Analytical Characterization and Inhibitor Detection in Liquid Phases Obtained After Steam Refining of Corn Stover and Maize Silage

The utilization of agricultural products and residues for the production of value-added and biobased products is a highly relevant topic in present research. Due to the natural recalcitrance of lignocellulosic biomass against enzymatic degradation, pretreatments are important requirement for further processes. For the raw material in this study, corn stover (CS) as highly available agricultural residue and maize silage (MS) as model substrate for an ensiled agricultural product were pretreated by steam refining. However, after processing a liquid fraction and fibers are present. Subsequent to steaming the fiber fraction is well characterized. Nonetheless, in depth characterizations of the filtrates are also important for their subsequent utilization. Decreasing molar masses from 7,900 g/mol to 1,100 g/mol for CS filtrates and 100.000–12.900 g/mol for MS filtrates were determined with increasing severity. Due to their proven inhibitory effect on microorganisms weak acids, furans and phenolic compounds within the liquid phased were analyzed. Especially formic acid increases with increasing severity from 0.27 to 1.20% based on raw material for CS and from 0.07 to 0.23% based on raw material for MS. Further GC/MS measurements indicate, that up to 8.25% (CS filtrate) and 5.23% (MS filtrates) of the total peak area is related to inhibitory phenols. Considering the data, detoxification strategies are of non-negligible importance for filtrates after steam refining and should be considered for further research and process or parameter optimizations. An alternative may be the application of milder process conditions in order to prevent the formation of inhibitory degradation products or the dilution of the gained filtrates.

Recycling of Waste MDF by Steam Refining: Evaluation of Fiber and Paper Strength Properties

Currently, most of the collected waste medium-density fiberboards (MDF) is incinerated or landfilled, as economically viable recycling methods are yet to be developed. By steam refining waste medium-density fiberboards (MDF), it is possible to hydrolyze the incorporated resins and isolate a high yield fiber fraction. Further refining of the steam treated fibers might enable the fibers to be utilized in applications such as paper packaging, facilitating a cascading use of the waste material stream. To this end, intimate knowledge of the material is needed. In this study, the steam refined fibers of two waste MDF samples containing differing amounts of softwood and hardwood underwent refining and beating. The resulting fibers were characterized regarding their morphology and paper test sheets were produced to evaluate their strength (compression-, tensile- and tear-strength). Distinct differences in response to refining between the MDF samples were apparent. For the sample with the higher hardwood share an increase in strength properties with increasing steam treatment severities could be observed and it was possible to produce test sheets with comparable compression strength to recycled pulp for industrial corrugated paperboard. For the sample with a higher share of softwood, the steam treatment severity did not show any influence on fiber morphology or paper properties, and the resulting paper strength was low in comparison to the other steam refined waste MDF sample. Graphic Abstract

Chemical Properties and Therapeutic Potential of Citral, a Monoterpene Isolated from Lemongrass

Background: Citral is one of the main components of lemongrass oil present at a concentration of 65-85% approximately and is generally separated by steam refining. It is an important component in the manufacturing of scents, citrus chemicals, cosmetics, food and pharmaceutical products. Objectives: This article aims at reviewing the published literature to highlight the metabolism, extraction strategies and therapeutic significance of citral for improving the scope of its application in the food and pharma industry. Discussions: Apart from steam refining, there are other techniques like solvent extraction, supercritical fluid extraction and ultrasonication by which citral can be extracted and the method of extraction defines its quality. It is an unstable molecule and undergoes rapid deterioration on exposure to air. Citral is biosynthesized by the plants through the 5 carbon precursor isopentenyl diphosphate (IPP) units utilizing two diverse biochemical pathways, acetate– mevalonate (acetate– MVA) pathway or 2C-methylerythritol-4-phosphate (MEP). Orally Citral was absolutely digested in the gastrointestinal tract and its metabolism leads to the discharge of metabolites which include a number of acids and a biliary glucuronide. There is no scientific evidence about the long term bioavailability of citral in the body and it has no adverse effect on tissue related to its accumulation and delayed excretion. Citral exhibits various important therapeutic properties like antimicrobial, antioxidant, anticancer, anti-diabetic and anti-inflammatory. Conclusions: Citral is a potent biomolecule with various important biological activities and therapeutic implications. Strategies are required to increase the stability of citral which could increase its applications.

Maize Silage Pretreatment via Steam Refining and Subsequent Enzymatic Hydrolysis for the Production of Fermentable Carbohydrates

Maize, also called corn, is one of the most available feedstocks worldwide for lignocellulosic biorefineries. However, a permanent biomass supply over the year is essential for industrial biorefinery application. In that context, ensiling is a well-known agricultural application to produce durable animal feed for the whole year. In this study, ensiled maize was used for steam refining experiments with subsequent enzymatic hydrolysis using the Cellic® CTec2 to test the application possibilities of an ensiled material for the biorefinery purpose of fermentable carbohydrate production. Steam refining was conducted from mild (log R0 = 1.59) to severe conditions (log R0 = 4.12). The yields were determined, and the resulting fractions were characterized. Hereafter, enzymatic hydrolysis of the solid fiber fraction was conducted, and the carbohydrate recovery was calculated. A conversion to monomers of around 50% was found for the mildest pretreatment (log R0 = 1.59). After pretreatment at the highest severity of 4.12, it was possible to achieve a conversion of 100% of the theoretical available carbohydrates. From these results, it is clear that a sufficient pretreatment is necessary to achieve sufficient recovery rates. Thus, it can be concluded that ensiled maize pretreated by steam refining is a suitable and highly available feedstock for lignocellulosic biorefineries. Ultimately, it can be assumed that ensiling is a promising storage method to pave the way for a full-year biomass supply for lignocellulosic biorefinery concepts.

A TOTAL SURVEY ON LEAVES OF MELALEUCA ALTERNIFOLIA (TEA TREE OIL)

Tea tree oil, a basic oil extricated from the leaves of Melaleuca alternifolia by steam refining, supercritical liquid extraction, soxhlet extraction followed by progressive extraction and small scale stove extraction forms by various solvents has discovered a wide scope of antimicrobial exercises as antiviral, antifungal, antibacterial, against protozoval because of the nearness of terpinen–4-ol as the significant constituent. TTO was contain flavonoids, glycosides, quinolines, starches and so forth. TTO is considered and the rate yield of tea tree oil extricated is resolved and the piece of tea tree absolutes (terpinen-4-ol, 1,8-cineole, γ-terpinene and α-terpineol) separated was contrasted and standard tea tree oil just as with ISO 4730 TTO has discovered the mitigating and hostile to skin break out vulgaris, Psoriasis, free radical rummaging exercises. Tea tree oil is normal items, so it is non-harmful, effectively available, biodegradable, and biocompatible. The few points of interest of tea tree oil make it one of the gainful item having helpful impacts. The current audit article depends on the use of tea tree oil, extraction procedure of tea tree oil, constituents, security contemplations and so on.

Steam Refining with Subsequent Alkaline Lignin Extraction as an Alternative Pretreatment Method to Enhance the Enzymatic Digestibility of Corn Stover

Agricultural residues are promising and abundant feedstocks for the production of monomeric carbohydrates, which can be gained after pretreatment and enzymatic hydrolysis. These monomeric carbohydrates can be fermented to platform chemicals, like ethanol or succinic acid. Due to its high availability, corn stover is a feedstock of special interest in such considerations. The natural recalcitrance of lignocellulosic material against degradation necessitates a pretreatment before the enzymatic hydrolysis. In the present study, a novel combination of steam refining and alkaline lignin extraction was tested as a pretreatment process for corn stover. This combination combines the enhancement of the enzymatic hydrolysis and steam refining lignin can be gained for further utilization. Afterward, the obtained yields after enzymatic hydrolysis were compared with those after steam refining without alkaline extraction. After steam refining at temperatures between 160 °C and 210 °C and subsequent enzymatic hydrolysis with Cellic® CTec2, it was possible to enhance the digestibility of corn stover and to achieve 65.4% of the available carbohydrates at the lowest up to 89% at the highest conditions as monomers after enzymatic hydrolysis. Furthermore, the enzymatic degradation could be optimized with a subsequent alkaline lignin extraction, especially at low severities under three. After this combined pretreatment, it was possible to enhance the enzymatic digestibility and to achieve up to 106.4% of the available carbohydrates at the lowest conditions and up to 102.2% at the highest temperature as monomers after following enzymatic hydrolysis, compared to analytical acid hydrolysis. Regarding the utilization of the arising lignin after extraction, the lignin was characterized with regard to the molar mass and carbohydrate impurities. In this context, it was found that higher amounts and higher purities of lignin can be attained after pretreatment at severities higher than four.

Fractionation of Waste MDF by Steam Refining

In view of the expected increase in available waste medium-density fiberboard (MDF) and the current insufficient and unsatisfactory disposal capacities, efficient ways of recycling the waste material need to be developed. In this study, the potential of steam refining as a method to hydrolyze the resins, isolate fibers, and obtain a hemicellulose-rich extract available for further utilization in the context of a biorefinery was assessed. Two different MDF waste samples, as well as poplar (Populus spp.) and spruce (Picea spp.) wood chips for benchmarking, were treated over a severity range from 2.47 to 3.95. The separated fiber and extract fractions were analyzed with regard to yield, content of carbohydrates, acids, degradation products, and nitrogen. A fiber fraction of more than 70% yield and an extract containing up to 30% of carbohydrates for further processing can be gained by steam-refining waste MDF. At low severities, most of the nitrogen-based compounds are solubilized. Increasing the severity leads to a decrease in nitrogen in the extract as the nitrogen compounds are converted into volatiles. A non-hydrolysable resin residue remains on the fibers, independent of the treatment severity. In comparison to the benchmark samples, the extract fraction of waste MDF shows a high pH of 8 and high amounts of acetic and formic acid. The generation of furfural and 5-hydroxymethylfurfural (5-HMF) on the other hand is suppressed. Distinct differences in carbohydrate hydrolysis behavior between waste MDF and conventional wood can be observed. Especially, the mannose-containing constituents seem to be resistant to hydrolysis reactions in the milieu created in MDF fractionation.

Steam pretreatment for enzymatic hydrolysis of poplar wood: comparison of optimal conditions with and without SO2 impregnation

Steam refining of non-debarked poplar wood with SO2 impregnation prior to steaming was investigated as pretreatment for enzymatic hydrolysis. Pretreatment conditions were varied in the range of 170°C–220°C, 3–30 min and 0.7–2.5% SO2 according to a factorial design. Predicted steaming conditions for highest carbohydrate yields after enzymatic hydrolysis were at 200°C, 15 min, and 2.5% SO2. The yield of glucose and xylose from control tests under these conditions was 43% representing an increase of 9% compared to results of former experiments without SO2 impregnation. Investigations on lignin extracted from the fibers revealed no distinct differences between pretreatment with and without SO2. No sulfonation occurred by the impregnation with SO2. Topochemical analyses of the fibers by cellular UV microspectrophotometry (UMSP) showed an inhomogeneous lignin distribution within the S2 of fibers after pretreatment without SO2 and local depositions of high UV-absorbing substances in the lumina of fibers and parenchyma cells. The lignin distribution of fiber cell walls after pretreatment with SO2 was more homogeneous with a preserved fiber network and only little amounts of deposited phenolic compounds in the lumina. Therefore, it might be concluded that the expulsion of lignin hinders the enzymes in accessing the cellulose.

Optimization of steam pretreatment conditions for enzymatic hydrolysis of poplar wood

Steam refining was investigated as a pretreatment for enzymatic hydrolysis of poplar wood from a short rotation plantation. The experiments were carried out without debarking to use an economically realistic raw material. Steam refining conditions were varied in the range of 3–30 min and 170–220°C, according to a factorial design created with the software JMP from SAS Institute Inc., Cary, NC, USA. Predicted steaming conditions for highest glucose and xylose yields after enzymatic hydrolysis were at 210°C and 15 min. Control tests under the optimized conditions verified the predicted results. Further pretreatments without bark showed that the enzymes were not significantly inhibited by the bark. The yield of glucose and xylose was 61.9% of theoretical for the experiments with the whole raw material, whereas the yield for the experiments without bark was 63.6%. Alkaline extraction of lignin from the fibers before enzymatic hydrolysis resulted in an increase of glucose yields from mild pretreated fibers and a decrease for severe pretreated fibers. The extracted lignin had a high content of xylose of up to 14% after very mild pretreatments. On the other hand, molecular weights of the extracted lignin increased substantially after pretreatments with a severity factor above 4. Hence, alkaline extraction of the lignin seems only attractive in a narrow range of steaming conditions.