Steam Explosion Pretreatment Research Articles

Preliminary study on integrated production of ethanol and lignin from bagasse pulp waste

Bagasse pulp waste (BPW) is a material generated from the depithing of sugarcane bagasse stems prior to pulping. It was subjected to a modified oxygen delignification or ammonia catalytic steam explosion (AE) pretreatment for delignification and retaining carbohydrates of raw materials, followed by simultaneous saccharification and co-fermentation (SSCF) to ethanol. Based on this process, an environmentally sustainable two-stage process for lignin purification was employed to obtain nontoxic “green lignin”. The results indicated that both pretreatment methods, particularly AE, had outstanding performance in the SSCF process. The highest ethanol yield (based on dry matter of BPW), 67.5% for the AE pretreatment, was obtained from the SSCF procedure at 8% (w/v) solids loading. Furthermore, the obtained lignin products from this process possessed better structural integrity.

Xylooligosaccharides from steam-exploded barley straw: Structural features and assessment of bifidogenic properties

The biorefinery concept integrates the production of energy and bioproducts from biomass. In this philosophy, barley straw samples were used as raw material for the production of xylooligosaccharides (XOS) mixtures from soluble hemicelluloses by steam-explosion pretreatment. This fraction was treated by ion-exchange (XOS1) and a combination of membrane filtration, enzymatic hydrolysis, and ion-exchange processes (XOS2) to produce prebiotic compounds. The afforded products were then characterized by using analytical techniques, including HPAEC-PAD, FTIR, and MALDI-TOF-MS. XOS2 is composed of a backbone of xylopyranosyl branched, which including acetyl-esterified oligosaccharides and feruloyl substituted arabino-oligosaccharides.Further, the prebiotic potential was evaluated by in vitro fermentation experiments using as inocula human fecal samples from volunteers in which the short-chain fatty acids production, total bacteria growth, and the bifidobacteria numbers were quantified and compared to the results obtained with commercial fructooligosaccharides.The accumulation of short-chain fatty acids was similar for XOS1 and XOS2 (102.7 and 117.2 mM). An increase of 1.50 and 1.43 log cell number/mL-fold was observed for media containing XOS1 and XOS2, respectively. Results obtained confirm that the production and use of XOS derived from steam-exploded barley straw such as functional ingredient is an alternative for the valorization of its hemicelluloses fraction into the “biorefinery” context.

Saccharification Yield through Enzymatic Hydrolysis of the Steam-Exploded Pinewood

Pressure, temperature, and retention time are the most studied parameters in steam explosion pretreatment. However, this work aimed to fix these parameters and to evaluate the influences of several less investigated steam explosion parameters on the saccharification yield in hydrolysis. In this study, firstly, pinewood samples smaller than 200 µm were treated with steam explosion at 190 °C for 10 min. The variable parameters were biomass loading, N2 pressure, and release time. Steam-exploded samples were hydrolyzed with the Trichoderma reesei enzyme for saccharification for 72 h. The sugar content of the resultant products was analyzed to estimate the yield of sugars (such as glucose, xylose, galactose, mannose, and arabinose). The best glucose yield in the pulp was achieved with 4 g of sample, N2 pressure of 0.44 MPa, and short release time (22 s). These conditions gave a glucose yield of 97.72% in the pulp, and the xylose, mannose, galactose, and arabinose yields in the liquid fraction were found to be 85.59%, 87.76%, 86.43%, and 90.3%, respectively.

Steam Explosion Pretreatment Changes Ruminal Fermentation in vitro of Corn Stover by Shifting Archaeal and Bacterial Community Structure.

Steam explosion is an environment-friendly pretreatment method to improve the subsequent hydrolysis process of lignocellulosic biomass. Steam explosion pretreatment improved ruminal fermentation and changed fermentation pattern of corn stover during ruminal fermentation in vitro. The study gave a comprehensive insight into how stream explosion pretreatment shifted archaeal and bacterial community structure to change ruminal fermentation in vitro of corn stover. Results showed that steam explosion pretreatment dramatically improved the apparent disappearance of dry matter (DM), neutral detergent fiber (NDF), and acid detergent fiber (ADF). Steam explosion pretreatment significantly increased the molar proportion of propionate and decreased the ratio of acetate to propionate. At archaeal level, steam explosion pretreatment significantly increased the relative abundance of Methanobrevibacter, which can effectively remove metabolic hydrogen to keep the fermentation continuing. At bacterial level, the shift in fermentation was achieved by increasing the relative abundance of cellulolytic bacteria and propionate-related bacteria, including Spirochaetes, Elusimicrobia, Fibrobacteres, Prevotella, Treponema, Ruminococcus, and Fibrobacter.

Sugars Production from Municipal Forestry and Greening Wastes Pretreated by an Integrated Steam Explosion-Based Process

Increasing awareness of resource sustainability and waste management has led to the search for solutions while promoting circular economy principles. Among all kinds of lignocellulosic biomass available, one with growing interest is municipal forestry and greening waste (MFGW). MFGW makes up an important part of waste streams of municipal solid waste and is a potential feedstock for biological conversion in a lignocellulosic biorefinery. This work studied the fermentable sugars production from MFGW after steam explosion (SE) pretreatment combined with other pretreatments such as dilute acid, organosolv, and metal salts. A range of pretreatment conditions was evaluated according to different parameters: sugars recovery, degradation product generation, and enzymatic hydrolysis yield. At selected pretreatment conditions (diluted acid plus SE, 195 °C, 10 min, and 60 mg H2SO4/g MFGW), 77% of potential sugars content in MFGW was obtained. The effect of solids loading and enzyme dose on glucose release and glucose yield on enzymatic hydrolysis were also determined. Up to 70% of the main sugars in the MFGW were recovered for the coupled pretreatment and enzymatic hydrolysis (45 FPU/g glucan enzyme loading and 20% dry matter solid consistency), resulting in 80 g/L glucose that could be further utilized for ethanol production.

Effect of wheat bran steam explosion pretreatment on flavors of nonenzymatic browning products

Wheat bran, which contains a large amount of cellulose, is used as a raw material to produce soy sauce, but it is hard to degrade during fermentation. Steam explosion (SE) is efficient in hydrolyzing the cellulose for enhancing enzymatic digestion and solvent accessibility. In this study, we applied a SE at a sufficiently high pressure to damage the integrity of the wheat bran structure and modify it to assume a layered form. We found that cellulose, hemicellulose, and lignin structures were collapsed by SE pretreatment, which was indicated by their changes in Fourier transform infrared spectroscopy (FTIR). The amounts of cellulose, hemicellulose, and lignin decreased by 5.8%, 21.4%, and 43.4%, respectively, under 1.5 MPa, resulting in the significant reduction of sugar and amino acid nitrogen. The co-reaction of nonenzymatic browning after SE pretreatment resulted in an intense increase in flavor (overall feeling), as determined by electronic nose analysis and sensory evaluation. In conclusion, SE pretreatment under 1.0 MPa was proven to be the most optimal state for the production of aroma compounds (volatile compounds), which are essential for soy sauce production.

Effect of Acid Production by Penicillium oxalicum on Physicochemical Properties of Bauxite Residue

Large-scale discharge of bauxite residue, an alkaline, saline and nutrient-deficient waste material produced in the process of alumina production, has created extreme environments that are challenging to restore. Microbial pathways have been found to play a critical role in the rehabilitation of these residues. In this study, Penicillium oxalicum, an alkali-resistant acid-producing fungus screened from bauxite residue disposal sites, was used to examine its effectiveness for restoration of bauxite residue. By comparing different biomass pretreatment methods, steam explosion pretreatment biomass was added to the medium to enhance microbial metabolism. Following the optimal biomass pretreatment, the contents of organic acids secreted by P. oxalicum were oxalic acid 0.12 mg/mL, formic acid 0.31 mg/mL and acetic acid 0.51 mg/mL, respectively. Addition of pretreatment biomass and microbes significantly lowered bauxite residue pH from 10.9 to 7.2, whilst increasing the electrical conductivity and enzyme activity. Furthermore, the metabolic process of this fungus may promote the release of basic ions dominated by Na+ and increase soluble cations. The results suggest that the combined application of biomass and microorganism could reduce the alkalinity of bauxite residue effectively, which may provide theoretical basis and practical reference for bioremediation in the disposal areas.

Nanofibrillation and characterization of sugarcane bagasse agro-waste using water-based steam explosion and high-pressure homogenization

Sugarcane bagasse waste, consisting of approximately 40–50% cellulose, has been widely used in a number of industries. The extraction and defibrillation of nanometer-scale cellulose fibers from such waste using strong chemical solutions have been extensively investigated. However, the using of strong chemical solutions can cause adverse effects to the fibers as well as negatively affect the environment. Some evidence has shown that mechanical treatments, such as steam explosion and high-pressure homogenization, are environmentally friendly when compared with chemical treatment techniques. This work aimed to isolate the cellulose nanofibers from sugarcane bagasse waste using steam explosion pretreatment at various temperatures (195, 200, 205, and 210 °C) and durations (5, 10, and 15 min) before passing through a microfluidizer within 12 passes of 200 mL cellulose suspension. The mean separation analysis using Duncan’s Multiple Range test showed that higher temperatures significantly improved the efficiency of non-cellulosic substances reduction, as evidenced by an increment of whiteness index (81.39–90.02), thermal degradation temperature (313.92–326.34 °C) and crystallinity index (74.27–81.42%). The obtained cellulose nanofibers exhibited very fine diameter within the range of 3–7 nm, had a high cellulose content (92.74 ± 0.14%) and a low density (0.8989 g/cm3). The obtained cellulose nanofibers could be applied in various fields such as medical, cosmetic, food packaging, and electronic device applications.

Steam Explosion Pretreatment of Beechwood. Part 1: Comparison of the Enzymatic Hydrolysis of Washed Solids and Whole Pretreatment Slurry at Different Solid Loadings

Steam explosion is a well-known process to pretreat lignocellulosic biomass in order to enhance sugar yields in enzymatic hydrolysis, but pretreatment conditions have to be optimized individually for each material. In this study, we investigated how the results of a pretreatment optimization procedure are influenced by the chosen reaction conditions in the enzymatic hydrolysis. Beechwood was pretreated by steam explosion and the resulting biomass was subjected to enzymatic hydrolysis at glucan loadings of 1% and 5% employing either washed solids or the whole pretreatment slurry. For enzymatic hydrolysis in both reaction modes at a glucan loading of 1%, the glucose yields markedly increased with increasing severity and with increasing pretreatment temperature at identical severities and maximal values were reached at a pretreatment temperature of 230 °C. However, the optimal severity was 5.0 for washed solids enzymatic hydrolysis, but only 4.75 for whole slurry enzymatic hydrolysis. When the glucan loading was increased to 5%, glucose yields hardly increased for pretreatment temperatures between 210 and 230 °C at a given severity, and a pretreatment temperature of 220 °C was sufficient under these conditions. Consequently, it is important to precisely choose the desired conditions of the enzymatic hydrolysis reaction, when aiming to optimize the pretreatment conditions for a certain biomass.

Steam Explosion Pretreatment of Beechwood. Part 2: Quantification of Cellulase Inhibitors and Their Effect on Avicel Hydrolysis

Biomass pretreatment is a mandatory step for the biochemical conversion of lignocellulose to chemicals. During pretreatment, soluble compounds are released into the prehydrolyzate that inhibit the enzymatic hydrolysis step. In this work, we investigated how the reaction conditions in steam explosion pretreatment of beechwood (severity: 3.0–5.25; temperature: 160–230 °C) influence the resulting amounts of different inhibitors. Furthermore, we quantified the extent of enzyme inhibition during enzymatic hydrolysis of Avicel in the presence of the prehydrolyzates. The amounts of phenolics, HMF, acetic acid and formic acid increased with increasing pretreatment severities and maximal quantities of 21.6, 8.3, 43.7 and 10.9 mg/gbeechwood, respectively, were measured at the highest severity. In contrast, the furfural concentration peaked at a temperature of 200 °C and a severity of 4.75. The presence of the prehydrolyzates in enzymatic hydrolysis of Avicel lowered the glucose yields by 5–26%. Mainly, the amount of phenolics and xylose and xylooligomers contributed to the reduced yield. As the maximal amounts of these two inhibitors can be found at different conditions, a wide range of pretreatment severities led to severely inhibiting prehydrolyzates. This study may provide guidelines when choosing optimal pretreatment conditions for whole slurry enzymatic hydrolysis.

Perspective pretreatment method of beech and poplar wood and wheat straw in 2G biofuel production processing

Monosaccharides such as glucose, xylose and arabinose are the main monomer units of which cellulose and hemicelluloses are composed. The cellulose and hemicelluloses content in many biomass species makes them suitable for 2G bioethanol production. Today, when 1G bioethanol production is closely monitored due to its enormous consumption of food raw materials such as wheat or corn grains, larger companies are gradually moving to pilot operations of 2G bioethanol production. However, cellulose and hemicelluloses contained in biomass are only very slightly accessible to enzymes used in 2G bioethanol production. Therefore pretreatment methods such as steam explosion are very suitable to use for fractionation of cell structure. In this paper, we tested the cellulose accessibility. We compared the cellulose accessibility of wheat straw particles with wooden particles obtained from beech and poplar. Particle size was less than 0.7 mm. We identified the optimal conditions of steam explosion pretreatment at reaction temperature of 200 °C for wheat straw, poplar and beech wood particles. The main indicator of accessibility was concentration of monomers obtained from enzymatic hydrolysis. The concentration of monomer was determined by high performance liquid chromatography. The experimental results showed different accessibility measure for each type of biomass species.

Development of optimal steam explosion pretreatment and highly effective cell factory for bioconversion of grain vinegar residue to butanol

BackgroundThe industrial vinegar residue (VR) from solid-state fermentation, mainly cereals and their bran, will be a potential feedstock for future biofuels because of their low cost and easy availability. However, utilization of VR for butanol production has not been as much optimized as other sources of lignocellulose, which mainly stem from two key elements: (i) high biomass recalcitrance to enzymatic sugar release; (ii) lacking of suitable industrial biobutanol production strain. Though steam explosion has been proved effective for bio-refinery, few studies report SE for VR pretreatment. Much of the relevant knowledge remains unknown. Meanwhile, recent efforts on rational metabolic engineering approaches to increase butanol production in Clostridium strain are quite limited. In this study, we assessed the impact of SE pretreatment, enzymatic hydrolysis kinetics, overall sugar recovery and applied atmospheric and room temperature plasma (ARTP) mutant method for the Clostridium strain development to solve the long-standing problem.ResultsSE pretreatment was first performed. At the optimal condition, 29.47% of glucan, 71.62% of xylan and 22.21% of arabinan were depolymerized and obtained in the water extraction. In the sequential enzymatic hydrolysis process, enzymatic hydrolysis rate was increased by 13-fold compared to the VR without pretreatment and 19.60 g glucose, 15.21 g xylose and 5.63 g arabinose can be obtained after the two-step treatment from 100 g VR. Porous properties analysis indicated that steam explosion can effectively generate holes with diameter within 10–20 nm. Statistical analysis proved that enzymatic hydrolysis rate of VR followed the Pseudop-second-order kinetics equation and the relationship between SE severity and enzymatic hydrolysis rate can be well revealed by Boltzmann model. Finally, a superior inhibitor-tolerant strain, Clostridium acetobutylicum Tust-001, was generated with ARTP treatment. The water extraction and enzymolysis liquid gathered were successfully fermented, resulting in butanol titer of 7.98 g/L and 12.59 g/L of ABE.ConclusionsSE proved to be quite effective for VR due to high fermentable sugar recovery and enzymatic hydrolysate fermentability. Inverse strategy employing ARTP and repetitive domestication for strain breeding is quite feasible, providing us with a new tool for solving the problem in the biofuel fields.

Enhanced separation of cellulose from bamboo with a combined process of steam explosion pretreatment and alkaline-oxidative cooking

Abstract A synergistic process with steam explosion pretreatment (SEP) followed by sodium carbonate-oxygen cooking (SCOC) upon bamboo was evaluated for its effect on separating hemicellulose and lignin from bamboo while preserving cellulose, providing cellulose substrate susceptible to chemicals in producing platform chemicals such as levulinic acid. The results showed that through the SEP with 2.5 MPa for 10 min, the hemicellulose content reduced by 60.85 %, the specific surface area of bamboo fiber increased to 1.9494 m2g-1 from 0.8061 m2g-1 of raw material. The synergistic SEP-SCOC significantly removed 73.33 % lignin, and yielded 73.9 % cellulose under the optimal condition of SEP with 2.5 MPa for 10 min and followed by SCOC with 30 % total titratable alkali (TTA) at 180 °C for 2 h and 2 MPa oxygen pressure. The results also proved the total lignin removal was improved by 8.07–18.95 % for the steam exploded bamboo fibers than the untreated one, indicating SEP increased the accessibility of cooking reagents to fibre during subsequent SCOC process. Furthermore, the low value of biological oxygen demand (BOD) and chemical oxygen demand (COD) in the final spent liquor indicated the lower pollution level of the process.

Tyrosinase inhibitory performance of hydrolysate from post-washing liquor of steam exploded corn stalk and its fractionation enhancement

In this work, corn stalk was subjected to steam explosion (SE) pretreatment, and the hydrolysate in post-washing liquor of steam exploded corn stalk was assayed for anti-tyrosinase activity for the first time. The hydrolysate showed strong anti-tyrosinase activity with an IC50 of 2.17 mg/mL (inhibitor concentration when 50% of tyrosinase activity is inhibited) at SE severity of 4.20 (198 °C, 20 min). Through hydrolysate component profiles and model substance analysis, phenolic compounds (especially lignin-derived H-unit monomers and phenolic acids) were confirmed to be the major tyrosinase inhibitors in hydrolysate. To further improve the inhibitory activity, an enrichment process of phenolic compounds by ethyl-acetate fractionation of hydrolysate was employed. Ethyl-acetate soluble fraction exhibited significantly enhanced anti-tyrosinase activity (IC50, 0.29 mg/mL), which was even better than p-coumaric acid (a typical tyrosinase inhibitor with IC50 of 0.31 mg/mL). Additionally, the mixed-type inhibition of hydrolysate on tyrosinase was illustrated by kinetics study and the interaction between hydrolysate and tyrosinase was confirmed by fluorescence quenching measurement. Consequently, this work aims to evaluate and improve the anti-tyrosinase activity of hydrolysate from steam explosion processing of corn stalk, which opens new perspectives in potential application of currently underused corn stalk hydrolysate as a value-added tyrosinase inhibitor.

Steam Explosion and Sequential Steam Explosion – Dilute Acid Pretreatment Optimization of Banana Pseudostem for Polyhydroxybutyrate (PHB) Production

Polyhydroxybutyrate (PHB) is a suitable biodegradable alternative to non-renewable petroleum-based plastics. Readily available agricultural lignocellulosic residues such as banana pseudostem can be utilized as a substrate to reduce the production cost of PHB and improve its feasibility for commercialization. Accordingly, pretreatment of banana pseudostem is needed to efficiently convert the substrate to PHB. In this study, optimization of two pretreatment methods for banana pseudostem – namely, steam explosion and sequential steam explosion – dilute acid pretreatment – were optimized to improve the digestibility of the biomass and consequently increase the production of reducing sugars in the hydrolysate during enzymatic saccharification. Response surface methodology (RSM)-designed experiments showed that among all factors investigated, for both pretreatment methods, the steam explosion temperature had the strongest positive impact on reducing sugar production. Optimum conditions of steam explosion pretreatment were 219.31 °C steam explosion temperature and 10 min of pretreatment time, producing 7.33 g/L (48.87% yield) of reducing sugars in the enzymatic hydrolysate. For sequential pretreatment, optimum conditions were 220 °C steam explosion temperature, 135 °C dilute acid temperature, 44 min of dilute acid reaction time, and 1.57% w/v H2SO4, with a corresponding reducing sugar concentration of 13.02 g/L (86.79% yield). A 90% increase in reducing sugar yield was observed after dilute acid pretreatment of steam-exploded banana pseudostem. Using the hydrolysate from sequentially-pretreated banana pseudostem, PHB (2.64 g/L) was successfully synthesized after 12 h of bacterial fermentation. Hence, sequential pretreatment was proven effective in producing enzymatic hydrolysates from banana pseudostem for PHB production.

Effect of steam explosion on physicochemical properties and fermentation characteristics of sorghum (Sorghum bicolor (L.) Moench)

Steam explosion (SE) was applied to modify the physicochemical properties and fermentation characteristics of sorghum (Sorghum bicolor (L.) Moench). Scanning electron microscopy (SEM) showed that the dense structures of sorghum especially the starch granules were destroyed, and much more folds, crimps and holes appeared in sorghum starch. Cellulose, hemicellulose and proteins in sorghum tended to decrease when the SE pressure increased which were investigated by fourier transformed infrared (FTIR) spectroscopy and SDS-PAGE. SE pretreatment increased the content of reducing sugar in sorghum, and the content of reducing sugar in sorghum pretreated by SE of 2.0 MPa increased over 19 times than the control. Moreover, fermentation results indicated that the ethanol yield was over 2 times higher than the control under the pressure of 1.5 MPa. The fermentation broth increased and the fermentation residue decreased obviously by SE pretreatment than the control. The kinds and the relative contents of esters increased, especially the ethyl acetate. This study suggested that SE pretreatment could reduce the waste content and promote the ethanol production in the liquor industry.

Bioethanol Production from Alkali Steam Explosion of Oil Palm of Empty Fruit Bunch Fiber

Bioethanol is the most promising biofuels and can be generated from lignocellulosic biomasses. The study of bioethanol production from oil palm empty fruit bunch (OPEFB) pretreated by alkali steam explosion was carried out employing separate enzymatic hydrolysis (SHF) and Simultaneous Saccharification and Fermentation (SSF) approaches. Alkaline extraction after steam explosion pretreatment of OPEFB led to the partial removal of lignin, hemicellulose and other degradation products from fiber surface. The pretreatment process is of great importance to ethanol yield. In the present study, the pretreatment was processed using a steam explosion reactor at 150°C, 4 bars for 30 minute with alkaline concentrations of NaOH 10% (kg/L). After pretreatment, the OPEFB substrates 10% and 15% (w/v) was saccharification using 30 FPU of Ctec2 and Htec2 enzyme and fermentation using yeast of Saccharomyces cerevisiae for 72 hours. The glucose obtained after 72 hours was 137.80 g/L (subtrate 15%) and 97.90 g/L (subtrate 10%). Bioethanol production in SSF mode faster and slightly more efficient process than SHF.

Preparation of rapeseed oil with superhigh canolol content and superior quality characteristics by steam explosion pretreatment technology.

In this study, rapeseed was pretreated by steam explosion pretreatment technology and subsequently pressed to prepare rapeseed oil. GC, UPLC, and HPLC techniques were employed to analyze the quality characteristics of the rapeseed oil, including the canolol content and other quality characteristics. Additionally, the effect of steam explosion pretreatment technology on the canolol content of rapeseed oil was studied and the formation mechanism of canolol elucidated. The results revealed that when the steam explosion pressure reached 1.0 MPa, the canolol content of the tested oil increased from 41.21 to 2,168.69 mg/kg (52.63‐fold increase) and that sinapic acid played a significant role in the conversion of canolol. Thus, the sinapine was converted into the intermediate (sinapic acid) by hydrolysis, which in turn was transformed into canolol through decarboxylation. The instantaneous high‐energy environment generated by steam explosion pretreatment could intensify the hydrolysis and decarboxylation reactions of sinapine and sinapinic acid, thereby significantly increasing the canolol content of the oil. To prove the superiority of steam explosion pretreatment, we compared it with other pretreatment technologies, including traditional high‐temperature roasting and popular microwave pretreatment. The results revealed that rapeseed oil prepared by steam explosion pretreatment displayed the best quality characteristics. This study can be a reference for the preparation process of rapeseed oil with superhigh canolol content and superior quality characteristics using steam explosion pretreatment.

Steam Explosion Pretreatment of Sludge for Pharmaceutical Removal and Heavy Metal Release to Improve Biodegradability and Biogas Production

Steam explosion pretreatment was developed and evaluated to remove pharmaceuticals and heavy metals from wastewater sludge and to improve its biodegradability and methane yield. Effects of pressure (5–15 bar) and duration (1–15 min) during the pretreatment were examined, and the pretreatment efficiency was evaluated based on the solubilization degree, the capillary suction time (CST) test and anaerobic digestion. The removal efficiency of ibuprofen, acetaminophen, and amoxicillin was 65%, 69%, and 66% and 70%, 66%, and 70% in primary sludge (PS) and waste-activated sludge (WAS), respectively. The highest percent release efficiency of heavy metals, i.e., lead, cadmium, and silver, for PS and WAS was 78%, 70%, and 79% and 79%, 80%, and 75%, respectively. The highest methane yield was obtained after pretreatment at 10 bar for 15 min and at 15 bar for 10 min, with respective yields of 380 and 358 mL CH4/g volatile solids (VS) for the PS and 315 and 334 mL CH4/g VS for the WAS. The results of methane production indicated that the decreased concentrations of pharmaceuticals and heavy metals resulted in increased biodegradability of PS and WAS.

Preparation of high-quality concentrated fragrance flaxseed oil by steam explosion pretreatment technology.

In this study, flaxseed was pretreated by steam explosion technology and subsequently pressed to prepare flaxseed oil. GC, UPLC, HPLC, and GC‐MS techniques were used to analyze the quality characteristics of the prepared flaxseed oil. These included the food safety risk indices, micronutrient components, and oxidative stability. The effects of different steam explosion pressures on the quality characteristics and relative volatile components of flaxseed oil were also investigated. The results revealed that steam explosion pretreatment technology could significantly increase the oil yield, improve micronutrient content, and strengthen the oxidation stability of the product. Moreover, the food safety risk indices (e.g., benzopyrene) were controlled within a reasonable range, while the fatty acid content remained almost unchanged. Notably, the relative pyrazine content in the total volatile components of flaxseed oil was 68.25% when the steam explosion pressure reached 1.2 MPa. This was considered as the main factor that contributed to the unique concentrated fragrance of the produced flaxseed oil. To prove the superiority of the steam explosion pretreatment, we compared this technique with traditional high‐temperature roasting and popular microwave pretreatment techniques. The results revealed that flaxseed oil prepared by steam explosion pretreatment displayed the best quality characteristics and most concentrated fragrance. Thus, steam explosion technology shows great potential for application to produce high‐quality concentrated fragrance flaxseed oil. This study provides significant reference and guidance for the preparation process of flaxseed oil.