Optimizing tri-acid mixture hydrolysis: An improved strategy for efficient xylooligosaccharides production from corncob.

Propionic acid (PA) hydrolysis of corncob for xylooligosaccharides (XOS) production has the advantages of simple operation, high XOS yield and less by-products, but the high price of PA limits its application. Therefore, partially replacing PA with less expensive organic acids, such as formic acid (FA) and acetic acid (AC), may lower the cost of hydrolysis in XOS production. This work investigated the feasibility of XOS production from corncob using a tri-acid mixture of FA, AC and PA. A high XOS yield of 69.1 % was achieved under the optimal FA:PA:AC volume ratio of 1:5:4 at 150 °C for 50 min. Overall, in the XOS production from corncob, it was able to replace 60 % of PA with FA and AC, and decreased the hydrolysis temperature from 170 °C to 150 °C, all of which were important to lower the cost of XOS production using organic acid hydrolysis.

Mapping the field of microalgae CO2 sequestration: a bibliometric analysis.

Microalgae CO2 sequestration has gained considerable attention in the last three decades as a promising technology to slow global warming caused by CO2 emissions. To provide a comprehensive and objective analysis of the research status, hot spots, and frontiers of CO2 fixation by microalgae, a bibliometric approach was recently chosen for review. In this study, 1561 articles (1991-2022) from the Web of Science (WOS) on microalgae CO2 sequestration were screened. A knowledge map of the domain was presented using VOSviewer and CiteSpace. It visually demonstrates the most productive journals (Bioresource Technology), countries (China and USA), funding sources, and top contributors (Cheng J, Chang JS, and their team) in the field of CO2 sequestration by microalgae. The analysis also revealed that research hotspots changed over time and that recent research has focused heavily on improving carbon sequestration efficiency. Finally, commercialization of carbon fixation by microalgae is a key hurdle, and supports from other disciplines could improve carbon sequestration efficiency.

Enhanced photoautotrophic growth of Chlorella vulgaris in starch wastewater through photo-regulation strategy.

Microalgae biomass production with starch wastewater (SW) is a promising approach to realize waste recovery and cost reduction due to the inherent copious nutrients and nontoxic compounds in SW. However, the application of this technique is significantly hindered by low biomass production on account of the poor photosynthetic efficiency of microalgae. In this regard, we proposed a photo-regulation strategy characterized by the adjusting of numbers of light/dark (L/D) cycles, and compositions of light wavelength, which was proved to be an effective method for stimulating intracellular photo electron transfer and enhancing photosynthetic efficiency, to boost microalgae biomass accumulation. Additionally, responses of the microalgae photo-biochemical conversion, and the wastewater treatment performance at various number of L/D cycles and light wavelengths were discussed. The experimental results indicated that the biomass production increased when the L/D period was increased from 2 h:2 h-12 h:12 h. When the L/D period was 2 h:2 h, the biomass production reached a maximum value of 1.28 g L-1, which was 19.6% higher than that of the control group when the L/D period was 12 h:12 h. Furthermore, with respect to microalgae growth under monochromatic light, the maximum biomass concentration (1.25 g L-1) and lipid content (32.2%) of Chlorella were achieved under blue light; whereas, the minimum values were attained under red light (1.05 g L-1 and 19.3%, respectively). When the red light and blue light were mixed and supplied, the microalgae biomass productivity was higher than that under white light, and the highest lipid productivity was 109.0 mg-1 L-1 d under a blue: red ratio of 2:1. Moreover, gas chromatography analysis demonstrated that the methyl in the range of C16-C18 in the system was higher than 70%. Fatty acid methyl esters (FAMEs) containing palmitic acid (C16:0) and oleic acid (C18:1) are beneficial for production of biodiesel, and the quality of fatty acid methyl ester used in biodiesel production can be improved using microalgae cultured under the mixed wavelengths of blue and red. Finally, Chlorella was cultured in PBR and reached the peak concentration of 2.45 g L-1 by semi-continuous process with the HRT regulation.

Mild fractionation of sugarcane bagasse into fermentable sugars and ß-O-4 linkage-rich lignin based on acid-catalysed crude glycerol pretreatment.

Acid-catalysed crude glycerol (ACG) pretreatment was carried out at 110 °C and 130 °C for mild fractionation of sugarcane bagasse into fermentable sugars and high-quality lignin. ACG pretreatment at 110 °C led to sugar yields of 71%-74%, comparable to those with acid-catalysed reagent-grade glycerol (AG). ACG pretreatment removed more lignin (53%-75%) than AG pretreatment (38%-49%), likely due to the presence of organic impurities in ACG. Hence, 28% more lignin was recovered from ACG pretreatment hydrolysate than with the AG pretreatment. NMR analysis revealed that recovered lignin was modified by glycerol through etherification of ß-aryl ethers and esterification of hydroxycinnamic acids, which prevented lignin condensation and led to the generation of ß-O-4 linkage-rich lignin at mild conditions (110 °C for 3 h and 5 h). This study suggests that crude glycerol is a suitable low-cost solvent for mild fractionation of lignocellulosic biomass into fermentable sugars and high-quality lignin for value-adding applications.

Mild Acid-Catalyzed Atmospheric Glycerol Organosolv Pretreatment Effectively Improves Enzymatic Hydrolyzability of Lignocellulosic Biomass.

Conventional atmospheric glycerol organosolv pretreatment is energy-intensive with the requirement of long time and/or high temperature. Herein, acid-catalyzed atmospheric glycerol organosolv (ac-AGO) pretreatment was developed under a mild condition to modify the sugarcane bagasse structure for improving enzymatic hydrolyzability. Using single factor and central composite design experiments, ac-AGO pretreatment was optimized at 200 °C for 15 min with 0.06% H2SO4 addition, wherein the hemicellulose and lignin removal rates were 82 and 52%, respectively, with extremely high cellulose retention of 98%. The ac-AGO-pretreated substrate exhibited good enzymatic hydrolyzability at a modest cellulase loading, affording a 70% glucose yield after 72 h. Multiple analysis tools were used to correlate the hydrolyzability of the substrate with its structural features. The results indicated that the mild ac-AGO pretreatment can modify the lignocellulosic biomass structure to achieve good hydrolyzability, mainly resulting in significant hemicellulose removal.

Bioprocessing of tea oil fruit hull with acetic acid organosolv pretreatment in combination with alkaline H2O2.

BACKGROUND: As a natural renewable biomass, the tea oil fruit hull (TOFH) mainly consists of lignocellulose, together with some bioactive substances. Our earlier work constructed a two-stage solvent-based process, including one aqueous ethanol organosolv extraction and an atmospheric glycerol organosolv (AGO) pretreatment, for bioprocessing of the TOFH into diverse bioproducts. However, the AGO pretreatment is not as selective as expected in removing the lignin from TOFH, resulting in the limited delignification and simultaneously high cellulose loss. RESULTS: In this study, acetic acid organosolv (AAO) pretreatment was optimized with experimental design to fractionate the TOFH selectively. Alkaline hydrogen peroxide (AHP) pretreatment was used for further delignification. Results indicate that the AAO-AHP pretreatment had an extremely good selectivity at component fractionation, resulting in 92% delignification and 88% hemicellulose removal, with 87% cellulose retention. The pretreated substrate presented a remarkable enzymatic hydrolysis of 85% for 48 h at a low cellulase loading of 3 FPU/g dry mass. The hydrolyzability was correlated with the composition and structure of substrates by using scanning electron microscopy, confocal laser scanning microscopy, and X-ray diffraction. CONCLUSION: The mild AAO-AHP pretreatment is an environmentally benign and advantageous scheme for biorefinery of the agroforestry biomass into value-added bioproducts.

Industrially relevant hydrolyzability and fermentability of sugarcane bagasse improved effectively by glycerol organosolv pretreatment.

BACKGROUND: Previous work has demonstrated that glycerol organosolv pretreatment can effectively improve the hydrolyzability of various lignocellulosic substrates. This pretreatment process strategy is ideal to integrate a commercially successful lignocellulosic and vegetable oil biorefinery industry. However, industrially relevant high-solid-loading hydrolyzability and fermentability of the pretreated substrates have yet to be considered for enzyme-based lignocellulosic biorefineries. RESULTS: In this study, an AGO pretreatment of sugarcane bagasse was evaluated with regard to the component selectivity, structural modification, hydrolyzability, and fermentation of pretreated substrates. The results showed that the AGO pretreatment presented good component selectivity, removing approximately 70 % lignin and hemicellulose, respectively, from sugarcane bagasse with a near-intact preservation (94 %) of the overall cellulose. The pretreatment deconstructed the recalcitrant architecture of natural lignocellulosic biomass, thereby modifying the structure at the macro-/micrometer level (fiber size, surface area, average size, roughness) and supermolecular level (key chemical bond dissociation) of lignocellulosic substrates towards good hydrolyzability. Notably, extraordinarily few fermentation inhibitors (<0.2 g furfural and 5-hydromethyl furfural/kg feedstock) were generated from the AGO pretreatment process, which was apparently due to the prominent role of glycerol organic solvent in protecting monosaccharides against further degradation. The 72-h enzymatic hydrolysis of pretreated substrates at 15 % solid content achieved 90 % completion with Cellic CTec2 at 10 FPU/g dried substrate. With a simple nutrition (only 10 g/L (NH4)2SO4) addition, the fed-batch semi-SSF of AGO-pretreated substrates (30 % solid content) almost reached 50 g/L ethanol with cellulase preparation at 10 FPU/g dried substrate. These results have revealed that the pretreated substrate is susceptible and accessible to cellulase enzymes, thereafter exhibiting remarkable hydrolyzability and fermentability. CONCLUSION: The AGO pretreatment is a promising candidate for the current pretreatment process towards industrially relevant enzyme-based lignocellulosic biorefineries.

Heterologous expression of codon optimized Trichoderma reesei Cel6A in Pichia pastoris.

The Cel6A deficiency has become one of the limiting factors for cellulose saccharification in biochemical conversion of cellulosic biomass to fuels and chemicals. The work attempted to use codon optimization to enhance Trichoderma reesei Cel6A expression in Pichia pastoris. Two recombinants P. pastoris GS115 containing AOX1 and GAP promotors were successfully constructed, respectively. The optimal temperatures and pHs of the expressed Cel6A from two recombinants were consistent with each other, were also in the extremely similar range to that reported on the native Cel6A from T. reesei. Based on the shake flask fermentation, AOX1 promotor enabled the recombinant to produce 265U/L and 300mg/L of the Cel6A enzyme, and the GAP promotor resulted in 145U/L and 200mg/L. High cell density fed batch (HCDFB) fermentation significantly improved the enzyme titer (1100U/L) and protein yield (2.0g/L) for the recombinant with AOX1 promotor. Results have showed that the AOX1 promotor is more suitable than the GAP for the Cel6A expression in P. pastoris. And the HCDFB cultivation is a favorable way to express the Cel6A highly in the methanol inducible yeast.

The impact of glycerol organosolv pretreatment on the chemistry and enzymatic hydrolyzability of wheat straw.

Given that the glycerol organosolv pretreatment (GOP) can effectively improve the hydrolyzability of various lignocellulosic substrates, physicochemical changes of the substrate before and after the pretreatment was characterized to elucidate what is responsible for it. The effect of GOP on the main components and hydrolyzability of wheat straw was revisited. Results demonstrate that the GOP should be a promising candidate for the current pretreatment. Then the composition and structure of substrates was measured at multi-dimensional scales by using various analytic equipment such as TGA, SEM, AFM, CLSM, FT-IR, XRD and solid-state CP/MAS (13)C NMR. This paper reports some new insights on the mechanism behind that, which can be beneficial for further development, optimization, and scale-up of the GOP process.