Quantitative characterization of enzyme adsorption and hydrolytic performance for ultrafine grinding pretreated corn stover

Microbial composition play the leading role in volatile fatty acid production in the fermentation of different scale of corn stover with rumen fluid

Rumen fluid is a natural and green biocatalyst that can efficiently degrade biomass into volatile fatty acid (VFA) used to produce value-added materials. But the essence of high degradation efficiency in the rumen has not been fully analyzed. This study investigated the contribution of substrate structure and microbial composition to volatile fatty acid production in the fermentation of corn stover. The ball milled corn stover were innovatively applied to ferment with the rumen fluid collected at different digestion times. Exogeneous cellulase was also added to the ruminal fermentation to further reveal the inner mechanism. With prolonged digestion time, the microbial community relative abundance levels of Bacteroidetes and Firmicutes increased from 29.98% to 72.74% and decreased from 51.76% to 22.11%, respectively. The highest VFA production of the corn stover was achieved via treatment with the rumen fluid collected at 24 h which was up to 9508 mg/L. The ball milled corn stover achieved high VFA production because of the more accessible substrate structure. The application of exogenous cellulase has no significant influence to the ruminal fermentation. The microbial community abundance contributed more to the VFA production compared with the substrate structures.

Qualitative and Quantitative Correlation of Microstructural Properties and In Vitro Glucose Adsorption and Diffusion Behaviors of Pea Insoluble Dietary Fiber Induced by Ultrafine Grinding

Ultrafine grinding is an important pretreatment to achieve the physical modification of dietary fiber. In this study, ultrafine grinding treatments were performed for different times to give pea insoluble dietary fiber (PIDF) samples with varied particle sizes (D50). The correlations and quantitative relationships between the microstructures of multi-scales PIDF and its in vitro glucose adsorption and diffusion behaviors were comprehensively evaluated. The results indicated that the specific surface area (SSA), pore volume (PV) and oxygen-to-carbon surface ratio (O/C) of PIDF were significantly increased by ultrafine grinding at the cellular scale, while D50 and cellulose crystallinity (CrI) were significantly decreased. These changes significantly improved the glucose adsorption capacity (GAC) of PIDF. The order of importance of microstructural changes on GAC was O/C > PV > SSA > CrI > D50. GAC showed positive exponential relationships with SSA, PV, and O/C and showed a negative linear relationship with CrI. The ability to retard glucose diffusion increased significantly with decreased fiber particle size because of improved adsorption and interception of glucose and the dense physical barrier effect of PIDF. The quantitative equation of maximum glucose dialysis retardation index was GDRImax = −1.65 ln(D50) + 16.82 ln(GAC) − 68.22 (R2 = 0.99). The results could provide theoretical support for quantitative and targeted intervention of dietary fiber structure for blood glucose control.

Effect of combined wet alkaline mechanical pretreatment on enzymatic hydrolysis of corn stover and its mechanism

BACKGROUND

To further optimize the mechanochemical pretreatment process, a combined wet alkaline mechanical pretreatment of corn stover was proposed with a short time and less chemical consumption at room temperature.

RESULTS

The combined alkaline mechanical pretreatment significantly enhanced enzymatic hydrolysis resulting a highest glucose yield (Y_G) of 91.9% with 3% NaOH and ball milling (BM) for 10 min. At this optimal condition, 44.4% lignin was removed and major portion of cellulose was retained (86.6%). The prehydrolysate contained by-products such as monosaccharides, oligosaccharides, acetic acid, and lignin but no furfural and 5-HMF. The alkaline concentration showed a significant impact on glucose yield, while the BM time was less important. Quantitative correlation analysis showed that Y_G (%) = 0.68 × BM time (min) + 19.27 × NaOH concentration (%) + 13.71 (R² = 0.85), Y_G = 6.35 × glucan content - 231.84 (R² = 0.84), and Y_G =  - 14.22 × lignin content + 282.70 (R² = 0.87).

CONCLUSION

The combined wet alkaline mechanical pretreatment at room temperature had a boosting effect on the yield of enzymatic hydrolysis with short treatment time and less chemical consumption. The impact of the physical and chemical properties of corn stover pretreated with different BM times and/or different NaOH concentrations on the subsequent enzymatic hydrolysis was investigated, which would be beneficial to illustrate the effective mechanism of the mechanochemical pretreatment method.

Solvent-free mechanochemical preparation of graphene oxide-Fe3 O4 and its application in magnetic dispersive solid-phase extraction of illegal dyes in food samples

A simple, green, and efficient mechanochemical approach was developed herein to prepare tunable magnetic graphene oxide nanoparticles. The obtained nanoparticles were successfully used as adsorbents in a magnetic dispersive solid-phase extraction method to extract three cationic dyes (i.e., thioflavine T, auramine-O, and basic orange 2) found in food samples. Our proposed approach also utilized high-performance liquid chromatography with ultraviolet detection. Several key variables affecting the extraction recovery were investigated. These included the sample pH, amount of extractant, extraction time, sample volume, elution solvent type and volume, and the stability and reusability of the magnetic graphene oxide nanoparticles. Under optimized conditions, the calibration curve was linear at a concentration range of 0.005-1.0 μg/mL with a correlation coefficient of 0.9992-0.9996. Moreover, the limits of detection were determined at 0.97-1.35 μg/mL. The extraction mechanism was investigated via ultraviolet-visible spectrophotometry and zeta-potential analyses. The developed method was used to analyze the above-mentioned cationic dyes in bean products and yellow fish samples. Notably, satisfactory spiked recoveries ranging from 90.7 to 104.9% were achieved.

Enhanced adsorption of Congo red using chitin suspension after sonoenzymolysis

In the present work, chitin suspensions after enzymolysis and sonoenzymolysis were taken as adsorbents to evaluate the adsorption properties of Congo red (CR) dyes. Compared with untreated chitin suspension, the CR adsorption performance was significantly improved after enzymolysis and even more after sonoenzymolysis. According to different adsorption kinetic and isotherm models, Langmuir isotherm and the pseudo-second order model were more reliable to describe the adsorption process of CR onto different chitin samples and demonstrated a monolayer and favorable physisorption process. What's more, negative values of ΔG (Gibbs free energy change) and the shifts to higher negative values with the temperature increasing from adsorption thermodynamic study proved a spontaneous CR adsorption process. The structural characterization before and after adsorption further verified the physical adsorption between chitin and CR, and a larger specific area and higher porosity of chitin suspension was obtained after sonoenzymolysis with more available active sites.

Insight on adsorption of cellulase on wet ground corncob residues and its evaluation by multivariate linear analysis

Understanding the adsorption behavior and the interaction between substrates and enzymes are critical to improving enzymatic hydrolysis efficiency and reducing bioconversion cost. Herein, the adsorption of cellulase on wet ground corncob residues was studied, and the effects of main characteristics of wet ground corncob residues on adsorption capacity were quantitatively analyzed with the combination of principal component analysis and multiple linear regression models. The results showed that the adsorption of cellulase on wet ground corncob residues was fitted well with Langmuir isotherm adsorption and pseudo second-order kinetics model, the adsorption rate and adsorption capacity were greatly enhanced with increasing grinding time; the multiple linear regression models describing the relationship between main characteristics of corncob residues and adsorption capacity to cellulase were established; the significance of these characteristics were in the following order: average particle size, crystallinity index, specific surface area, surface lignin concentration, water retention value, and surface charge density.

Solvent-free synthesis of magnetic biochar and activated carbon through ball-mill extrusion with Fe3O4 nanoparticles for enhancing adsorption of methylene blue

Magnetic carbonaceous adsorbents were synthesized by ball-milling biochar (BC) or activated carbon (AC) with Fe₃O₄ nanoparticles, and their capacities to sorb methylene blue (MB) from water were evaluated and compared. Ball milling with magnetite not only improved the surface properties of the carbonaceous adsorbents, especially BC, but also introduced magnetic properties through mechanical extrusion. Furthermore, ball-mill extrusion increased the MB adsorption capacity of BC at all pH values by 14-fold, on average, but BC ball milled with magnetite had even greater MB adsorption capacity (27-fold, greater, on average). While ball milling of AC also improved its MB adsorption capacity (by almost 3-fold, on average), ball milling with magnetite did not further improve its MB adsorption capacity. All the magnetic adsorbents showed fast MB adsorption kinetics, reaching equilibrium within about 8 h. The Langmuir maximum MB adsorption capacity of the magnetic ball-milled BC (MBM-BC) was the highest (500.5 mg/g) among all the samples including the ones derived from AC. After five adsorption-desorption cycles, MBM-BC maintained about 80% MB removal capacity. The high MB adsorption capacity of MBM-BC was attributed to its increased surface area, opened pore structure, functional groups and aromatic CC bonds, which promoted π-π and electrostatic interactions. Findings from this study indicate that the magnetic ball-milled BC is a promising adsorbent due to its environmentally friendly synthesis, high efficiency, low cost, and convenience in operation.

Comparison and intrinsic correlation analysis based on composition, microstructure and enzymatic hydrolysis of corn stover after different types of pretreatments

Pretreatment is a key step in the energy utilization of lignocellulosic biomass. Different types of pretreatments (ultrafine grinding pretreatment, alkaline hydroxide peroxide pretreatment, dilute acid pretreatment, and ammonia fiber expansion pretreatment) were conducted on corn stover. The lignocellulosic composition, microstructural parameters, and glucose yield of differently pretreated corn stover were characterized and compared. Then qualitative and quantitative correlation analyses of the parameters were carried out to explore the correlations among the composition, microstructure properties, and enzymatic hydrolysis efficacy of corn stover after different types of pretreatments and identify the main properties affecting enzymatic hydrolysis. Qualitative correlation analysis found that cellulose content, specific surface area, pore volume, enzyme-accessible pore volume, and surface area of cellulose had significant positive correlations with glucose yield. The results of quantitative correlation analysis were GY = 15.01 × cellulose content-339.05, GY = 13.06 × SSA + 172.35, GY = 7226.27 × PV + 129.14, GY = 8628.61 × EAPV + 125.61, and GY = 1.18 × SAC-287.21.

Mechanochemical deconstruction of lignocellulosic cell wall polymers with ball-milling

In this work, the deconstruction mechanism of corn stover cell wall polymers during ball milling was evaluated. The characterization showed that ball milling not only brought about the dissociation of the cross-linked cellulose-hemicellulose-lignin complex but also led to the depolymerization of the cell-wall polymers especially the carbohydrates. Micromorphology characterization revealed that mechanical treatment disrupted the orderly fibrillar matrices with a porous structure. The breakage of β-1,4 glycosidic bonds in cellulose and the decomposition of arabinoxylans indicated the modification in polysaccharide chains. The degradation of lignin-carbohydrate complex (LCC) linkages and the cleavage of β-O-4' linkages in lignin approved the partial degradation of lignin. In conclusion, mechanochemistry is an efficient force to make the polymers in plant fibers more digestible.

A comparative study on enzyme adsorption and hydrolytic performance of different scale corn stover by two-step kinetics

To investigate the effect of two-step kinetics on enzyme adsorption and hydrolytic properties of different structural substrates at low enzyme doses. The two-step kinetic experiments of ultrafine grinding (UGCS) and sieve-based grinding corn stover (SGCS) were performed respectively with enzyme loading of 2.5 + 2.5 FPU/g and 5 + 5 FPU/g. The different performance of these two samples were illustrated by characterizing the particle size distribution, SEM and XPS. The results showed that ultrafine grinding can promote the structural properties which is beneficial to adsorption and hydrolysis. The main factors influencing adsorption kinetics are enzyme concentration and the surface cellulose amount. Pre-adsorbed enzyme has no effects on the subsequent enzyme adsorption quantity but produces some small competitive and impeditive effects. The hydrolysis kinetics mainly depend on the structure of the substrate and its complexity of hydrolysis. The two-step hydrolysis didn't promote the total sugar yield under the same enzyme concentration, but the first step contributed more to the total sugar yield.

Daptomycin adsorption on magnetic ultra-fine wood-based biochars from water: Kinetics, isotherms, and mechanism studies

The adsorption of a new antibiotic, daptomycin, on two magnetic ultra-fine wood-based biochars were investigated in detail using batch experiments. The adsorbent materials was prepared by ball milling method, which was characterized by laser particle size analyzer, elemental analyzer, ICP-OES, VSM, BET, TG-DTG, FTIR and SEM. Furthermore, the effects of most important variables in the adsorption process, including solution pH, contact time, initial concentration and temperatures were investigated. The results exhibited that the adsorption of daptomycin was highly pH-dependent, and the capacity decreased with increasing pH. The adsorption process follows pseudo-first order and pseudo-second order models, analysis indicated that their adsorption was dominantly by physisorption. Equilibrium data were fitted well with Freundlich isotherm model, implying a multilayer adsorption. Thermodynamic parameters demonstrated that the adsorption was spontaneous, endothermic and increased randomness process. Mechanism study suggested the boundary layer diffusion was the rate limiting step.

Understanding the synergistic effect and the main factors influencing the enzymatic hydrolyzability of corn stover at low enzyme loading by hydrothermal and/or ultrafine grinding pretreatment

A thorough assessment of the microstructural changes and synergistic effects of hydrothermal and/or ultrafine grinding pretreatment on the subsequent enzymatic hydrolysis of corn stover was performed in this study. The mechanism of pretreatment was elucidated by characterizing the particle size, specific surface area (SSA), pore volume (PV), average pore size, cellulose crystallinity (CrI) and surface morphology of the pretreated samples. In addition, the underlying relationships between the structural parameters and final glucose yields were elucidated, and the relative significance of the factors influencing enzymatic hydrolyzability were assessed by principal component analysis (PCA). Hydrothermal pretreatment at a lower temperature (170 °C) combined with ultrafine grinding achieved a high glucose yield (80.36%) at a low enzyme loading (5 filter paper unit (FPU)/g substrate) which is favorable. The relative significance of structural parameters in enzymatic hydrolyzability was SSA > PV > average pore size > CrI/cellulose > particle size. PV and SSA exhibited logarithmic correlations with the final enzymatic hydrolysis yield.

A carbonised sieve-like corn straw cellulose–graphene oxide composite for organophosphorus pesticide removal

The development of efficient adsorbents for the removal of organophosphorus pesticides from water is a major challenge. In this work, we prepared an activated carbon derived from sieve-like cellulose/graphene oxide composites (ACCE/G) for the removal of several organophosphorus pesticides. We employed corn straw to produce a sieve-like cellulose–graphene oxide composite (CCE/G); then, by treating CCE/G with potassium hydroxide at high temperatures, the efficient adsorbent ACCE/G was prepared. The adsorption capacity of ACCE/G is higher than those of other sorbents, including a multi-wall carbon nanotube, graphitised carbon black, activated carbon, C18, and primary secondary amine adsorbent. The ACCE/G structure has been fully characterised via scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and Brunauer–Emmett–Teller analysis. The maximum adsorption capacity of ACCE/G is 152.5 mg g⁻¹ for chlorpyrifos. The mechanism, the thermodynamic properties, and the kinetics of the adsorption process have been investigated as well. Our findings demonstrate that the adsorption mechanism depends on the electron-donating abilities of the S and P atoms. Moreover, the Langmuir model gives the best fit for the isotherm data, and the adsorption efficiency of the ACCE/G is still over 80% after eight times of recycling, making ACCE/G a valuable candidate for the removal of OPPs.

Synthesizing a reusable adsorbent from waste corn straw is a sustainable way to utilize secondary resources and purify water.