Eco-friendly processing in enzymatic xylooligosaccharides production from corncob: Influence of pretreatment with sonocatalytic-synergistic Fenton reaction and its antioxidant potentials

Are phenolic compounds produced during the enzymatic production of prebiotic xylooligosaccharides (XOS) beneficial: a review

Phenolics produced during xylooligosaccharide production might inhibit xylanases and enhance the antioxidant and antimicrobial activities of XOS. The effects of phenolic compounds on xylanases may depend on the type and concentration of the compound, the plant biomass used, and the enzyme used. Understanding the effects of phenolic compounds on xylanases and their impact on XOS is critical for developing viable bioconversion of lignocellulosic biomass to XOS. Understanding the complex relationship between phenolic compounds and xylanases can lead to the development of strategies that improve the efficiency and cost-effectiveness of XOS manufacturing processes and optimise enzyme performance.

Antioxidant capacity of xylooligosaccharides generated from beechwood xylan by recombinant family GH10 Aspergillus niger xylanase A and insights into the enzyme's competitive inhibition by riceXIP

In this study, the family GH10 xylanase AnXylA10 derived from Aspergillus niger JL15 strain was expressed in Pichia pastoris X33. The recombinant xylanase, reAnXylA10 exhibited optimal activity at 40 ℃ and pH 5.0. The hydrolysates generated from beechwood xylan using reAnXylA10 primarily consisted of xylobiose (X2) to xylohexaose (X6) and demonstrated remarkable antioxidant capacity. Furthermore, the rice xylanase inhibitory protein (riceXIP) was observed to competitively inhibit reAnXylA10, exhibiting an inhibition constant (Ki) of 140.6 nM. Molecular dynamics (MD) simulations of AnXylA10-riceXIP complex revealed that the α-7 helix (Q225-S238) of riceXIP intruded into the catalytic pocket of AnXylA10, thereby obstructing substrate access to the active site. Specifically, residue K226 of riceXIP formed robust interactions with E136 and E242, the two catalytic sites of AnXylA10, predominantly through high-occupied hydrogen bonds. Based on QTAIM, electron densities for the atom pairs K226riceXIP@HZ1-E136AnXylA10@OE2 and K226riceXIP@HZ3-E242AnXylA10@OE1 were determined to be 0.04628 and 0.02914 a.u., respectively. Binding free energy of AnXylA10-riceXIP complex was -59.0±7.6 kcal/mol, significantly driven by electrostatic and van der Waals forces. Gaining insights into the interaction between xylanase and its inhibitors, and mining the inhibition mechanism in depth, will facilitate the design of innovative GH10 family xylanases that are both highly efficient and resistant to inhibitors.

Xylooligosaccharides produced from sugarcane leaf arabinoxylan using xylanase from Aureobasidium pullulans NRRL 58523 and its prebiotic activity toward Lactobacillus spp

In an attempt to enhance the value of sugarcane leaf, xylan was extracted and used for xylooligosaccharide (XO) production via enzymatic hydrolysis using xylanase from the black yeast Aureobasidium pullulans. The xylan was extracted from sugarcane leaf using alkali extraction according to the response surface methodology. The highest xylan yield (99.42 ± 4.05 % recovery) was obtained using 14.32 % (w/v) NaOH, 13.25:1 liquid: solid ratio, at 121 °C and 15 lb.in2 for 32 min. Sugar composition and FTIR spectrum analyses confirmed its structure as arabinoxylan. The extracted arabinoxylan had a relatively high molecular weight compared to previous studies. Crude endoxylanase from A. pullulans NRRL 58523 was selected for enzymatic hydrolysis of the xylan. The enzyme hydrolyzed well at 50 °C, pH 4.0 and was relatively stable under this condition (87.38 ± 1.26 % of the activity remained after 60 h). XOs, especially xylobiose and xylotriose, were obtained at the maximum yield of 237.51 ± 17.69 mg/g xylan via endoxylanase hydrolysis under the optimum conditions (50 °C, pH 4.0, 65.31 U/g xylan, 53 h). XOs exhibited species-specific prebiotic activity toward three strains of Lactobacillus spp. but not toward Bifidobacterium spp.

Preparation and characterization of cellulose nanocrystals from corncob via ionic liquid [Bmim][HSO4] hydrolysis: effects of major process conditions on dimensions of the product

In this study, cellulose nanocrystals were prepared via the hydrolysis of corncob (CC) biomass using Brønsted acid ionic liquid 1-butyl-3-methylimidazolium hydrogen sulfate [Bmim][HSO₄]. The corncob was subjected to alkaline pretreatment, and was then hydrolysed by [Bmim][HSO₄], which acted as both solvent and catalyst. The effects of process conditions, including mass percent of CC (1.0-10.0%), reaction temperature (46-110 °C), and reaction time (1.2-2.8 h) on the size of cellulose nanocrystals (IL-CCCNC) were investigated by response surface methodology-central composite design. The obtained IL-CCCNC was characterized by Fourier transforms infrared spectroscopy, zeta sizer, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and thermogravimetry. The results showed that the dimensions of the nanocellulose products were affected by the mass percent of CC and the reaction temperature, but were not significantly influenced by the reaction time under the studied conditions. The optimal conditions, estimated by the developed model, were a mass percent of 2.49%, reaction temperature of 100 °C, and reaction time of 1.5 h. The process successfully produced IL-CCCNC with a yield of 40.13%, average size of 166 nm, and crystallinity index (CrI) of 62.5%. The morphology, chemical fingerprints, and thermal properties of the obtained IL-CCCNC were comparable to those extracted by alkaline and acid hydrolysis. After the reaction, [Bmim][HSO₄] could be recovered with a yield of 88.32%, making it a viable green catalyst for the hydrolysis of CC cellulose. The findings are of direct industrial relevance as optimal processes can be developed to produce nanocellulose crystals with desirable size and physicochemical characteristics.

A New Insight into the Composition and Physical Characteristics of Corncob—Substantiating Its Potential for Tailored Biorefinery Objectives

Corncobs of four different corn varieties were physically segregated into two different anatomical portions, namely the corncob outer (CO) and corncob pith (CP). The biomass composition analysis of both the CO and CP was performed by four different methods. The CP showed a higher carbohydrate and lower lignin content (83.32% and 13.58%, respectively) compared with the CO (79.93% and 17.12%, respectively) in all of the methods. The syringyl/guaiacyl (S/G) ratio was observed to be higher in the CP (1.34) than in the CO (1.28). The comprehensive physical characterization of both samples substantiated the lower crystallinity and lower thermal stability that was observed in the CP compared to the CO. These properties make the CP more susceptible to glycanases, as evident from the enzymatic saccharification of CP carried out with a commercial cellulase and xylanase in this work. The yields obtained were 70.57% and 88.70% of the respective theoretical yields and were found to be equal to that of pure cellulose and xylan substrates. These results support the feasibility of the tailored valorization of corncob anatomical portions, such as enzymatic production of xylooligosaccharides from CP without pretreatment combined with the bioethanol production from pretreated CO to achieve an economical biorefinery output from corncob feedstock.

Preparation and nutritional properties of xylooligosaccharide from agricultural and forestry byproducts: A comprehensive review

Xylooligosaccharide (XOS) are functional oligosaccharides with prebiotic activities, which originate from lignocellulosic biomass and have attracted extensive attention from scholars in recent years. This paper summarizes the strategies used in the production of XOS, and introduces the raw materials, preparation methods, and purification technology of XOS. In addition, the biological characteristics and applications of XOS are also presented. The most commonly recommended XOS production strategy is the two-stage method of alkaline pre-treatment and enzymatic hydrolysis; and further purification by membrane filtration to achieve the high yield of XOS is required for prebiotic function. At the same time, new strategies and technologies such as the hydrothermal and steam explosion have been used as pre-treatment methods combined with enzymatic hydrolysis to prepare XOS. XOS have many critical physiological activities, especially in regulating blood glucose, reducing blood lipid, and improving the structure of host intestinal flora.

Two-step acetic acid/sodium acetate and xylanase hydrolysis for xylooligosaccharides production from corncob

At present, xylooligosaccharides (XOS) from corncob using acid-base conjugate system has not been reported. In this study, XOS production from corncob by two-step acetic acid/sodium acetate (AC/SA) conjugate system hydrolysis and xylanase hydrolysis was optimized, and monosaccharides were subsequently produced from corncob residues by cellulase hydrolysis. The XOS of 19.9 g/L was obtained from corncob (10%, w/v) using 0.15 M AC/SA hydrolysis at a molar ratio of 3.0 at 170 °C for 60 min, followed by xylanase hydrolysis. The second-step AC/SA hydrolysis of hydrolyzed corncob (10%, w/v) produced 3.1 g/L of XOS. Finally, the maximum XOS yield of 74.8% (based on xylan in corncob) was achieved, which is the highest yield among yields reported previously. The purity of XOS was high, whereas the contents of by-products were very low. This work presents a novel and promising strategy for co-production of XOS and monosaccharides from corncob without xylan isolation and purification.

Production and characterization of functional wheat bran hydrolysate rich in reducing sugars, xylooligosaccharides and phenolic acids

The aim was to enhance production of functional hydrolysate from wheat bran (WB). WB was hydrolyzed with 3000 U/mL ɑ-amylase and 1200 U/mL alkaline protease to prepare WB insoluble dietary fibre (WBIDF). Functional hydrolysate production from the extract containing crude xylan of WBIDF by xylanase was optimized by Taguchi method. The optimal condition for xylan degradation and functional substances production was 78.50 U/mL xylanase, pH 10.0, 50 °C, and reaction time 6 h. The maximum yield of reducing sugars was 614.0 μg/mL, xylobiose increased from 12.9 μg/mL to 213.3 μg/mL, xylotriose increased from 34.9 μg/mL to 174.0 μg/mL, ferulic acid 13.1 μg/mL made up 57.5 % of the total identifiable phenolic pool in the hydrolysate. The total antioxidant activity of hydrolysate was 141.8 mg ascorbic acid equivalents g^-1 crude xylan, and the highest 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity reached 92.7 %. The hydrolysate exhibited great potential in agricultural and food industry application.

Chemical-free and synergistic interaction of ultrasound combined with plasma-activated water (PAW) to enhance microbial inactivation in chicken meat and skin

In general, the poultry industry uses 0.5–1 ppm chlorine solution in the meat sanitization process. However, chlorine can react with organic material and produce halogenated organic compounds, notably chloroform, which causes bladder and rectal cancer in humans. For this reason, many industries try to avoid chlorine. This study investigated the efficacy of ultrasound and plasma-activated water (PAW) on the inactivation of Escherichia coli and Staphylococcus aureus in chicken muscle, rough skin, and smooth skin. Samples inoculated with bacteria suspension were treated by ultrasound alone and PAW–ultrasound. The Taguchi method and desirability function approach were used for the experimental design and optimization. Combined ultrasound and PAW inactivated up to 1.33 log CFU/ml of E. coli K12 and 0.83 log CFU/ml of S. aureus at a sample thickness of 4 mm, at 40 °C for 60 min, while PAW alone only reduced E. coli K12 by 0.46 log CFU/ml and S. aureus by 0.33 log CFU/ml under the same condition. The muscle topography showed a porous structure, which facilitated the penetration of PAW. The color measurements of muscle treated with ultrasound and PAW–ultrasound were dramatically different from the untreated sample, as also perceived by the sensory evaluation panel. Therefore, the synergistic interaction of combined PAW–ultrasound could be used to enhance microbial inactivation in meat.

Differential inhibition of GH family 11 endo-xylanase by rice xylanase inhibitor and verification by a modified yeast two-hybrid system

Rice xylanase inhibitor (RIXI) is a XIP-type xylanase inhibitor protein that protects rice cells from pathogenic organisms. RIXI inhibits most microbial xylanases and thus decreases their practical application. The recombinant RIXI (rePRIXI) showed evident inhibitory activities against several family 11 endo-xylanases. After interaction with rePRIXI at 50 °C for 40 min, the residual activities of reBaxA50, reBaxA, TfxA_CD214, and TfxA_CD were 55.6%, 30.3%, 30.09%, and 11.20%, respectively. Intrinsic fluorescence of reBaxA50 and TfxA_CD214 was statically quenched after interaction with rePRIXI. rePRIXI decreased hydrolysis of beechwood xylan by reBaxA50 and TfxA_CD214. Molecular dynamics simulations revealed the long loop (residues 144-153) of RIXI inserts into the catalytic cleft of family 11 xylanases. Native PAGE results revealed the formation of RIXI-xylanase complex after their interaction in the test tube. Interactions were also observed between RIXI and xylanases in living yeast cells. The results of inhibitory activity assay and modified yeast two-hybrid revealed that the inhibitory activity of RIXI on family 11 xylanase improved with the interaction strength of the RIXI-xylanase complex, indicating their positive correlation. The modified yeast two-hybrid system is relatively simple and has low cost, and its use may be extended to other studies on protein-protein interactions.

Efficient pretreatment of lignocellulosic biomass with high recovery of solid lignin and fermentable sugars using Fenton reaction in a mixed solvent

BACKGROUND

Pretreatment of biomass to maximize the recovery of fermentable sugars as well as to minimize the amount of enzyme inhibitors formed during the pretreatment is a challenge in biofuel process. We develop a modified Fenton pretreatment in a mixed solvent (water/DMSO) to combine the advantages of organosolv and Fenton pretreatments. The hemicellulose and cellulose in corncob were effectively degraded into xylose, glucose, and soluble glucose oligomers in a few hours. This saccharide solution, separated from the solid lignin simply by filtration, can be directly applied to the subsequent enzymatic hydrolysis and ethanol fermentation.

RESULTS

After the pretreatment, 94% carbohydrates were recovered as soluble monosaccharide (xylose and glucose) and glucose oligomers in the filtrates, and 87% of solid lignin was recovered as the filter residue. The filtrates were directly applied to enzymatic hydrolysis, and 92% of raw corncob glucose was recovered. The hydrolysates containing the glucose and xylose from the enzymatic hydrolysis were directly applied to ethanol fermentation with ethanol yield equals 79% of theoretical yield. The pretreatment conditions (130 °C, 1.5 bar; 30 min to 4 h) are mild, and the pretreatment reagents (H₂O₂, FeCl₃, and solvent) had low impact to environment. Using ferrimagnetic Fe₃O₄ resulted in similar pretreatment efficiency and Fe₃O₄ could be removed by filtration.

CONCLUSIONS

A modified Fenton pretreatment of corncob in DMSO/water was developed. Up to 94% of the carbohydrate content of corncob was recovered as a saccharide solution simply by filtration. Such filtrate was directly applied to the subsequent enzymatic hydrolysis and where 92% of the corncob glucose content was obtained. The hydrolysate so obtained was directly applied to ethanol fermentation with good fermentability. The pretreatment method is simple, and the additives and solvents used have a low impact to the environment. This method provides the opportunity to substantially maximize the carbohydrate and solid lignin recovery of biomass with a comparatively green process, such that the efficiency of biorefinery as well as the bioethanol production process can be improved. The pretreatment is still relatively energy intensive and expensive, and further optimization of the process is required in large-scale operation.

Green and chemical-free process of enzymatic xylooligosaccharide production from corncob: Enhancement of the yields using a strategy of lignocellulosic destructuration by ultra-high pressure pretreatment

In this study, the pressures at 50-500MPa were evaluated at different time to pretreat and further enzyme hydrolysis. The ultra-high pressure (UHP) pretreatment at 100MPa for 10min led to improved accessibility of enzyme for conversion of xylan to xylooligosaccharide (XOS). The maximum XOS yield of 35.6mg/g substrate was achieved and firstly reported at 10% (w/v) of substrate, 100U of endo-xylanase/g corncobs and incubation time of 18h. The enzymatic hydrolysis efficiency was increased by 180.3% and released a high amount of xylobiose. The UHP pretreatment relatively did not affect to the composition of corncob, but decreased 34.3% of lignin. Interestingly, antioxidant activities of XOS using UHP pretreatment were higher than untreated corncob. The UHP pretreatment improved lignocellulosic destructuration and XOS yields in a shorter time without the need of chemicals, implying that UHP could be an effective pretreatment of biomass with a chemical-free process.

Phytochemicals in Capsicum oleoresin from different varieties of hot chilli peppers with their antidiabetic and antioxidant activities due to some phenolic compounds

Due to its wide use in nutritional therapy, a capsicum oleoresin extraction from hot chilli pepper was optimized using ultrasound assisted extraction. Under optimal conditions, a 0.1g sample in 10mL of a 20% water in methanol solution was extracted at 50°C for 20min to remove phytochemicals consisting of oleoresin, phenolics, carotenoids, flavonoids, capsaicinoids (pungency level), reducing sugars. Antioxidant and antidiabetic activities of the crude extracts from 14 chilli pepper varieties were examined. The antioxidant and antidiabetic activities of some phenolic compounds were also tested individually. The results showed that these chilli pepper samples are a rich source of phytochemicals with antioxidant and antidiabetic activities. High antioxidant activity of the extracts was evaluated using the 2,2-diphenyl-1-picrylhydrazyl, N,N-dimethyl-p-phenylenediamine dihydrochloride, 2,2'-azino-bis(3-ethylbenzothiazolin-6-sulfonic acid) and ferric ion reducing antioxidant power assays. The crude extracts had a lower level of sugars induced by the inhibitory effect of α-amylase activity. Thus, their enzymatic inhibitory effect might have resulted from a synergism among the phytochemicals concerned. Therefore, a diet with this type of food may have beneficial health effects.

Comparison of ultrasound-assisted Fenton reaction and dilute acid-catalysed steam explosion pretreatment of corncobs: cellulose characteristics and enzymatic saccharification

As an emerging method for lignocellulose pretreatment, the ultrasound-assisted Fenton reaction is not well developed in comparison to the dilute acid-catalysed steam explosion.