Recovery of sugars and amino acids from brewers' spent grains using subcritical water hydrolysis in a single and two sequential semi-continuous flow-through reactors.

This study evaluated the subcritical water hydrolysis (SWH) of brewer's spent grains (BSG) to obtain sugars and amino acids. The experimental conditions investigated the hydrolysis of BSG in a single flow-through reactor and in two sequential reactors operated in semi-continuous mode. The hydrolysis experiments were carried out for 120 min at 15 MPa, 5 mL water min-1, at different temperatures (80 - 180 °C) and using an S/F of 20 and 10 g solvent g-1 BSG, for the single and two sequential reactors, respectively. The highest monosaccharide yields were obtained at 180 °C in a single reactor (47.76 mg g-1 carbohydrates). With these operational conditions, the hydrolysate presented xylose (0.477 mg mL-1) and arabinose (1.039 mg mL-1) as main sugars, while low contents of furfural (310.7 µg mL-1), 5-hydroxymethylfurfural (<1 mg L-1), and organic acids (0.343 mg mL-1) were obtained. The yield of proteins at 180 °C in a process with a single reactor was 43.62 mg amino acids g-1 proteins, where tryptophan (215.55 µg mL-1), aspartic acid (123.35 µg mL-1), valine (64.35 µg mL-1), lysine (16.55 µg mL-1), and glycine (16.1 µg mL-1) were the main amino acids recovered in the hydrolysate. In conclusion, SWH pretreatment is a promising technology to recover bio-based compounds from BSG; however, further studies are still needed to increase the yield of bioproducts from lignocellulosic biomass to explore two sequential reactors.

Recent progress in the microbial production of xylonic acid.

Interest in the production of renewable chemicals from biomass has increased in the past years. Among these chemicals, carboxylic acids represent a significant part of the most desirable bio-based products. Xylonic acid is a five-carbon sugar-acid obtained from xylose oxidation that can be used in several industrial applications, including food, pharmaceutical, and construction industries. So far, the production of xylonic acid has not yet been available at an industrial scale; however, several microbial bio-based production processes are under development. This review summarizes the recent advances in pathway characterization, genetic engineering, and fermentative strategies to improve xylonic acid production by microorganisms from xylose or lignocellulosic hydrolysates. In addition, the strengths of the available microbial strains and processes and the major requirements for achieving biotechnological production of xylonic acid at a commercial scale are discussed. Efficient native and engineered microbial strains have been reported. Xylonic acid titers as high as 586 and 171 g L-1 were obtained from bacterial and yeast strains, respectively, in a laboratory medium. Furthermore, relevant academic and industrial players associated with xylonic acid production will be presented.

Heterologous Expression of Lignocellulose-Modifying Enzymes in Microorganisms: Current Status.

Heterologous expression of the carbohydrate-active enzymes in microorganisms is a promising approach to produce bio-based compounds, such as fuels, nutraceuticals and other value-added products from sustainable lignocellulosic sources. Several microorganisms, including Saccharomyces cerevisiae, Escherichia coli, and the filamentous fungi Aspergillus nidulans, have unique characteristics desirable for a biorefinery production approach like well-known genetic tools, thermotolerance, high fermentative capacity and product tolerance, and high amount of recombinant enzyme secretion. These microbial factories are already stablished in the heterologous production of the carbohydrate-active enzymes to produce, among others, ethanol, xylooligosaccharides and the valuable coniferol. A complete biocatalyst able to heterologous express the CAZymes of glycoside hydrolases, carbohydrate esterases and auxiliary activities families could release these compounds faster, with higher yield and specificity. Recent advances in the synthetic biology tools could expand the number and diversity of enzymes integrated in these microorganisms, and also modify those already integrated. This review outlines the heterologous expression of carbohydrate-active enzymes in microorganisms, as well as recent updates in synthetic biology.

Isolation of xylose-assimilating yeasts and optimization of xylitol production by a new Meyerozyma guilliermondii strain.

Production of xylitol from lignocellulosic biomass is of interest to modern biorefineries, because this biomass should be processed into a spectrum of chemicals (bio-based products) and not only energy. The isolation of new yeast strains capable of efficiently converting xylose into xylitol and withstanding inhibitors released from biomass hydrolysis can contribute to making its production feasible in biorefineries. Forty-three out of 128 yeast strains isolated from the gut of Passalidae beetles were capable of assimilating xylose as the sole carbon source. Meyerozyma guilliermondii UFV-1 was selected due to its ability to grow and ferment D-xylose in a synthetic medium. This yeast assimilated the broad range of sugars present in lignocellulosic biomass hydrolysates, such as xylose, raffinose, cellobiose, rhamnose, arabinose, and glucose. Its optimum growth conditions were pH 8.0 and a temperature of 30 °C. In concentrations of 0.07 mol/L acetic acid, 0.05 mol/L 5-hydroximethylfurfural, and 0.04 mol/L furfural, M. guilliermondii UFV-1 did not grow. Maximum xylitol production in aerobiosis and hypoxia were 51.88 and 27.73 g/L, respectively. Under aerobic condition, xylose concentration and agitation rate were the factors which were statistically significant, while only the agitation rate was significant in hypoxia. We fitted a response surface (RS) that estimated the best agitation rate (113.33 rpm) and xylose concentration (90 g/L) for maximum xylitol production in aerobiosis. Therefore, M. guilliermondii UFV-1 displays potential for being used for xylitol production in biorefineries.

Fungal biodiversity to biotechnology.

Fungal habitats include soil, water, and extreme environments. With around 100,000 fungus species already described, it is estimated that 5.1 million fungus species exist on our planet, making fungi one of the largest and most diverse kingdoms of eukaryotes. Fungi show remarkable metabolic features due to a sophisticated genomic network and are important for the production of biotechnological compounds that greatly impact our society in many ways. In this review, we present the current state of knowledge on fungal biodiversity, with special emphasis on filamentous fungi and the most recent discoveries in the field of identification and production of biotechnological compounds. More than 250 fungus species have been studied to produce these biotechnological compounds. This review focuses on three of the branches generally accepted in biotechnological applications, which have been identified by a color code: red, green, and white for pharmaceutical, agricultural, and industrial biotechnology, respectively. We also discuss future prospects for the use of filamentous fungi in biotechnology application.