Biobutanol production from brewer's spent grain hydrolysates by Clostridium beijerinckii

Soy whey and brewer's spent grain hydrolysates wholly replace conventional medium for microalgae growth: Process performance and economic considerations

To enhance circularity in heterotrophic microalgal bioprocesses, this study completely substituted glucose and Bold's basal medium (BBM) with brewer's spent grain (BSG) and soy whey (SW) hydrolysates. Mild acid hydrolysis conditions of BSG (0.2 M H2SO4, 130 °C, 36 min) and SW (0.1 M HCl, 95 °C, 30 min) were optimised for glucose release, and their hydrolysates were optimally mixed (15 % SW-85 % BSG) to obtain a medium that best supported Auxenochlorella protothecoides growth. Maximum biomass production (Xmax) and productivity (PXmax) obtained in the hydrolysate medium containing 50.75 g/L endogenous glucose (Xmax: 22.17 g/L; PXmax: 7.06 g/L/day) were comparable to that in BBM containing 50.44 g/L exogenous glucose (Xmax: 20.02 g/L; PXmax: 6.34 g/L/day). Moreover, estimated hydrolysate medium production costs were within an order of magnitude to BBM. Overall, the integrated approach of tailored hydrolytic treatments and complementary side-streams presents a promising technical and economic feasibility, with applications extending beyond A. protothecoides.

Recent advances in microbial high-value utilization of brewer's spent grain

Mitigating the adverse impacts of agricultural and industrial by-products on human populations and the environment is essential. It is crucial to continually explore methods to upgrade and reengineer these by-products. Brewer's Spent Grain (BSG), the primary by-product of the beer brewing process, constitutes approximately 85% of these by-products. Its high moisture content and rich nutritional profile make BSG a promising candidate for microbial utilization. Consequently, valorizing high-yield, low-cost BSG through microbial fermentation adds significant value. This paper provides a comprehensive overview of two valorization pathways for BSG via microbial processing, tailored to the desired end products: utilizing fermented BSG as a nutritional supplement in human or animal diets, or cultivating edible fungi using BSG as a substrate. The review also explores the microbial fermentation of BSG to produce valuable metabolites, laying a theoretical foundation for its high-value utilization.

Review of the valorization initiatives of brewing and distilling by-products

Beer and spirits are two of the most consumed alcoholic beverages in the world, and their production generates enormous amounts of by-product materials. This ranges from spent grain, spent yeast, spent kieselguhr, trub, carbon dioxide, pot ale, and distilled gin spent botanicals. The present circular economy dynamics and increased awareness on resource use for enhanced sustainable production practices have driven changes and innovations in the management practices and utilization of these by-products. These include food product development, functional food applications, biotechnological applications, and bioactive compounds extraction. As a result, the brewing and distilling sector of the food and drinks industry is beginning to see a shift from conventional uses of by-products such as animal feed to more innovative applications. This review paper therefore explored some of these valorization initiatives and the current state of the art.

The Potential of Brewer’s Spent Grain in the Circular Bioeconomy: State of the Art and Future Perspectives

Brewer’s spent grain (BSG) accounts for approximately 85% of the total mass of solid by-products in the brewing industry and represents an important secondary raw material of future biorefineries. Currently, the main application of BSG is limited to the feed and food industry. There is a strong need to develop sustainable pretreatment and fractionation processes to obtain BSG hydrolysates that enable efficient biotransformation into biofuels, biomaterials, or biochemicals. This paper aims to provide a comprehensive insight into the availability of BSG, chemical properties, and current and potential applications juxtaposed with the existing and emerging markets of the pyramid of bio-based products in the context of sustainable and circular bioeconomy. An economic evaluation of BSG for the production of highly valuable products is presented in the context of sustainable and circular bioeconomy targeting the market of Central and Eastern European countries (BIOEAST region).

Fed-batch simultaneous saccharification and fermentation including in-situ recovery for enhanced butanol production from rice straw

This paper describes a study of fed-batch SSFR (simultaneous saccharification, fermentation and recovery) for butanol production from alkaline-pretreated rice straw (RS) in a 2-L stirred tank reactor. The initial solid (9.2% w/v) and enzyme (19.9 FPU g-dw^-1) loadings were previously optimized by 50-mL batch SSF assays. Maximum butanol concentration of 24.80 g L^-1 was obtained after three biomass feedings that doubled the RS load (18.4% w/v). Butanol productivity (0.344 g L^-1h^-1) also increased two-fold in comparison with batch SSF without recovery (0.170 g L^-1h^-1). Although fed-batch SSFR was able to operate with a single initial enzyme dosage, an extra dosage of nutrients was required with the biomass additions to achieve this high productivity. The study showed that SSFR can efficiently improve butanol production from a lignocellulosic biomass accompanied by the efficient use of the enzyme.

Ideal conditions of microwave-assisted acid pretreatment of sugarcane straw allow fermentative butyric acid production without detoxification step

Sugarcane straw (SCS) was pretreated with dilute sulfuric acid assisted by microwave to magnify fermentable sugars and to minimize the concentration of inhibitors in the hydrolysates. The optimum conditions for maximum recovery of sugars were 162 °C and 0.6% (w/v) H₂SO₄. The low level of inhibitors, such as acetate (2.9 g/L) and total phenolics (1.4 g/L), in the SCS slurry from the pretreatment stage allowed the enzymatic hydrolysis and fermentation steps to occur without detoxification. Besides consuming the total sugar content (31.0 g/L), Clostridium beijerinckii Br21 was able to use acetate from the SCS hydrolysate, to give butyric acid at high conversion factor (0.49 g of butyric acid /g of sugar). The optimized pretreatment conditions spared acid, time, and the detoxification stage, making bio-butyric acid production from SCS extremely attractive.

Production of butanol from distillers' grain waste by a new aerotolerant strain of Clostridium beijerinckii LY-5

A new aerotolerant strain of Clostridium beijerinckii LY-5 was isolated from the pit mud of the Chinese Baijiu-making process for butanol production. Plackett-Burman design and artificial neural network were used to optimize the fermentation medium and a total of 13.54 ± 0.22 g/L butanol and 19.91 ± 0.52 g/L ABE were attained under aerotolerant condition. Moreover, distillers' grain waste (DGW), the main by-product in the Baijiu production process, was utilized as potential substrate for butanol production. DGW was hydrolyzed by α-amylase and glucoamylase and then fermented after a detoxifying process of overliming. Butanol and ABE concentrations were 9.02 ± 0.18 and 9.57 ± 0.19 g/L with the yield of 0.21 and 0.23 g/g sugar, respectively. The higher ratio of butanol to ABE might be caused by the inhibitors in DGW medium affecting the metabolic pathways of C. beijerinckii LY-5 and approximately 1.48 ± 0.04 g/L isopropanol was found at the end of fermentation. This work highlights the feasibility of using DGW as a promising feedstock for butanol production by a new aerotolerant strain of C. beijerinckii LY-5, with benefit to the environment.

Recent advances in biotechnological valorization of brewers' spent grain

Brewers' spent grain (BSG) is the most abundant by-product of beer-brewing. BSG is rich in nutrients such as protein, fiber, minerals, and vitamins, and therefore it is conventionally used as low-cost animal feed. On the other hand, alternative utilization of BSG has gained increased attention during recent years due to technological progress in its processing and the emergence of the concept of circular economy. The valorization of BSG through biotechnological approaches is environmentally friendly and sustainable. This review was focused on recent advancements in the conversion of BSG into value-added products, including bioenergy (ethanol, butanol, hydrogen, biodiesel, and biogas), organic acids, enzymes, xylitol, oligosaccharides, and single cell protein, via biotechnological approaches. In addition, the potential applications of BSG as immobilization matrices in bioprocesses have been reviewed.

Feasibility Analysis of Brewers’ Spent Grain for Energy Use: Waste and Experimental Pellets

Waste production is increasing every day as a consequence of human activities; thus, its valorization is becoming more important. For this purpose, the usage of wastes as biofuels is one of the most important aspects of sustainable strategies. This is the case of the main waste generated in brewing industries: brewers’ spent grain (BSG). In this sector, microbreweries are not able to properly manage the wastes that they generate due to lack of space. Consequently, the transformation of BSG to a high-quality biofuel might be an interesting option for this kind of small industry. In this work, we carried out a physical-energy characterization of BSG, as well as pellets from this waste. The initial characterization showed slightly unfavorable results concerning N and ash, with values of 3.76% and 3.37% db, respectively. Nevertheless, the physical characterization of the pellets was very good, with acceptable bulk density (662.96 kg·m−3 wb) and low heating value (LHV; 17.65 MJ·kg−1 wb), among others. This situation is very favorable for any of the intended uses (for energy use or animal feed, among others).

Efficient biobutanol production by acetone-butanol-ethanol fermentation from spent coffee grounds with microwave assisted dilute sulfuric acid pretreatment

The integral valorization of potential sugars (cellulosic and hemicellulosic) from spent coffee grounds (SCG), a lignocellulosic residue, is proposed in this work. With this aim, the microwave assisted dilute sulfuric acid pretreatment has been optimized, leading to a hemicellulosic sugar recovery in the pretreatment liquid (HSR_L) and an enzymatic hydrolysis yield of 79 and 98%, respectively, at 160.47 °C and 1.5% H₂SO₄. Moreover, the complete digestibility of cellulose (enzymatic hydrolysis yield = 100%) was also discovered for non-pretreated SCG, which is very interesting. Secondly, the production of biobutanol, an advanced biofuel, is also proposed from pretreated SCG enzymatic hydrolysate and pretreatment liquid achieved under optimal conditions. These were fermented by Clostridium beijerinckii, yielding 95 kg butanol/t SCG (dry matter) and 151 kg acetone-butanol-ethanol/t SCG (dry matter).

The role of microorganisms on biotransformation of brewers' spent grain

Brewers' spent grain (BSG) is the most abundant by-product of brewing. Due to its microbiological instability and high perishability, fresh BSG is currently disposed of as low-cost cattle feed. However, BSG is an appealing source of nutrients to obtain products with high added value through microbial-based transformation. As such, BSG could become a potential source of income for the brewery itself. While recent studies have covered the relevance of BSG chemical composition in detail, this review aims to underline the importance of microorganisms from the stabilization/contamination of fresh BSG to its biotechnological exploitation. Indeed, the evaluation of BSG-associated microorganisms, which include yeast, fungi, and bacteria, can allow their safe use and the best methods for their exploitation. This bibliographical examination is particularly focused on the role of microorganisms in BSG exploitation to (1) produce enzymes and metabolites of industrial interest, (2) supplement human and animal diets, and (3) improve soil fertility. Emerging safety issues in the use of BSG as a food and feed additive is also considered, particularly considering the presence of mycotoxins.Key points• Microorganisms are used to enhance brewers' spent grain nutritional value.• Knowledge of brewers' spent grain microbiota allows the reduction of health risks. Graphical abstract.

By-Products in the Malting and Brewing Industries—Re-Usage Possibilities

Beer production includes the formation of different by-products such as wastewater, spent grains, spent hops, and yeast. In addition to these well-known by-products, it is necessary to mention germ/rootlets, which also remain after the malting process. Given that a huge amount of beer is produced annually worldwide, by-products are available in large quantities throughout the year. Spent grains, spent hops, and spent yeasts are high-energy raw materials that possess a great potential for application in the branch of biotechnology, and the food industry, but these by-products are commonly used as livestock feed, disposed of in the fields, or incinerated. Breweries by-products can be utilized for microalgae production, biofuel production, extraction of proteins, polyphenolic, antioxidative substances, etc. This paper aims to address each of these by-products with an emphasis on their possible application in biotechnology and other industries.

Minimalistic Cellulosome of the Butanologenic Bacterium Clostridium saccharoperbutylacetonicum

Clostridium saccharoperbutylacetonicum is a mesophilic, anaerobic, butanol-producing bacterium, originally isolated from soil. It was recently reported that C. saccharoperbutylacetonicum possesses multiple cellulosomal elements and would potentially form the smallest cellulosome known in nature. Its genome contains only eight dockerin-bearing enzymes, and its unique scaffoldin bears two cohesins (Cohs), three X2 modules, and two carbohydrate-binding modules (CBMs). In this study, all of the cellulosome-related modules were cloned, expressed, and purified. The recombinant cohesins, dockerins, and CBMs were tested for binding activity using enzyme-linked immunosorbent assay (ELISA)-based techniques. All the enzymes were tested for their comparative enzymatic activity on seven different cellulosic and hemicellulosic substrates, thus revealing four cellulases, a xylanase, a mannanase, a xyloglucanase, and a lichenase. All dockerin-containing enzymes interacted similarly with the second cohesin (Coh2) module, whereas Coh1 was more restricted in its interaction pattern. In addition, the polysaccharide-binding properties of the CBMs within the scaffoldin were examined by two complementary assays, affinity electrophoresis and affinity pulldown. The scaffoldin of C. saccharoperbutylacetonicum exhibited high affinity for cellulosic and hemicellulosic substrates, specifically to microcrystalline cellulose and xyloglucan. Evidence that supports substrate-dependent in vivo secretion of cellulosomes is presented. The results of our analyses contribute to a better understanding of simple cellulosome systems by identifying the key players in this minimalistic system and the binding pattern of its cohesin-dockerin interaction. The knowledge gained by our study will assist further exploration of similar minimalistic cellulosomes and will contribute to the significance of specific sets of defined cellulosomal enzymes in the degradation of cellulosic biomass.IMPORTANCE Cellulosome-producing bacteria are considered among the most important bacteria in both mesophilic and thermophilic environments, owing to their capacity to deconstruct recalcitrant plant-derived polysaccharides (and notably cellulose) into soluble saccharides for subsequent processing. In many ecosystems, the cellulosome-producing bacteria are particularly effective "first responders." The massive amounts of sugars produced are potentially amenable in industrial settings to further fermentation by appropriate microbes to biofuels, notably ethanol and butanol. Among the solvent-producing bacteria, Clostridium saccharoperbutylacetonicum has the smallest cellulosome system known thus far. The importance of investigating the building blocks of such a small, multifunctional nanomachine is crucial to understanding the fundamental activities of this efficient enzymatic complex.

An evaluation of sonication pretreatment for enhancing saccharification of brewers' spent grain

This paper deals with the investigation of ultrasound (US) pretreatment of brewer's spent grain (BSG) as a means of releasing fermentable sugars, and the subsequent production of ethanol from this lignocellulosic biomass. Using response surface methodology (RSM), the influence of US power, time, temperature and biomass loading on fermentable sugar yield from BSG was studied. The optimal conditions were found to be 20% US power, 60 min, 26.3 °C, and 17.3% w/v of biomass in water. Under these conditions, an approximate 2.1-fold increase in reducing sugar yield (325 ± 6 mg/g of biomass) was achieved, relative to untreated BSG (151.1 ± 10 mg/g of biomass). In contrast to acid or alkaline pretreatment approaches, the use of water obviated the need for neutralization for the recovery of sugars. The characterization of native and pretreated BSG was performed by HPLC, FTIR, SEM and DSC. Fermentation studies using S. cerevisiae growing on pretreated BSG resulted in a conversion of 66% of the total sugar content ininto ethanol with an ethanol content of 17.73 ± 2 g/ 100 g of pretreated BSG. These results suggest that ultrasound pretreatment is a promising technology for increased valorization of BSG as a feedstock for production of bioethanol, and points ton the need for further work in this area.

Feasibility of using biochar as buffer and mineral nutrients replacement for acetone-butanol-ethanol production from non-detoxified switchgrass hydrolysate

Biochar can be an inexpensive pH buffer and source of mineral and trace metal nutrients in acetone-butanol-ethanol (ABE) fermentation. This study evaluated the feasibility of replacing expensive 4-morpholineethanesulfonic acid (MES) P2 buffer and mineral nutrients with biochar made from switchgrass (SGBC), forage sorghum (FSBC), redcedar (RCBC) and poultry litter (PLBC) for ABE fermentation. Fermentations using Clostridium beijerinckii ATCC 51743 in glucose and non-detoxified switchgrass hydrolysate media were performed at 35 °C in 250 mL bottles for 72 h. Medium containing buffer and minerals without biochar was the control. Similar ABE production (about 18.0 g/L) in glucose media with SGBC, FSBC and RCBC and control was measured. However in non-detoxified switchgrass hydrolysate medium, SGBC, RCBC and PLBC produced more ABE (about 18.5 g/L) than the control (10.1 g/L). This demonstrates that biochar is an effective buffer and mineral supplement for ABE production from lignocellulosic biomass without costly detoxification process.

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

BACKGROUND

The 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.

RESULTS

SE 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.

CONCLUSIONS

SE 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.

Butanol production from laccase-pretreated brewer's spent grain

BACKGROUND

Beer is the most popular alcoholic beverage worldwide. In the manufacture of beer, various by-products and residues are generated, and the most abundant (85% of total by-products) are spent grains. Thanks to its high (hemi)cellulose content (about 50% w/w dry weight), this secondary raw material is attractive for the production of second-generation biofuels as butanol through fermentation processes.

RESULTS

This study reports the ability of two laccase preparations from Pleurotus ostreatus to delignify and detoxify milled brewer's spent grains (BSG). Up to 94% of phenols reduction was achieved. Moreover, thanks to the mild conditions of enzymatic pretreatment, the formation of other inhibitory compounds was avoided allowing to apply the sequential enzymatic pretreatment and hydrolysis process (no filtration and washing steps between the two phases). As expected, the high detoxification and delignification yields achieved by laccase pretreatment resulted in great saccharification. As a fact, no loss of carbohydrates was observed thanks to the novel sequential strategy, and thus the totality of polysaccharides was hydrolysed into fermentable sugars. The enzymatic hydrolysate was fermented to acetone-butanol-ethanol (ABE) by Clostridium acetobutilycum obtaining about 12.6 g/L ABE and 7.83 g/L butanol within 190 h.

CONCLUSIONS

The applied sequential pretreatment and hydrolysis process resulted to be very effective for the milled BSG, allowing reduction of inhibitory compounds and lignin content with a consequent efficient saccharification. C. acetobutilycum was able to ferment the BSG hydrolysate with ABE yields similar to those obtained by using synthetic media. The proposed strategy reduces the amount of wastewater and the cost of the overall process. Based on the reported results, the potential production of butanol from the fermentation of BSG hydrolysate can be envisaged.

Combining chemical flocculation and bacterial co-culture of Cupriavidus taiwanensis and Ureibacillus thermosphaericus to detoxify a hardwood hemicelluloses hydrolysate and enable acetone-butanol-ethanol fermentation leading to butanol

Butanol, a fuel with better characteristics than ethanol, can be produced via acetone-butanol-ethanol (ABE) fermentation using lignocellulosic biomass as a carbon source. However, many inhibitors present in the hydrolysate limit the yield of the fermentation process. In this work, a detoxification technology combining flocculation and biodetoxification within a bacterial co-culture composed of Ureibacillus thermosphaericus and Cupriavidus taiwanensis is presented for the first time. Co-culture-based strategies to detoxify filtered and unfiltered hydrolysates have been investigated. The best results of detoxification were obtained for a two-step approach combining flocculation to biodetoxification. This sequential process led to a final phenolic compounds concentration of 1.4 g/L, a value close to the minimum inhibitory level observed for flocculated hydrolysate (1.1 g/L). The generated hydrolysate was then fermented with Clostridium acetobutylicum ATCC 824 for 120 h. A final butanol production of 8 g/L was obtained, although the detoxified hydrolysate was diluted to reach 0.3 g/L of phenolics to ensure noninhibitory conditions. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2753, 2019.

Pretreatment and hydrolysis of lignocellulosic wastes for butanol production: Challenges and perspectives

Butanol is acknowledged as a drop-in biofuel that can be used in the existing transportation infrastructure, addressing the needs for sustainable liquid fuel. However, before becoming a thoughtful alternative for fossil fuel, butanol should be produced efficiently from a widely-available, renewable, and cost-effective source. In this regard, lignocellulosic materials, the main component of organic wastes from agriculture, forestry, municipalities, and even industries seems to be the most promising source. The butanol-producing bacteria, i.e., Clostridia sp., can uptake a wide range of hexoses, pentoses, and oligomers obtained from hydrolysis of cellulose and hemicellulose content of lignocelluloses. The present work is dedicated to reviewing different processes containing pretreatment and hydrolysis of hemicellulose and cellulose developed for preparing fermentable hydrolysates for biobutanol production.