Glycosaminoglycans (GAGs) are a class of linear polysaccharides, consisting of alternating disaccharide sequences of uronic acid and hexosamines (or galactose) with and without sulfation. They can interact with various proteins, such as growth factors, receptors and cell adhesion molecules, endowing these with various biological and pharmacological activities. Such activities make GAGs useful in health care products and medicines. Currently, all GAGs, with the exception of hyaluronan, are produced by extraction from animal tissues. However, limited availability, poor control of animal tissues, impurities, viruses, prions, endotoxins, contamination and other problems have increased the interest in new approaches for GAG production. These new approaches include GAGs production by chemical synthesis, chemoenzymatic synthesis and metabolic engineering. One chemically synthesized heparin pentasaccharide, fondaparinux sodium, is in clinical use. Mostly, hyaluronan today is prepared by microbial fermentation, largely replacing hyaluronan from rooster comb. The recent gram scale chemoenzymatic synthesis of a heparin dodecasaccharide suggests its potential to replace currently used animal-sourced low molecular weight heparin (LMWH). Despite these considerable successes, such high-tech approaches still cannot meet worldwide demands for GAGs. This review gives a brief introduction on the manufacturing of unfractionated and low molecular weight heparins, the chemical synthesis and chemoenzymatic synthesis of GAGs and focuses on the progress in the bioengineered preparation of GAGs, particularly heparin.
Algal biomass has significant advantages over terrestrial plants in terms of CO2 sequestration, biomass productivity, wastewater treatment along with multiple biobased products synthesis. Metabolic versatility and high carbohydrate content of microalgal biomass act as a potential alternative feedstock to fossil resources and contribute towards the biobased economy growth. Effective biomass utilization would play a key role to establish sustainable bioprocess development and technology translation to the industrial community. In this framework, the present review discusses the renewable resource potential of algal biomass and its complete utilization for multiple biobased products synthesis in a closed-loop biorefinery approach. Various methods are discussed to obtain high biomass growth and pretreatments to obtain the maximum sugars solubilization. Further, combined bioprocesses were discussed for the production of biohydrogen, biomethane, bioethanol, short-chain fatty acids (SCFA), medium-chain fatty acids (MCFA), and biopolymers in a closed-loop approach.
It has now passed more than forty years since solid-state fermentation (SSF) research developments have gained importance for the scientific community. After so many years, numerous processes and equipment for SSF were studied and designed focusing on the production of different commercially relevant bioproducts such as enzymes, fermented food, such as Chinese daqu and koji, organic acids, pigments, phenolic compounds, aromas, biosorbents and so many others. However, no review paper has been focused yet specifically on agricultural and animal feed bioproducts obtained through SSF techniques. This review comprises the description of agricultural sub-products that have been employed in most important developed processes concerning the production of animal feed products and agricultural products such as spores, probiotics, biofungicides, bioinsecticides and other biopesticides, biofertilizers and plant growth hormones. Major designed SSF bioreactors are also described and the most important related cases of successful employment of the technique are reported. Finally, a summary of patents and innovations regarding SSF products and processes in this area is presented, showing that the main involved countries are China, South Korea, India and the USA. It is clear that the interest in this theme is increasing and that scientific and technological developments are still needed.
Lignin fractionation and depolymerization generates heterogeneous streams of aromatic compounds and conversion of aromatic compounds into valuable products, but it is not efficient. Many microbes in nature have evolved metabolic pathways to convert complex lignin polymers into aromatic compounds and transform these aromatic compounds into central intermediates for bioproduct synthesis. The objective of this paper is to review the recent process development of lignin bioconversion into aromatic compounds and bioproducts. Lignin structural and molecular changes during fractionation and depolymerization are presented. Subsequent lignin conversion into aromatic compounds by upper pathways and further converted into central metabolites and bioproducts via lower pathways are emphasized. In particular, enzymes and mediator systems to enhance lignin conversion and key intermediates in lignin catabolic pathways are discussed. Strategies to enhance bioproduct formation through lignin valorization are summarized.
Premature yeast flocculation (PYF) during beer fermentation is an undesired event by which yeast flocculate too early and heavily before the wort nutrition is exhausted. While PYF can be a major financial detriment to brewers, the conditions that trigger it and the chemical composition of PYF are poorly understood. Gas chromatography–mass spectrometry results from this study indicated that purified malt PYF factor consisted of numerous polysaccharides; however, no protein was identified. High concentrations of PYF promoted further yeast flocculation, which in turn decreased the rate of fermentation and increased acetaldehyde content of the beer. PYF factors were found to be derived primarily from malt husks and factors such as microbial content of the water used for germination, mixing malts with different PYF values, and presence of tannic acid were all found to influence the rate of yeast flocculation. Findings from this study may be beneficial in developing PYF prevention and control measures that can be applied to future brewing strategies.
Sulfuric acid was used in the pretreatment of corn stover to obtain xylose as a value-added by-product, and the pretreated corn stover (Pre-CS) was hydrolyzed to produce glucose for butanol fermentation. The aim of this work is to achieve high xylose accumulation and reduced wastewater by recycling the pretreatment solution. The pretreatment conditions were optimized as follows: 180 °C, 15 min, 1:7 solid–liquid ratio (w/w), 0.6% H2SO4 (w/w, first batch)/0.9% H2SO4 (w/w, second and third batches), in which pretreatment solution was recycled for three times. Under above conditions, pretreatment solution containing 56.3 g/L xylose and 4.5 g/L glucose was obtained. Pre-CS residue was further hydrolyzed by cellulase to achieve 35.7–39.9 g/L glucose. The condensed corn stover hydrolysate was subjected to simultaneous detoxification and sterilization using 1% (w/w) activated carbon and then applied in butanol fermentation. The highest butanol titer of 9.5 g/L was obtained in 72 h. The results provide a practical approach for coproducing xylose and biobutanol from corn stover.
Extracellular polymeric substances (EPS) are eco-friendly and economical biopolymers with a significant role in pollutant removal, bio-flocculation, settling and dewatering of activated sludge. In this study, growth profile and EPS production by an EPS-producing microbial strain (isolated from wastewater sludge or WWS) was studied using activated sludge fortified with glycerol. The study compared three crude glycerol samples as carbon sources from different biodiesel companies (BIO-LIQ, BIOCARDEL, ROTHSAY) and their effect on EPS production and characterisation was observed. The maximum slime EPS (S-EPS) concentration (12.34 g/L) was produced when sludge fortified with BIO-LIQ crude glycerol was used, higher than pure glycerol (10 g/L) at 72 h. The S-EPS was enhanced (16 g/L) when purified BIO-LIQ glycerol (by acid treatment) was used. It was also observed that S-EPS concentration increased 1.6–2.6 times by using sludge fortified with glycerol as compared to only glycerol (no sludge) as EPS production medium. In addition, the S-EPS produced from different glycerol samples yielded different characteristics in terms of protein-carbohydrate content, flocculation activity and dewaterability. The S-EPS from purified BIO-LIQ glycerol (with sludge) gave maximum flocculation activity and dewaterability i.e. 93.71% and 60.2% respectively. The comparison between Ca(OH)2 and NaOH used as alkaline sludge pre-treatment methods revealed that the EPS produced from Ca(OH)2-treated sludge fortified with glycerol solutions to be better in terms of protein content, flocculation activity and dewaterability. Structural composition analysis using Fourier Transform Infrared Spectroscopy (FT-IR) revealed the presence of distinct functional groups (carboxyl, hydroxyl, amine groups) in the produced S-EPS.
Tetramethylpyrazine (TTMP), an important aroma compound, was produced by Bacillus amyloliquefaciens XJB-104 with distillers’ grains as raw material. The yield of TTMP under optimized fermentation procedure was 3176.52 mg/L. TTMP in the fermentation broth was purified and the purity (> 99%) was measured by gas chromatography–mass spectrometry. Furthermore, the hepatoprotective activity of TTMP in ethanol–water system was evaluated by biochemical indicators of liver injury, parameters of antioxidant defense system and inflammatory response, and liver histopathological assessment in mice. Ethanol treatment increased serum levels of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase and lactate dehydrogenase, suggesting liver damage. Both high and low dose of TTMP significantly decreased levels of these indicators. Furthermore, the reduction in the activities or concentrations of superoxide dismutase, catalase, reduced glutathione and malondialdehyde in liver tissue caused by ethanol was significantly alleviated by TTMP. Increased inflammatory cytokines including transcription factor, tumor necrosis factor, interleukin-1beta, interleukin, macrophage chemoattractant protein, inducible nitric oxide synthase and cyclooxygenase were also suppressed by TTMP treatment. It is concluded that TTMP in ethanol–water system has potential liver-protective activity, especially when ethanol is consumed at low doses for short periods of time.