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Biorefinery of Lignocellulosic Biomass

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A special issue of Fermentation (ISSN 2311-5637). This special issue belongs to the section "Industrial Fermentation".

Deadline for manuscript submissions: closed (15 July 2023) | Viewed by 25383

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Prof. Dr. Yaohua Zhong

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Guest Editor

State Key Laboratory of Microbial Technology, Institute of Microbial Technology, Shandong University, Jinan, China
Interests: cellulase; saccharification; filamentous fungus; strain improvement; fermentation
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Yinbo Qu

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Guest Editor

State Key Laboratory of Microbial Technology, Institute of Microbial Technology, Shandong University, Jinan, China
Interests: biorefinery; cellulose bioconversion; saccharification; fermentation

Special Issue Information

Dear Colleagues,

Lignocellulosic biomass is the most abundant and renewable material worldwide, thus making it a viable alternative to fossil fuels. Recent economic, energy, and even social–political factors have boosted the integral valorization of lignocellulosic biomass to facilitate moving from today’s fossil-based economy toward a bio-based economy. Biorefinery is the sustainable utilization of lignocellulosic biomass in a spectrum of commercial products, including biofuels and platform chemicals, to guarantee the highest profitability. However, there are still significant barriers in pretreatment, hydrolysis, and fermentation and its down-streaming processes, which have made commercialization difficult. The potent strains for the production of efficient enzymes and value-added byproducts are far from being thoroughly exploited. Optimization of feedstock pretreatment, enzymatic saccharification and sugar fermentation, together with integrated bioprocesses, remain the key to a biorefineries-based circular bioeconomy. Thus, a multidisciplinary approach to the valorization of lignocellulosic biomass would substantially accelerate progress in modern biorefineries and facilitate achieving commercial sustainability.

The present Special Issue aims to collect and publish both recent research results and review papers in the area of biorefineries based on lignocellulose for the production of biofuels and value-added byproducts. Actual studies addressing challenges in pretreatment, saccharification, fermentation, and integrated bioprocesses are of interest, but recent advances in the development of novel enzymes and microbial strains are also welcomed. If you would like to submit a review article, please contact one of the editors to discuss the relevance of the topic before writing your submission.

Prof. Dr. Yaohua Zhong
Prof. Dr. Yinbo Qu
Guest Editors

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Keywords

biorefinery
lignocellulosics
biofuels
value-added biochemicals
integrated bioprocess
pretreatment
cellulases
enzymatic hydrolysis
fermentable sugars
strain improvement

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Biorefinery of Lignocellulosic Biomass, 2nd Edition in Fermentation (1 article)

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Research

14 pages, 3191 KiB

Open AccessArticle

Metal Salt-Based Deep Eutectic Solvent Pretreatment of Moso Bamboo to Improve Enzymatic Hydrolysis

by Tianying Chen, Guixin Guo, Da Shen and Yanjun Tang

Fermentation 2023, 9(7), 618; https://doi.org/10.3390/fermentation9070618 - 29 Jun 2023

Cited by 5 | Viewed by 1479

Abstract

Research on metal salt-based deep eutectic solvent (DES) pretreatment is still in its infancy, and the effect of hydroxyl groups on Cl⁻ in choline chloride (ChCl) is not resolved. In this study, a type IV DES composed of metal salt and glycerol (Gly) was prepared for pretreatment of moso bamboo to improve its enzymatic hydrolysis. The correlation between enzymatic hydrolysis and the contents of hemicelluloses and lignin was evaluated using the Box–Behnken design. The results showed that FeCl₃-based DES was optimal among various DES. The solid recovery was reduced to 55.54% following FeCl₃/Gly pretreatment, which was effective in the removal of hemicelluloses and lignin compared with ternary DES pretreatment (with ChCl) under mild conditions (100 °C, 3 h). With the increase of pretreatment temperature (120 °C, 2 h), a significant proportion of hemicelluloses (76.07%) and lignin (62.77%) was removed. The structure of FeCl₃/Gly pretreatment residue was seriously damaged, and the glucose yield increased to 91.13% following enzymatic hydrolysis. This correlation indicated that the hemicelluloses’ content had a significant influence on enzymatic hydrolysis of the residue following FeCl₃/Gly pretreatment. This study elucidates the pretreatment effect of metal salt-based DES, which will be helpful in the value-added conversion of moso bamboo under mild conditions. Full article

(This article belongs to the Special Issue Biorefinery of Lignocellulosic Biomass)

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14 pages, 3414 KiB

Open AccessArticle

Fermentative L-Lactic Acid Production Using Bacillus coagulans from Corn Stalk Deconstructed by an Anaerobic Microbial Community

by Xu Yang, Zhiyuan Shi, Tongyu Wang, Xiangyu Meng, Lili Song, Zhiping Zhang, Jingnan Zhang and Tao Wei

Fermentation 2023, 9(7), 611; https://doi.org/10.3390/fermentation9070611 - 28 Jun 2023

Cited by 2 | Viewed by 2350

Abstract

This study investigated the feasibility of producing L-lactic acid (LA) from dry corn stalk (DCS) that was pretreated by ensiling by an anaerobic microbial community consisting of Bacillus coagulans, Lactobacillus fermentum, and Enterococcus durans. After 28 days of ensiling, the LA and acetic acid content in the microsilage was 2.04 ± 0.08% and 0.38 ± 0.01%, respectively, and the pH was 4.47 ± 0.13. Enterococcus and Lactobacillus became the dominant microbiota during the ensiling process. Twenty-eight-day-old microsilage was then subjected to fermentation by B. coagulans to produce LA in a simultaneous saccharification and co-fermentation process. The enzymatic hydrolysis yield reached >96%. The maximal concentration of LA reached 18.54 ± 0.52 g/L with a substrate concentration of 5%, where the yield of LA was 0.31 ± 0.01 g/g DCS and the optical purity of the product LA was >97%. Anaerobic ensiling is viable for the pretreatment of biomass for the production of value-added chemicals. Full article

(This article belongs to the Special Issue Biorefinery of Lignocellulosic Biomass)

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17 pages, 3097 KiB

Open AccessArticle

Improving Pulping Performance as Well as Reducing Consumption and Increasing Efficiency via Microbial Consortium Pretreating Bamboo

by Chun Liu, Zhijian Li, Xiuqiong Guan, Yang Xu, Nan Huang and Kui Liu

Fermentation 2023, 9(4), 400; https://doi.org/10.3390/fermentation9040400 - 20 Apr 2023

Cited by 1 | Viewed by 1938

Abstract

The bio-refining process of bamboo is more challenging compared to wood due to its dense and stabilized complex polymer structure, as well as its abundance of degradation-resistant components. Consequently, the bio-refining of bamboo requires more energy and time consumption compared to the bio-refining of wood. In this study, co-cultured microorganisms were utilized for the pretreatment of bamboo to improve pulping performance, reduce consumption, and increase efficiency. These microorganisms were constructed by combining environmental microorganisms found in bamboo pulp with Bacillus sp. that were self-screened. The results of 16S rRNA analysis showed that the genera Proteobacteria, Firmicutes, Bacteroidota, and Actinobacteriota gradually became dominant during the treatment process. Additionally, the PICRUSt results indicated that the co-culture microbial consortium C strategy strengthened key enzyme activities related to the degradation of bamboo lignocelluloses. The microbial consortium pretreatment resulted in removing lignin and hemicellulose at rates of 21.96% and 26.21%, respectively. This process also caused a decrease in the crystalline index, indicating the presence of disordered crystalline regions. This change was beneficial for the subsequent Kraft pulping process. Compared to the conventional bamboo pulp, the yield of pretreated bamboo pulp increased slightly, while the cellulose purity and paper properties were significantly superior. The obtained Kraft pulp, which underwent microbiological pretreatment, met the requirements for superior Kraft pulp products despite a 65 min decrease in cooking time and a 10 °C decline in maximum cooking temperature. This study proves that co-cultured microbial consortium used for pretreating bamboo are beneficial for bamboo Kraft pulping. This approach can be considered environmentally friendly and leads to energy saving and cost reduction in bamboo bio-refining processes. Full article

(This article belongs to the Special Issue Biorefinery of Lignocellulosic Biomass)

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17 pages, 3153 KiB

Open AccessArticle

Overexpression of a Novel Vacuolar Serine Protease-Encoding Gene (spt1) to Enhance Cellulase Production in Trichoderma Reesei

by Cheng Yao, Ningning Sun, Weihao Gao, Yu Sun, Jiaxin Zhang, Hong Liu and Yaohua Zhong

Fermentation 2023, 9(2), 191; https://doi.org/10.3390/fermentation9020191 - 19 Feb 2023

Cited by 3 | Viewed by 2198

Abstract

Trichoderma reesei is widely applied as the major industrial fungus for the production of cellulases used for the conversion of lignocellulosic biomass to biofuels and other biobased products. The protein secretion pathway is vital for cellulase secretion, but few reports are related to the role of the vacuole in cellulase production. Here, we identified a novel vacuolar serine protease gene spt1 and investigated the ability of T. reesei to secrete cellulases by disrupting, complementing and overexpressing the spt1 gene. Amino acid sequence analysis of the Spt1 protein showed that it belongs to the subtilisin S8 family and has the conserved catalytic triples (Asp, His, Ser) of the serine protease. The deletion of spt1 did not lead to a decrease in extracellular protease activity, and the observation of mycelia with the Spt1–eGFP fusion expression and the vacuolar membrane dye FM4-64 staining confirmed that Spt1 was an intracellular protease located in the vacuoles of T. reesei. However, the spt1 gene deletion significantly reduced spore production and cellulase secretion, while the spt1 complementation recovered these traits to those of the parental strain. When spt1 was overexpressed by using its native promoter and introducing multiple copies, the cellulase secretion was improved. Furthermore, a strong promoter, Pcdna1, was used to drive the spt1 overexpression, and it was found that the cellulase production was significantly enhanced. Specifically, the filter paper activity of the spt1 overexpression strain SOD-2 reached 1.36 U/mL, which was 1.72 times higher than that of the parental strain. These findings demonstrated that the spt1 gene can be a powerful target for increasing cellulase production in T. reesei, which suggests a possible important role of the vacuole in the cellulase secretion pathway and provides new clues for improving strains for efficient cellulase production. Full article

(This article belongs to the Special Issue Biorefinery of Lignocellulosic Biomass)

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19 pages, 6605 KiB

Open AccessArticle

A Chemical-Free Pretreatment for Biosynthesis of Bioethanol and Lipids from Lignocellulosic Biomass: An Industrially Relevant 2G Biorefinery Approach

by Narendra Naik Deshavath, Bruce S. Dien, Patricia J. Slininger, Yong-Su Jin and Vijay Singh

Fermentation 2023, 9(1), 5; https://doi.org/10.3390/fermentation9010005 - 21 Dec 2022

Cited by 4 | Viewed by 2757

Abstract

A wide range of inorganic and organic chemicals are used during the pretreatment and enzymatic hydrolysis of lignocellulosic biomass to produce biofuels. Developing an industrially relevant 2G biorefinery process using such chemicals is challenging and requires more unit operations for downstream processing. A sustainable process has been developed to achieve industrially relevant titers of bioethanol with significant ethanol yield. The pretreatment of sorghum biomass was performed by a continuous pilot-scale hydrothermal reactor followed by disk milling. Enzymatic hydrolysis was performed without washing the pretreated biomass. Moreover, citrate buffer strength was reduced to 100-fold (50 mM to 0.5 mM) during the enzymatic hydrolysis. Enzymatic hydrolysis at 0.5 mM citrate buffer strength showed that significant sugar concentrations of 222 ± 2.3 to 241 ± 2.3 g/L (glucose + xylose) were attained at higher solids loadings of 50 to 60% (w/v). Furthermore, hydrolysates were fermented to produce bioethanol using two different xylose-fermenting Saccharomyces cerevisiae strains and a co-culture of xylose-fermenting and non-GMO yeast cultures. Bioethanol titer of 81.7 g/L was achieved with an ethanol yield of 0.48 g_p/g_s. Additionally, lipids were produced using the oleaginous yeast Rhodosporidium toruloides, yielding 13.2 g/L lipids with cellular lipid accumulation of 38.5% w/w from 100 g/L of sugar concentration. In summary, reducing the strength of the citrate buffer during enzymatic hydrolysis and omitting inorganic chemicals from the pretreatment process enhances the fermentability of hydrolysates and can also reduce operating costs. Full article

(This article belongs to the Special Issue Biorefinery of Lignocellulosic Biomass)

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24 pages, 3749 KiB

Open AccessArticle

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

by Pradeep Kumar Gandam, Madhavi Latha Chinta, A. Priyadarshini Gandham, Ninian Prem Prashanth Pabbathi, Srilekha Konakanchi, Anjireddy Bhavanam, Srinivasa R. Atchuta, Rama Raju Baadhe and Ravi Kant Bhatia

Fermentation 2022, 8(12), 704; https://doi.org/10.3390/fermentation8120704 - 3 Dec 2022

Cited by 20 | Viewed by 5977

Abstract

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. Full article

(This article belongs to the Special Issue Biorefinery of Lignocellulosic Biomass)

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11 pages, 3071 KiB

Open AccessArticle

Kinetic Modeling of an Enzyme Membrane Reactor for the Selective Production of Oligosaccharides

by Shusaku Asano, Yosuke Muranaka, Taisuke Maki, Koki Ikeda and Kazuhiro Mae

Fermentation 2022, 8(12), 701; https://doi.org/10.3390/fermentation8120701 - 2 Dec 2022

Cited by 2 | Viewed by 2023

Abstract

An enzyme membrane reactor is an attractive tool for producing oligosaccharides from biomass-based polysaccharides. However, kinetic modeling and reactor design based on the rate equations have rarely been reported for enzyme membrane reactors because of the difficulty in tracing the depolymerization process. In this study, a simplified reaction model based on Michaelis–Menten-type kinetics has been built to simulate the enzyme membrane reactor. Ramping various species into reactant, target, and byproduct worked well for discussing reactor performance. The use of a membrane with a molecular weight cut-off (MWCO) of 10 kDa with continuous feeding of the reactant was suggested for the efficient production of chitosan hexamer and pentamer by enzymatic hydrolysis of chitosan. Full article

(This article belongs to the Special Issue Biorefinery of Lignocellulosic Biomass)

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15 pages, 3490 KiB

Open AccessArticle

Efficient Corncob Biorefinery for Ethanol Initiated by a Novel Pretreatment of Densifying Lignocellulosic Biomass with Sulfuric Acid

by Shuangmei Liu, Yang Yu, Zhaoxian Xu, Sitong Chen, Guannan Shen, Xinchuan Yuan, Qiufeng Deng, Wenyuan Shen, Shizhong Yang, Chengcheng Zhang, Xiangxue Chen and Mingjie Jin

Fermentation 2022, 8(11), 661; https://doi.org/10.3390/fermentation8110661 - 21 Nov 2022

Cited by 13 | Viewed by 2679

Abstract

Corncob is a potential feedstock for biorefineries to produce cellulosic ethanol and other chemicals. Densifying lignocellulosic biomass with chemicals followed by autoclave (DLCA) has been confirmed an efficient and economical pretreatment method, and it was applied in the present work for conversion of corncob to bioethanol. The dosage of sulfuric acid, solid loading of biomass, and autoclave time for pretreatment were investigated. Enzymatic hydrolysis at 25–35% solids loadings resulted in 91–97% sugar conversions. Fermentation of the resulted hydrolysates went well with the highest ethanol titer reaching 75.71 g/L at 35% solid loading. Simultaneous saccharification and co-fermentation was applied to further improve xylose consumption at high solids loadings and the ethanol titer was enhanced to 82.0 g/L at 35% solid loading with an ethanol yield of 21.67 kg/100 kg corncob. This study demonstrated DLCA provided a highly digestible and highly fermentable corncob for biorefinery. Full article

(This article belongs to the Special Issue Biorefinery of Lignocellulosic Biomass)

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13 pages, 1413 KiB

Open AccessArticle

Plant Proteins as an Alternative Nitrogen Source for Chiral Purity L-Lactic Acid Fermentation from Lignocellulose Feedstock

by Bin Zhang, Lei Wu, Xiucai Liu and Jie Bao

Fermentation 2022, 8(10), 546; https://doi.org/10.3390/fermentation8100546 - 16 Oct 2022

Cited by 6 | Viewed by 2678

Abstract

High optical purity lactic acid is in high demand as the precursor for synthesizing polylactic acid (PLA). The costs of expensive carbohydrates and nitrogen source materials accounts for a large portion of the production costs in lactic homo-fermentation. The use of lignocellulosic biomass for lactic acid production reduces the cost of the carbohydrate feedstock, but the cost of nitrogen sources is a big challenge when considering the high prices of general nitrogen sources. Low-cost nitrogen materials are vulnerable to being contaminated by exogenous mixed L-lactic acid and D-lactic acid; thus, their feasibility as nitrogen sources for the production of optically pure lactic acid products is hindered. The available reports focus on cost reduction using agro-industrial byproducts as nutrient sources, with these presenting fewer concerns on the effect of the optical purity of lactic acid-product monomers for polymerization. In this study, commonly used low-cost nutrient sources were characterized and screened for high optical purity L-lactic acid fermentation. Corn steep liquor (CSL), a widely used and cheap nutrient for lactic acid fermentation, was found not to be suitable because of its high content of mixed D-/L-lactic acids (up to 20%, w/w). On the other hand, cottonseed meal was found to be completely free of mixed L-/D-lactic acids. Therefore, the cottonseed meal was hydrolyzed with dilute sulfuric acid and used as a nitrogen source for L-lactic acid fermentation using lignocellulose feedstock as a substitution for yeast extract and peptone. The results showed that the final L-lactic acid titer reached 96.5 ± 0.2 g/L from 25% (w/w)-solids loaded pretreated and biodetoxified wheat straw with a yield of 0.31 g/g feedstock and an optical purity of 99.7%. The techno-economic evaluation indicated that the cost of the cottonseed meal was only USD 0.193/kg of lactic acid product, and the minimum lactic acid selling price (MLSP) was USD 0.813/kg of lactic acid product, which was only 25.1% compared to the use of yeast extract and peptone as the nutrients. Cellulosic L-lactic acid production using cottonseed meal as a complex nutrient source showed competitive performance when compared to starch feedstock from food crops. Full article

(This article belongs to the Special Issue Biorefinery of Lignocellulosic Biomass)

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