One-pot production of lactic acid from rice straw pretreated with ionic liquid

Application of microbial resources in biorefineries: Current trend and future prospects

The recent growing interest in sustainable and alternative sources of energy and bio-based products has driven the paradigm shift to an integrated model termed "biorefinery." Biorefinery framework implements the concepts of novel eco-technologies and eco-efficient processes for the sustainable production of energy and value-added biomolecules. The utilization of microbial resources for the production of various value-added products has been documented in the literatures. However, the appointment of these microbial resources in integrated resource management requires a better understanding of their status. The main of aim of this review is to provide an overview on the defined positioning and overall contribution of the microbial resources, i.e., algae, fungi and bacteria, for various bioprocesses and generation of multiple products from a single biorefinery. By utilizing waste material as a feedstock, biofuels can be generated by microalgae while sequestering environmental carbon and producing value added compounds as by-products. In parallel, fungal biorefineries are prolific producers of lignocellulose degrading enzymes along with pharmaceutically important novel products. Conversely, bacterial biorefineries emerge as a preferred platform for the transformation of standard cells into proficient bio-factories, developing chassis and turbo cells for enhanced target compound production. This comprehensive review is poised to offer an intricate exploration of the current trends, obstacles, and prospective pathways of microbial biorefineries, for the development of future biorefineries.

Lactic Acid Production by Lactiplantibacillus plantarum AC 11S-Kinetics and Modeling

Lactic acid is a versatile chemical with wide application in many industries. It can be produced by the fermentation of different sugars by various lactobacilli and investigations on lactic acid production from different substrates and by different strains are still in progress. The present study aimed to study lactic acid production from lactose by Lactiplantibacillus plantarum AC 11S and to choose a mathematical model describing in the best way the experimental data obtained. The influence of initial substrate concentration was investigated, and optimal pH and temperature were determined. An unstructured mathematical model was developed comprising equations for bacterial growth, substrate consumption, and product formation. The model was solved with different terms for specific growth rates considering substrate and/or product inhibition. The best bacterial growth and lactic acid production were achieved at pH = 6.5 and 30 °C. Production of lactic acid was mainly growth-associated, and at initial substrate concentration over 15 g/L, a considerable product inhibition was observed. The parameters of different models were determined and compared. The modified Gompertz equation gave the best fit when solving only the equation for biomass growth at different initial substrate concentrations. Solving the entire set of differential equations for bacterial growth, substrate consumption, and product formation, the best results were obtained when using a variant of the logistic equation for biomass growth. This variant included a term for product inhibition and described in the best way all experimental data. Solving the model for different biomass concentrations showed that an increase in biomass led to a shorter lag phase and the stationary phase was reached faster. The results obtained, optimum conditions and the kinetic model, are good bases for studying pH-controlled fermentation, as well as a continuous process.

High titer (>200 g/L) lactic acid production from undetoxified pretreated corn stover

Lignocellulosic biomass is a reliable feedstock for lactic acid fermentation, low product titers hamper the scale production of cellulosic lactic acid. In this study, a Densifying Lignocellulosic biomass with Chemicals (sulfuric acid) pretreatment based cellulosic lactic acid biorefinery system was developed and demonstrated from multi-dimensions of producing bacteria, fermentation modes, corn stover solid loadings, fermentation vessels, and product purification. Results suggested that several lactic acid bacteria exhibited high fermentation activity in high solid loading corn stover hydrolysates. Remarkably, simultaneous saccharification co-fermentation performed in 100-mL flasks enabled 210.1 g/L lactic acid from 40% solid loading corn stover hydrolysate. When simultaneous saccharification co-fermentation was performed in 3-L bioreactors, 157.4 g/L lactic acid was obtained from 35% solid loading corn stover hydrolysate. These obtained lactic acid titers are the highest reports until now when lignocellulosic biomasses are used as substrates, making it efficient for scale production of cellulosic lactic acid.

Integrated fermentative production and downstream processing of L-malic acid by Aspergillus wentii using cassava peel waste

L-malic acid (L-MA) is an industrially significant chemical with enormous potential. The fungal cell factories could be exploited to harvest it on large scales. In our study, Aspergillus wentii strain (MTCC 1901 ^T) was explored for L-MA production. Initially, the L-MA production was carried out using glucose with optimization of parameters influencing product accumulation (pH and CaCO₃). The fermentation resulted in L-MA titer of 37.9 g/L with 0.39 g/g yield. Then, cassava peel waste (CPW) was used for L-MA production by separate hydrolysis and fermentation. Optimized acidic and enzymatic hydrolysis resulted in glucose release of 0.53 and 0.66 g/g CPW, respectively. The strain accumulated 20.9 g/L and 33.1 g/L L-MA with corresponding yields of 0.25 g/g and 0.34 g/g during batch cultivation using acid and enzyme hydrolysate, respectively. Finally, the produced L-MA was separated using an inexpensive solvent extraction method. Among various solvents used, n-butanol exhibited maximum L-MA extraction efficiency (31%).

Efficient production of acetoin from lactate by engineered Escherichia coli whole-cell biocatalyst

Acetoin, an important and high-value added bio-based platform chemical, has been widely applied in fields of foods, cosmetics, chemical synthesis, and agriculture. Lactate is a significant intermediate short-chain carboxylate in the anaerobic breakdown of carbohydrates that comprise ~ 18% and ~ 70% in municipal wastewaters and some food processing wastewaters, respectively. In this work, a series of engineered Escherichia coli strains were constructed for efficient production of acetoin from cheaper and abundant lactate through heterogenous co-expression of fusion protein (α-acetolactate synthetase and α-acetolactate decarboxylase), lactate dehydrogenase and NADH oxidase, and blocking acetate synthesis pathways. After optimization of whole-cell bioconversion conditions, the engineered strain BL-11 produced 251.97 mM (22.20 g/L) acetoin with a yield of 0.434 mol/mol in shake flasks. Moreover, a titer of 648.97mM (57.18 g/L) acetoin was obtained in 30 h with a yield of 0.484 mol/mol lactic acid in a 1-L bioreactor. To the best of our knowledge, this is the first report on the production of acetoin from renewable lactate through whole-cell bioconversion with both high titer and yield, which demonstrates the economy and efficiency of acetoin production from lactate. Key Points • The lactate dehydrogenases from different organisms were expressed, purified, and assayed. • It is the first time that acetoin was produced from lactate by whole-cell biocatalysis. • The highest titer of 57.18 g/L acetoin was obtained with high theoretical yield in a 1-L bioreactor.

The transformations of cellulose after concentrated sulfuric acid treatment and its impact on the enzymatic saccharification

BACKGROUND

The dense structure of cellulose lowers its reactivity and hinders its applications. Concentrated sulfuric acid is an ideal solvent to dissolve cellulose and thus has been used widely to treat cellulose. However, the changes of cellulose after reaction with concentrated sulfuric acid at near-limit S/L ratio and its effect on enzymatic saccharification still need further investigation.

RESULTS

In this study, the interactions between cellulose (Avicel) and 72% sulfuric acid at very low acid loading conditions of 1:2 to 1:3 (S/L ratio) were studied for the enhanced production of glucose. The Avicel gradually transformed from cellulose I structure to cellulose II structure during the sulfuric acid treatment. Other physicochemical characteristics of Avicel also changed dramatically, such as the degree of polymerization, particle size, crystallinity index, and surface morphology. After acid treatment, both the yield and productivity of glucose from cellulose increased significantly under a very low enzyme loading of 5 FPU/g-cellulose. The glucose yields for raw cellulose and acid-treated (30 min) were 57% and 85%, respectively.

CONCLUSION

Low loadings of concentrated sulfuric acid were proven to be effective to break the recalcitrance of cellulose for enzymatic saccharification. A positive correlation between cellulose CrI and glucose yield was found for concentrated sulfuric acid-treated cellulose, which was opposite to previous reports. Cellulose II content was found to be an important factor that affects the conversion of cellulose to glucose.

Microbial production of lactic acid using organic wastes as low-cost substrates

Lactic acid is a natural organic acid with diverse of applications in food, pharmaceutical, cosmetics, and chemical industry. Recently, the demand of lactic acid has been grown due to its utilization for polylactic acid production. Microbial production of lactic acid production is preferable due to optical purity of product, utilization of low cost substrates, and low energy requirement. Lignocellulosic biomass and other organic wastes are considered potential raw materials for cost-effective production of lactic acid. The raw materials are either hydrolyzed by enzymes or dilute acids to release the reducing sugars that are fermented in to lactic acid. This review has been focussed on microbial production of lactic acid using different organic wastes as low cost substrate.

One-pot d-lactic acid production using undetoxified acid-pretreated corncob slurry by an adapted Pediococcus acidilactici

Inhibitor tolerance is still a bottleneck for lactic acid bacteria in lignocellulose biorefinery, while it is hard to obtain one engineered strain with strong tolerance to all inhibitors. Herein, a robust adapted d-lactic acid producing strain Pediococcus acidilactici XH11 was obtained by 111 days' long-term adaptive evolution in undetoxified corncob prehydrolysates. The adapted strain had higher inhibitors tolerance compared to the parental strain, primarily due to its increased conversion capacities of four typical aldehyde inhibitors (furfural, HMF, vanillin, and 4-hydroxybenzaldehyde). One-pot simultaneous saccharification and co-fermentation was successfully achieved using the whole slurry of acid-pretreated corncob without solid-liquid separation and detoxification, by applying the adapted P. acidilactici XH11. Finally, 61.9 g/L of d-lactic acid was generated after 96 h' fermentation (xylose conversion of 89.9 %) with the overall yield of 0.48 g/g dry corncob. This study gave an important option for screening of industrial strains in cellulosic lactic acid production processes.

Pretreatment of Jerusalem artichoke stalk using hydroxylammonium ionic liquids and their influences on 2,3-butanediol fermentation by Bacillus subtilis

Pretreatment of lignocellulose is a vital step for biological production of bio-chemicals and bio-fuels. In this work, the pretreatment of Jerusalem artichoke stalk (JAS) by hydroxylammonium ionic liquids was evaluated based on pretreatment efficiency including polysaccharide recovery and enzymatic digestibility, and influence of ionic liquids on 2,3-butanediol fermentation using Bacillus subtilis. The results showed ethanolammonium acetate (EOAA) was efficient in JAS pretreatment, and maximum cell density was increased 25% when EOAA concentration was not greater than 0.3 mol/L in medium, while the total concentration of acetoin and 2,3-butanediol was 15% greater than the control at 0.1 mol/L EOAA. After the pretreatment under optimized conditions of 170 °C for 5-h and liquid-solid ratio of 18, about 87% cellulose and 75% hemicellulose were recovered, and glucose yield of 64% and xylose of 66% were obtained after 24-h hydrolysis of JAS residue by cellulase (15 FPU/g) with solid loading of 10 wt%.

An innovative approach for reducing the water and alkali consumption in the lactic acid fermentation via the reuse of pretreated liquid

This study focuses on enhancing lactic acid (LA) production and declining water and alkali consumption by reusing the pretreated liquid (PL) of spent mushroom substance (SMS) in the co-fermentation of food waste (FW) and SMS. First, the compositions of PL are identified, and the effects of the PL inhibitors on enzymatic hydrolysis and fermentation are explored. The PL phenol concentrations exceeded 2 g/L, which affected LA fermentation. Therefore, PL phenols were removed by adjusting the pH value, and the detoxified PL (DPL) phenol concentrations were 70.3% lower than those of PL. Different PL:DPL ratios were established to reuse in the fermentation process, and the LA concentration in the 50% PL + 50% DPL group was the highest (56.7 g/L). Then, pretreated SMS was not water-washed, and a neutralizer was prepared with the PL, LA production remained unchanged. Water and NaOH consumption decreased by 84.6% and 52.0%, respectively, and no wastewater was produced.

Fermentative Lactic Acid Production From Lignocellulosic Feedstocks: From Source to Purified Product

The second (lignocellulosic biomass and industrial wastes) and third (algal biomass) generation feedstocks gained substantial interest as a source of various value-added chemicals, produced by fermentation. Lactic acid is a valuable platform chemical with both traditional and newer applications in many industries. The successful fractionation, separation, and hydrolysis of lignocellulosic biomass result in sugars’ rich raw material for lactic acid fermentation. This review paper aims to summarize the investigations and progress in the last 5 years in lactic acid production from inexpensive and renewable resources. Different aspects are discussed—the type of raw materials, pretreatment and detoxification methods, lactic acid-producers (bacteria, fungi, and yeasts), use of genetically manipulated microorganisms, separation techniques, different approaches of process organization, as well as main challenges, and possible solutions for process optimization.

Valorization of municipal organic waste into purified lactic acid

Municipal organic waste (biowaste) consists of food derived starch, protein and sugars, and lignocellulose derived cellulose, hemicellulose, lignin and pectin. Proper management enables nutrient recycling and sustainable production of platform chemicals such as lactic acid (LA). This review gathers the most important information regarding use of biowaste for LA fermentation covering pre-treatment, enzymatic hydrolysis, fermentation and downstream processing to achieve high purity LA. The optimal approach was found to treat the two biowaste fractions separately due to different pre-treatment and enzyme needs for achieving enzymatic hydrolysis and to do continues fermentation to achieve high cell density and high LA productivity up to 12 g/L/h for production of both L and D isomers. The specific productivity was 0.4 to 0.5 h^-1 but with recalcitrant biomass, the enzymatic hydrolysis was rate limiting. Novel purification approaches included reactive distillation and emulsion liquid membrane separation yielding purities sufficient for polylactic acid production.

Direct production of 2, 5-Furandicarboxylicacid from raw biomass by manganese dioxide catalysis cooperated with ultrasonic-assisted diluted acid pretreatment

In recent years, 2, 5-furandicarboxylic acid (FDCA) has attracted much attention as the precursor of bio-polyester materials. A coupled process of ultrasonic-assisted dilute acid pretreatment and MnO₂ was designed in this study to directly produce FDCA from lignocellulosic biomass, which is different from the traditional preparation process. Moreover, the critical parameters in the process were analyzed and optimized by the response surface method. The yield of FDCA could reach 52.1% under the optimal conditions. The reaction mechanism indicated that heavy metal elements in lignocellulosic biomass could play the role of the Lewis acid catalyst to promote the formation of FDCA to a certain extent. With the increase of temperature, the heavy metals transfer in biomass from the solid phase to the liquid phase increased, but most of them remain in the former. Therefore, further purification and treatment measures are worthy of attention.