruloyl oligosacchairdes on the growth of Bifidobacterium bifidum F-35 was investigated in vitro. The B. bifidum produced acid when cultivated anaerobically in TPY broth with 0.5% feruloyl oligosacchairdes as the carbohydrate source. The biomass yield of the B. bifidum increased with increasing the concentration of feruloyl oligosaccharides in TPY broth. The maximum cell growth was increased by 50% in TPY broth supplemented with 0.1% feruloyl oligosaccharides compared to TPY broth. These results indicated that the growth of B. bifidum F-35 was promoted by the feruloyl oligosaccharides from wheat bran insoluble dietary fiber, and not suppressed by the ferulic acid moiety of them.     

Sulfated and pyruvylated disaccharide alditols obtained from a red seaweed galactan: ESIMS and NMR approaches

The water-soluble acid agaran isolated from Acanthophora spicifera (Rhodophyta) was submitted to alkaline treatment for the complete cyclization of alpha-L-Galp 6-sulfate to 3,6-An-alpha-L-Galp units. The modified agaran was then partially depolymerized using partial reductive hydrolysis. The resulting oligosaccharide mixture was fractionated by adsorption and ion-exchange chromatography. Fractions were purified by gel-filtration chromatography and studied by ESIMS and NMR spectroscopy, including 1D 1H, 13C, DEPT and 2D 1H, 1H COSY, TOCSY and 1H, 13C HMQC procedures. The following neutral, pyruvylated, sulfated and sulfated/pyruvylated disaccharide alditols were obtained: beta-D-Galp-(1-->4)-3,6-An-L-GalOH; 4,6-O-(1-carboxyethylidene)-beta-D-Galp-(1-->4)-3,6-An-L-GalOH; beta-D-Galp 2-sulfate-(1-->4)-3,6-An-L-GalOH and 4,6-O-(1-carboxyethylidene)-beta-D-Galp 2-sulfate-(1-->4)-3,6-An-L-GalOH.     

Purification and characterization of a feruloyl esterase from Fusarium oxysporum catalyzing esterification of phenolic acids in ternary water-organic solvent mixtures

An extracellular feruloyl esterase (FAE-II) from the culture filtrates of Fusarium oxysporum F3 was purified to homogeneity by SP-Sepharose, t-butyl-HIC and Sephacryl S-200 column chromatography. The protein corresponded to molecular mass and pI values of 27 kDa and 9.9, respectively. The enzyme was optimally active at pH 7 and 45 degrees C. The purified esterase was fully stable at pH 7.0-9.0 and temperature up to 45 degrees C after 1 h incubation. Determination of k(cat)/K(m) revealed that the enzyme hydrolysed methyl sinapinate 6, 21 and 40 times more efficiently than methyl ferulate, methyl coumarate and methyl caffeate, respectively. The enzyme was active on substrates containing ferulic acid ester linked to the C-5 but inactive to the C-2 positions of arabinofuranose such as 4-nitrophenyl 5-O-trans-feruloyl-alpha-L-arabinofuranoside and 4-nitrophenyl 2-O-trans-feruloyl-alpha-L-arabinofuranoside. In the presence of Sporotrichum thermophile xylanase, there was a significant release of ferulic acid from destarched wheat bran by FAE-II, indicating a synergistic interaction between FAE-II and S. thermophile xylanase. FAE-II by itself could release only little ferulic acid from destarched wheat bran. The potential of FAE-II for the synthesis of various phenolic acid esters was tested using as a reaction system a surfactantless microemulsion formed in ternary mixture consisting of n-hexane, 1-propanol and water.     

The wood rot ascomycete Xylaria polymorpha produces a novel GH78 glycoside hydrolase that exhibits α-L-rhamnosidase and feruloyl esterase activities and releases hydroxycinnamic acids from lignocelluloses

Soft rot (type II) fungi belonging to the family Xylariaceae are known to substantially degrade hardwood by means of their poorly understood lignocellulolytic system, which comprises various hydrolases, including feruloyl esterases and laccase. In the present study, several members of the Xylariaceae were found to exhibit high feruloyl esterase activity during growth on lignocellulosic materials such as wheat straw (up to 1,675 mU g(-1)) or beech wood (up to 80 mU g(-1)). Following the ester-cleaving activity toward methyl ferulate, a hydrolase of Xylaria polymorpha was produced in solid-state culture on wheat straw and purified by different steps of anion-exchange and size-exclusion chromatography to apparent homogeneity (specific activity, 2.2 U mg(-1)). The peptide sequence of the purified protein deduced from the gene sequence and verified by de novo peptide sequencing shows high similarity to putative α-L-rhamnosidase sequences belonging to the glycoside hydrolase family 78 (GH78; classified under EC 3.2.1.40). The purified enzyme (98 kDa by SDS-PAGE, 103 kDa by size-exclusion chromatography; pI 3.7) converted diverse glycosides (e.g., α-L-rhamnopyranoside and α-L-arabinofuranoside) but also natural and synthetic esters (e.g., chlorogenic acid, hydroxycinnamic acid glycoside esters, veratric acid esters, or p-nitrophenyl acetate) and released free hydroxycinnamic acids (ferulic and coumaric acid) from arabinoxylan and milled wheat straw. These catalytic properties strongly suggest that X. polymorpha GH78 is a multifunctional enzyme. It is the first fungal enzyme that combines glycosyl hydrolase with esterase activities and may help this soft rot fungus to degrade lignocelluloses.     

Utilization of agro-industrial waste for xylanase production by Aspergillus foetidus MTCC 4898 under solid state fermentation and its application in saccharification

Xylanase production by Aspergillus foetidus MTCC 4898 was carried out under solid state fermentation using wheat bran and anaerobically treated distillery spent wash. Response surface methodology involving Box–Behnken design was employed for optimizing xylanase production. The interactions among various fermentation parameters viz. moisture to substrate ratio, inoculum size, initial pH, effluent concentration and incubation time were investigated and modeled. The predicted xylanase activity under optimized parameters was 8200–8400 U/g and validated xylanase activity was 8450 U/g with very poor cellulase activity. Crude xylanase was used for enzymatic saccharification of agroresidues like wheat straw, rice straw and corncobs. Dilute NaOH and ammonia pretreatments were found to be beneficial for the efficient enzymatic hydrolysis of all the three substrates. Dilute NaOH pretreated wheat straw, rice straw and corncobs yielded 4, 4.2, 4.6 g/l reducing sugars, respectively whereas ammonia treated wheat straw, rice straw and corncobs yielded 4.9, 4.7, 4.6 g/l reducing sugars, respectively. The hydrolyzates were analysed by HPTLC. Xylose was found to be the major end product with traces of glucose in the enzymatic hydrolyzates of all the substrates.     

Purification and characterization of a feruloyl esterase from the intestinal bacterium Lactobacillus acidophilus

Dietary ferulic acid (FA), a significant antioxidant substance, is currently the subject of extensive research. FA in cereals exists mainly as feruloylated sugar ester. To release FA from food matrices, it is necessary to cleave ester cross-linking by feruloyl esterase (FAE) (hydroxycinnamoyl esterase; EC 3.1.1.73). In the present study, the FAE from a human typical intestinal bacterium, Lactobacillus acidophilus, was isolated, purified, and characterized for the first time. The enzyme was purified in successive steps including hydrophobic interaction chromatography and anion-exchange chromatography. The purified FAE appeared as a single band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, with an apparent molecular mass of 36 kDa. It has optimum pH and temperature characteristics (5.6 and 37 degrees C, respectively). The metal ions Cu(2+) and Fe(3+) (at a concentration of 5 mmol liter(-1)) inhibited FAE activity by 97.25 and 94.80%, respectively. Under optimum pH and temperature with 5-O-feruloyl-L-arabinofuranose (FAA) as a substrate, the enzyme exhibited a K(m) of 0.0953 mmol liter(-1) and a V(max) of 86.27 mmol liter(-1) min(-1) mg(-1) of protein. Furthermore, the N-terminal amino acid sequence of the purified FAE was found to be A R V E K P R K V I L V G D G A V G S T. The FAE released FA from O-(5-O-feruloyl-alpha-L-arabinofuranosyl)-(1-->3)-O-beta-D-xylopyranosyl-(1-->4)-D-xylopyranose (FAXX) and FAA obtained from refined corn bran. Moreover, it released two times more FA from FAXX in the presence of added xylanase.     

Transglycosylation to ginseng saponins by cyclomaltodextrin glucanotransferases

Ten new alpha-glucosylginsenosides were found to be synthesized from dextrin and four ginsenosides, -Rb1, -Rc, -Re, and -Rg1, by the successive actions of B. stearothermophilus cyclomaltodextrin glucanotransferase and Rhizopus glucoamylase. Seven of them were isolated in the pure state by extraction with n-butanol saturated with water, silica gel column chromatography, and high pressure liquid chromatography, and identified as 3-O-[alpha-D-glcp-(1-->4)-beta-D-glcp-(1-->2)-beta-D-glcp]-20-O-[beta-D-glcp-(1-->6)-beta-D-glcp]-20(S)-protopanaxadiol, 3-O-[beta-D-glcp-(1-->2)-beta-D-glcp]-20-O-[alpha-D-glcp-(1-->4)-beta-D-glcp-(1-->6)-beta-D-glcp]-20(S)-protopanaxadiol, 3-O-[alpha-D-glcp-(1-->4)-beta-D-glcp-(1-->2)-beta-D-glcp]-20-O-[alpha-L-araf-(1-->6)-beta-D-glcp]-20(S)-protopanaxadiol, 3-O-[beta-D-glcp-(1-->2)-beta-D-glcp]-20-O-[(4G-alpha-D-glcp)-alpha-L-araf-(1-->6)-beta-D-glcp]-20(S)-protopanaxadiol, 6-O-[alpha-L-rhap-(1-->2)-beta-D-glcp]-20-O-[alpha-D-glcp-(1-->4)-beta-D-glcp]-20(S)-protopanaxatriol, 6-O-[alpha-D-glcp-(1-->4)-beta-D-glcp]-20-O-(beta-D-glcp)-20(S)-protopanaxatriol, and 6-O-[alpha-D-glcp-(1-->3)-beta-D-glcp]-20-O-(beta-D-glcp)-20(S)-protopanaxatriol, by spectroscopy (FAB-MS, IR, 1H-NMR and 13C-NMR) and hydrolysis products in 50% acetic acid. The bitterness of these alpha-glucosyl-ginsenosides was less than that of ginsenosides.     

Feruloyl esterases as a tool for the release of phenolic compounds from agro-industrial by-products

Agro-industrial by-products are a potential source of added-value phenolic acids with promising applications in the food and pharmaceutical industries. Here two purified feruloyl esterases from Aspergillus niger, FAEA and FAEB were tested for their ability to release phenolic acids such as caffeic acid, p-coumaric acid and ferulic acid from coffee pulp, apple marc and wheat straw. Their hydrolysis activity was evaluated and compared with their action on maize bran and sugar beet pulp. The specificity of both enzymes against natural and synthetic substrates was evaluated; particular attention was paid to quinic esters and lignin monomers. The efficiency of both enzymes on model substrates was studied. We show the ability of these enzymes to hydrolyze quinic esters and ester linkages between phenolic acids and lignin monomer.     

A halotolerant type A feruloyl esterase from Pleurotus eryngii

An extracellular feruloyl esterase (PeFaeA) from the culture supernatant of Pleurotus eryngii was purified to homogeneity using cation exchange, hydrophobic interaction, and size exclusion chromatography. The length of the complete coding sequence of PeFaeA was determined to 1668 bp corresponding to a protein of 555 amino acids. The catalytic triad of Ser-Glu-His demonstrated the uniqueness of the enzyme compared to previously published FAEs. The purified PeFaeA was a monomer with an estimated molecular mass of 67 kDa. Maximum feruloyl esterase (FAE) activity was observed at pH 5.0 and 50 °C, respectively. Metal ions (5 mM), except Hg²⁺, had no significant influence on the enzyme activity. Substrate specificity profiling characterized the enzyme as a type A FAE preferring bulky natural substrates, such as feruloylated saccharides, rather than small synthetic ones. K_m and k_cat of the purified enzyme for methyl ferulate were 0.15 mM and 0.85 s⁻¹. In the presence of 3 M NaCl activity of the enzyme increased by 28 %. PeFaeA alone released only little ferulic acid from destarched wheat bran (DSWB), whereas after addition of Trichoderma viride xylanase the concentration increased more than 20 fold.     

Purification and partial characterization of two feruloyl esterases from the anaerobic fungus Neocallimastix strain MC-2.

Two extracellular feruloyl esterases (FAE-I and FAE-II) produced by the anaerobic fungus Neocallimastix strain MC-2 which cleave ferulic acid from O-(5-O-[(E)-feruloyl]-alpha-L- arabinofuranosyl)-(1-->3)-O-beta-D-xylopyranosyl-(1-->4)-D-xylopyranose (FAXX) were purified. The molecular masses of FAE-I and FAE-II were 69 and 24 kDa, respectively, under both denaturing and nondenaturing conditions. Apparent Km and maximum rate of hydrolysis with FAXX were 31.9 microM and 2.9 mumol min-1 mg-1 for FAE-I and 9.6 microM and 11.4 mumol min-1 mg-1 for FAE-II. FAE-II was specific for FAXX, but FAE-I hydrolyzed FAXX and PAXX, the equivalent p-coumaroyl ester, at a maximum rate of metabolism ratio of 3:1.     

Production of xylanase under solid-state fermentation by <Emphasis Type="Italic">Aspergillus tubingensis</Emphasis> JP-1 and its application

The production of extracellular xylanase by a locally isolated strain of Aspergillus tubingensis JP-1 was studied under solid-state fermentation. Among the various agro residues used wheat straw was found to be the best for high yield of xylanase with poor cellulase production. The influence of various parameters such as initial pH, moisture, moistening agents, nitrogen sources, additives, surfactants and pretreatment of substrates were investigated. The production of the xylanase reached a peak in 8 days using untreated wheat straw with modified MS medium, pH 6.0 at 1:5 moisture level at 30 °C. Under optimized conditions yield as high as 6,887 ± 16 U/g of untreated wheat straw was achieved. Crude xylanase was used for enzymatic saccharification of agro-residues like wheat straw, rice bran, wheat bran, sugarcane bagasse and industrial paper pulp. Dilute alkali (1 N NaOH) and acid (1 N H₂SO₄) pretreatment were found to be beneficial for the efficient enzymatic hydrolysis of wheat straw. Dilute alkali and acid-pretreated wheat straw yielded 688 and 543 mg/g reducing sugar, respectively. Yield of 726 mg/g reducing sugar was obtained from paper pulp after 48 h of incubation.     

Comparison of Feedstock Pretreatment Performance and Its Effect on Soluble Sugar Availability

Cellulosic feedstocks for bioenergy differ in composition and processing requirements for efficient conversion to chemicals and fuels. This study discusses and compares the processing requirements for three lignocellulosic feedstocks??soybean hulls, wheat straw, and de-starched wheat bran. They were ground with a hammer mill to investigate how differences in composition and particle size affect the hydrolysis process. Enzyme hydrolysis was conducted using cellulase from Trichoderma reesei at 50°C and pH 5. Ground fractions were also subjected to dilute sulfuric acid treatment at 125°C, 15 psi for 30 min prior to cellulase treatment. Reducing particle size of biomass resulted in segregated components of feedstock. Grinding wheat straw to particle size <132 ??m resulted in measured lignin content from 20% to ??5% and reduced hemicellulose content. Reducing lignin content increased the effectiveness of enzyme hydrolysis of wheat straw. Particles sized <132 ??m exhibited the highest soluble sugar release upon hydrolysis for all three feedstocks studied. Hemicellulose digestion improved with dilute sulfuric acid treatment with residual hemicellulose content <5% in all three feedstocks after acid treatment. This enhanced the cellulase action and resulted in approximately 1.6-fold increase in sugar availability in de-starched wheat bran and ??1.5-fold for wheat straw and soybean hulls. Higher sugar availability in wheat bran after acid-mediated enzyme treatment correlated to higher ethanol yields during yeast fermentation compared with soybean hulls and wheat straw.     

Monosaccharide yields and lignin removal from wheat straw in response to catalyst type and pH during mild thermal pretreatment

The influence of various low temperature (140 °C) pretreatments, using different acid and alkaline catalysts and different pH values, was studied for enzymatic hydrolysis of wheat straw. The pretreated wheat straw was treated by a standard blend of Celluclast 1.5L and Novozym 188. While pretreatment at pH 1 gave the highest yield of saccharides in the liquid fraction, the solid fraction was more susceptible to enzymatic attack when pretreated at pH 13. The highest yields were obtained after pretreatment with hydrochloric acid at pH 1, and with sodium hydroxide at pH 13 when enzymatic hydrolysis was employed. A two-step pretreatment strategy at pH 1 (hydrochloric acid) and subsequently at pH 13 (sodium hydroxide) released 69% and 95% of the theoretical maximal amounts of glucose and xylose, respectively. Furthermore, this two-step pretreatment removed 68% of the lignin from the straw with only minor losses of monosaccharides and production of only low amounts of inhibitors. Type of catalyst and pH indeed influenced the monosaccharide yields and lignin removal from wheat straw, and need more attention in the choice of pretreatment strategy.     

Sporotrichum thermophile type C feruloyl esterase (StFaeC): purification,characterization, and its use for phenolic acid (sugar) ester synthesis

A feruloyl esterase (StFaeC) produced by Sporotrichum thermophile was purified to homogeneity. The native StFaeC was homodimer with a subunit of M_r 23,000 and pI 3.1. The enzyme activity was optimal at pH 6.0 and 55 °C. The esterase displayed remarkable stability at pH 10.0 and retained 50% of its activity after 133 and 55 min at 55 and 60 °C, respectively. Determination of k_cat/K_m revealed that the enzyme had a broad spectrum of activity against the (hydroxyl) cinnamate esters indicating a type C feruloyl esterase. The enzyme was active on substrates containing ferulic acid ester linked to the C-5 and C-2 linkages of arabinofuranose and hydrolysed 4-nitrophenyl-5-O-trans-feruloyl-α-l-arabinofuranoside three times more efficiently than 4-nitrophenyl-2-O-trans-feruloyl-α-l-arabinofuranoside. Ferulic acid was efficiently released from wheat bran when the esterase was incubated together with xylanase from S. thermophile (a maximum of 41% total ferulic acid released after 1 h incubation). StFaeC by itself could release FA but at a level almost 10-fold lower than that obtained in the presence of xylanase. The potential of StFaeC for the synthesis of various phenolic acid esters was examined using as a reaction system a ternary water–organic mixture consisting of n-hexane, 1-butanol and water. Also StFaeC catalyzed the transfer of the feruloyl group to l-arabinose in a similar system using t-butanol, with about a 40% conversion of l-arabinose to feruloylated derivative was achieved. This work is the first example of enzymatic feruloylation of a carbohydrate.     

Purification and characterization of a feruloyl esterase from the fungus Penicilliumexpansum

An extracellular phenolic acid esterase produced by the fungus Penicillium expansum in solid state culture released ferulic and ρ-coumaric acid from methyl esters of theacids, and from the phenolic-carbohydrate esters O-[5-O-(trans-feruloyl)-α- l -arabinofuranosyl]-(1 → 3)-O-β- d -xylopyranosyl-(1 → 4)- d -xylopyranose (FAXX) and O-[5-O-((E)-ρ-coumaroyl)-α- l -arabinofuranosyl]-(1 → 3)-O-β- d -xylopyranosyl-(1 → 4)- d -xylopyranose(PAXX). The esterase was purified 360-fold in successive stepsinvolving ultrafiltration and column chromatography by gel filtration, anion exchange andhydrophobic interaction. These chromatographic methods separated the phenolic acid esterasefrom α- l -arabinofuranosidase, pectate and pectin lyase, polygalacturonase,xylanase and β- d -xylosidase activities. The phenolic acid esterase had an apparentmass of 65 kDa under non-denaturing conditions and a mass of 57·5 kDa underdenaturing conditions. Optimal pH and temperature were 5·6 and 37 °C,respectively and the metal ions Cu2+ and Fe³+ atconcentrations of 5 mmol l⁻¹ inhibited feruloyl esterase activity by 95% and44%, respectively, at the optimum pH and temperature. The apparent K_m and V_max of the purified feruloyl esterase for methyl ferulate at pH 5·6 and 37 °Cwere 2·6 mmol l⁻¹ and 27·1 μmol min⁻¹ mg⁻¹. The corresponding constants of ρ-coumaroylesterase for methyl coumarate were 2·9 mmol l⁻¹ and 18·6μmol min−1 mg⁻¹.     

Isolation and partial characterization of alkaline feruloyl esterases from Aspergillus niger CFR 1105 grown on wheat bran

Feruloyl esterases (FAEs) of a strain of Aspergillus niger (CFR 1105) grown in solid state (ssf) and submerged fermentations (smf) using wheat bran both as carbon source and inducer of the enzyme were studied. The feruloyl esterase activity was maximum after 4 days in solid state as well as in submerged fermentations (32.5 and 31.5 U/g dry weight of wheat bran respectively) and the enzyme titers were comparable. The specific activity was maximum on day 2 in ssf (12.8 U/mg protein) and it decreased thereafter, whereas specific activity was maximum on day 3 (11.7 U/mg protein) in smf and it remained constant up to 5 days. Two isoenzymes of feruloyl esterases were isolated and purified to homogeneity by conventional protein purification methods from the day 5 culture filtrate of A. niger grown in smf. On a DEAE-cellulose column, two enzyme activity peaks designated as FAE-1 and FAE-2 were eluted with 0.3 and 0.35 M NaCl, respectively. They were monomeric glycoproteins with approximate molecular weights of 50 kDa (FAE-1) and 55 kDa (FAE-2), respectively. FAE-1 showed a temperature optimum of 40°C whereas FAE-2 showed a wider temperature optimum of 40–50°C. FAE-1 and FAE-2 exhibited pH optima of 9 and 6, respectively, and both were stable over a pH range of 6–9. The ability of the enzyme to be active in alkaline pH may be advantageous in biotechnological applications.