Factors affecting cellulose and hemicellulose hydrolysis of alkali treated brewers spent grain by Fusarium oxysporum enzyme extract

Successive process for efficient biovalorization of Brewers' spent grain to lignocellulolytic enzymes and lactic acid production through simultaneous saccharification and fermentation

This study aimed to increase the value of brewers' spent grain (BSG) by using it as feedstock to produce lignocellulolytic enzymes and lactic acid (LA). Twenty-two fungal strains were screened for lignocellulolytic enzyme production from BSG. Among them, Trichoderma sp. showed the highest cellulase activity (35.84 ± 0.27 U/g-BSG) and considerably high activities of xylanase (599.61 ± 23.09 U/g-BSG) and β-glucosidase (16.97 ± 0.77 U/g-BSG) under successive solid-state and submerged fermentation. The processes were successfully scaled up in a bioreactor. The enzyme cocktail was recovered and characterized. The maximum cellulase and xylanase activities were found at pH 5.0 and 50 °C, and the activities were highly stable at pH 4-8 and 30-50 °C. The enzyme cocktail was applied in simultaneous saccharification and fermentation of acid-pretreated BSG for LA production. The maximum LA obtained was 59.3 ± 1.0 g/L. This study has shown the efficient biovalorization of BSG, and this approach may also be applicable to other agro-industrial wastes.

Production of xylose through enzymatic hydrolysis of glucuronoarabinoxylan from brewers' spent grain

Xylose is an abundant bioresource for obtaining diverse chemicals and added-value products. The production of xylose from green alternatives like enzymatic hydrolysis is an important step in a biorefinery context. This research evaluated the synergism among four classes of hydrolytic purified enzymes-endo-1,4-β-xylanase, α-L-arabinofuranosidase, β-xylosidase, and α-D-glucuronidase-over hydrolysis of glucuronoarabinoxylan (GAX) obtained from brewers' spent grain (BSG) after alkaline extraction and ethanol precipitation. First, monosaccharides, uronic acids and glycosidic-linkages of alkaline extracted GAX fraction from BSG were characterized, after that different strategies based on the addition of one or two families of enzymes-endo-1,4-β-xylanase (GH10 and GH11) and α-L-arabinofuranosidase (GH43 and GH51)-cooperating with one β-xylosidase (GH43) and one α-D-glucuronidase (GH67) into enzymatic hydrolysis were assessed to obtain the best yield of xylose. The xylose release was monitored over time in the first 90 min and after a prolonged reaction up to 48 h of reaction. The highest yield of xylose was 63.6% (48 h, 40 ℃, pH 5.5), using a mixture of all enzymes devoid of α-L-arabinofuranosidase (GH43) family. These results highlight the importance of GH51 arabinofuranosidase debranching enzyme to allow a higher cleavage of the xylan backbone of GAX from BSG and their synergy with 2 endo-1,4-β-xylanase (GH10 and GH11), one β-xylosidase (GH43) and the inclusion of one α-D-glucuronidase (GH67) in the reaction system. Therefore, this study provides an environmentally friendly process to produce xylose from BSG through utilization of enzymes as catalysts.

Brewers' spent grain liquor as a feedstock for lactate production with Lactobacillus delbrueckii subsp. lactis

Brewers' spent grain (BSG) is a low-cost by-product of the brewing process. BSG liquor names the liquid components of BSG, mainly glucose, maltose, and long-chain α-1,4-glycosidic bond glucose oligomers. These substances should be separated in existing BSG biorefineries, as they might lead to an increased formation of microbe-inhibiting compounds in well-established hydrothermal/enzymatic saccharification processes. In most cases, this liquid fraction is discarded. The present study presents for the first time an optimized process with BSG liquor for the purpose of producing bulk chemicals (e.g., lactate) in relevant concentrations. The process comprises the application of yeast extract, produced from own brewing processes, as the sole supplemented complex constituent in a simultaneous fermentation and saccharification process. Kinetic parameters for the final optimized process conditions with the organism Lactobacillus delbrueckii subsp. lactis were: maximum specific growth rate µmax  =  0.47 h-1, maximum lactate concentration cLac, max  =  79.06 g L-1, process yield YPS  =  0.89 gLac gSugar -1, lactate production rate qP  =  4.18 gLac gCDW -1 h-1, and productivity P 15 h  =  4.93 gLac L-1 h-1. BSG liquor, linked with yeast extract from Brewers' yeast, can be a promising substrate for further bioprocess engineering tasks and contribute to a holistic and sustainable usage of Brewers' spent grain.

A Multispecies Fungal Biofilm Approach to Enhance the Celluloyltic Efficiency of Membrane Reactors for Consolidated Bioprocessing of Plant Biomass

The constraints and advantages in cellulolytic enzymes production by fungal biofilms for a consolidated bioconversion process were investigated during this study. The biofilm cultivations were carried out in reactors designed for consolidated bioprocessing Multispecies Biofilm Membrane reactors, (MBM) where an aerobic fungal biofilm produces the lignocellulolytic enzymes while a fermenting microorganism forms the fermentation product at anaerobic conditions. It was shown that although mycelial growth was limited in the MBM reactors compared to submerged cultivations, the secretion of cellulolytic enzymes per cell dry weight was higher. When Trichoderma reesei was used as the sole enzyme producer, cellobiose accumulated in the liquid medium as the result of the deficiency of β-glucosidase in the fungal secretome. To enhance β-glucosidase activity, T. reesei was co-cultivated with A. phoenicis which is a β-glucosidase overproducer. The two fungi formed a multispecies biofilm which produced a balanced cellulolytic cocktail for the saccharification of plant biomass. The mixed biofilm reached a 2.5 fold increase in β-glucosidase production, compared to the single T. reesei biofilm. The enzymatic systems of single and mixed biofilms were evaluated regarding their efficiency on cellulosic substrates degradation. Washed solids from steam pretreated beechwood, as well as microcrystalline cellulose were used as the substrates. The enzymatic system of the multispecies biofilm released four times more glucose than the enzymatic system of T. reesei alone from both substrates and hydrolyzed 78 and 60% of the cellulose content of washed solids from beechwood and microcrystalline cellulose, respectively.

Feasibility of a facile butanol bioproduction using planetary mill pretreatment

A facile butanol bioproduction process was developed using planetary milling, and Pinus rigida wood waste as a model substrate for fermentable sugars. The use of planetary milling as the pretreatment eliminates the need for washing and transfer of the biomass prior to enzymatic hydrolysis. Moreover, using this pretreatment process resulted in the production of only 0.072 ± 0.003 g/L soluble phenolic compounds, a concentration that was not inhibitory towards Clostridium beijerinckii NCIMB 8052. As the milling was performed in a compatible buffer (50mM acetate, pH 4.8), the enzymatic hydrolysis step was initiated by simply adding the cellulase cocktail powder directly to pretreated biomass without washing the biomass or exchanging the buffer, resulting in a glucose yield of 31 g/L (84.02%). Fermentation of the hydrolysate samples by C. beijerinckii NCIMB 8052 gave slightly better butanol yields than cultures grown in a typical lab media (P2), with final concentrations of 6.91 and 6.66 g/L, respectively.

Challenges in ethanol production with Fusarium oxysporum through consolidated bioprocessing

Fusarium oxysporum has been reported as being able to both produce the enzymes necessary to degrade lignocellulosic biomass to sugars and also ferment the monosaccharides to ethanol under anaerobic or microaerobic conditions. However, in order to become an economically feasible alternative to other ethanol-producing microorganisms, a better understanding of its physiology, metabolic pathways, and bottlenecks is required, together with an improvement in its efficiency and robustness. In this report, we describe the challenges for the future and give additional justification for our recent publication.

Exploring pathogenic mechanisms of Botrytis cinerea secretome under different ambient pH based on comparative proteomic analysis

Botrytis cinerea causes gray mold rot on over 200 plant species worldwide, resulting in great economic loss every year. Cooperation of proteins secreted by B. cinerea plays an important role in its successful infection to host plants. The ambient pH, as one of the most important environmental parameters, can regulate expression of secreted proteins in various fungal pathogens. In the present study, we mainly investigated the effect of ambient pH on secretome of B. cinerea strain B05.10 with a comparative proteomic method based on 2-DE. Distinct differences in secretome of B. cinerea were found between pH 4 and 6 treatments, and 47 differential spots, corresponding to 21 unique proteins, were identified using MALDI-TOF/TOF. At pH 4, more proteins related to proteolysis were induced, whereas most of up-accumulated proteins were cell wall degrading enzymes at pH 6. Analysis of gene expression using quantitative real-time PCR suggests that production of most of these proteins was regulated at the level of transcription. These findings indicate that B. cinerea can adjust protein profile of secretome responding to different ambient pH values and provide evidence to deeply understand the complicated infecting mechanisms of B. cinerea on a wide range of plant hosts.