Aqueous two-phase extraction in bioseparations: an assessment

Systems level roadmap for solvent recovery and reuse in industries

Recovering waste solvent for reuse presents an excellent alternative to improving the greenness of industrial processes. Implementing solvent recovery practices in the chemical industry is necessary, given the increasing focus on sustainability to promote a circular economy. However, the systematic design of recovery processes is a daunting task due to the complexities associated with waste stream composition, techno-economic analysis, and environmental assessment. Furthermore, the challenges to satisfy the desired product specifications, particularly in pharmaceuticals and specialty chemical industries, may also deter solvent recovery and reuse practices. To this end, this review presents a systems-level approach including various methodologies that can be implemented to design and evaluate efficient solvent recovery pathways.

Aqueous biphasic systems formed in (zwitterionic salt+inorganic salt) mixtures

The manuscript reports on a new class of aqueous biphasic systems (ABSs) formed in mixtures of inorganic salts (ISs) and zwitterionic salts (ZWSs). Aqueous ternary phase diagrams characterized by a binodal curve were determined for systems consisting of four ISs, K3PO4, K2HPO4, K2HPO4/KH2PO4, and K2CO3, and three structurally similar ZWSs differing in hydrophobicity. Comparison of phase behaviour of ABSs composed of ZWSs, ionic liquids (ILs) and zwitterions was provided. Potential of ZWSs based systems for extraction of aromatic molecules and amino acids, such as glycine, L-tryptophan, DL-phenylalanine, eugenol, and phenol was examined. Feasibility and limitations of isolation of products after partition and recovery of ZWS were discussed.

Synthesis and analysis of separation networks for the recovery of intracellular chemicals generated from microbial-based conversions

BACKGROUND

Bioseparations can contribute to more than 70% in the total production cost of a bio-based chemical, and if the desired chemical is localized intracellularly, there can be additional challenges associated with its recovery. Based on the properties of the desired chemical and other components in the stream, there can be multiple feasible options for product recovery. These options are composed of several alternative technologies, performing similar tasks. The suitability of a technology for a particular chemical depends on (1) its performance parameters, such as separation efficiency; (2) cost or amount of added separating agent; (3) properties of the bioreactor effluent (e.g., biomass titer, product content); and (4) final product specifications. Our goal is to first synthesize alternative separation options and then analyze how technology selection affects the overall process economics. To achieve this, we propose an optimization-based framework that helps in identifying the critical technologies and parameters.

RESULTS

We study the separation networks for two representative classes of chemicals based on their properties. The separation network is divided into three stages: cell and product isolation (stage I), product concentration (II), and product purification and refining (III). Each stage exploits differences in specific product properties for achieving the desired product quality. The cost contribution analysis for the two cases (intracellular insoluble and intracellular soluble) reveals that stage I is the key cost contributor (>70% of the overall cost). Further analysis suggests that changes in input conditions and technology performance parameters lead to new designs primarily in stage I.

CONCLUSIONS

The proposed framework provides significant insights for technology selection and assists in making informed decisions regarding technologies that should be used in combination for a given set of stream/product properties and final output specifications. Additionally, the parametric sensitivity provides an opportunity to make crucial design and selection decisions in a comprehensive and rational manner. This will prove valuable in the selection of chemicals to be produced using bioconversions (bioproducts) as well as in creating better bioseparation flow sheets for detailed economic assessment and process implementation on the commercial scale.

A roadmap for the synthesis of separation networks for the recovery of bio-based chemicals: Matching biological and process feasibility

Microbial conversion of renewable feedstocks to high-value chemicals is an attractive alternative to current petrochemical processes because it offers the potential to reduce net CO₂ emissions and integrate with bioremediation objectives. Microbes have been genetically engineered to produce a growing number of high-value chemicals in sufficient titer, rate, and yield from renewable feedstocks. However, high-yield bioconversion is only one aspect of an economically viable process. Separation of biologically synthesized chemicals from process streams is a major challenge that can contribute to >70% of the total production costs. Thus, process feasibility is dependent upon the efficient selection of separation technologies. This selection is dependent on upstream processing or biological parameters, such as microbial species, product titer and yield, and localization. Our goal is to present a roadmap for selection of appropriate technologies and generation of separation schemes for efficient recovery of bio-based chemicals by utilizing information from upstream processing, separation science and commercial requirements. To achieve this, we use a separation system comprising of three stages: (I) cell and product isolation, (II) product concentration, and (III) product purification and refinement. In each stage, we review the technology alternatives available for different tasks in terms of separation principles, important operating conditions, performance parameters, advantages and disadvantages. We generate separation schemes based on product localization and its solubility in water, the two most distinguishing properties. Subsequently, we present ideas for simplification of these schemes based on additional properties, such as physical state, density, volatility, and intended use. This simplification selectively narrows down the technology options and can be used for systematic process synthesis and optimal recovery of bio-based chemicals.

Antioxidative Effects and Inhibition of Human Low Density Lipoprotein Oxidation In Vitro of Polyphenolic Compounds in Flammulina velutipes (Golden Needle Mushroom)

Dietary polyphenolic compounds mediate polynomial actions in guarding against multiple diseases. Atherosclerosis is an oxidative stress driven pathophysiological complication where free radical induced oxidative modification of low density lipoprotein (LDL) plays the ground breaking role. Mushrooms have been highly regarded for possessing an antioxidant arsenal. Polyphenolic compounds present in dietary mushrooms seem pertinent in withstanding LDL oxidation en route to controlling atherosclerosis. In this study, the antioxidative effect of five solvent fractions consisting of methanol : dichloromethane (M : DCM), hexane (HEX), dichloromethane (DCM), ethyl acetate (EA), and aqueous residue (AQ) of Flammulina velutipes was evaluated. M : DCM fraction showed the most potent 2,2-diphenyl-1-picrylhydrazyl radical scavenging effect with IC₅₀ of 0.86 mg/mL and total phenolic content of 56.36 gallic acid equivalent/g fraction. In LDL oxidation inhibitory tests, M : DCM fraction at 1 µg/mL concentration mostly lengthened the lag time (125 mins) of conjugated diene formation and inhibited the formation of thiobarbituric acid reactive substances (48.71%, at 1 mg/mL concentration). LC-MS/MS analyses of M : DCM fraction identified the presence of polyphenolic substances protocatechuic acid, p-coumaric, and ellagic acid. These chain-breaking polyphenolics might impart the antioxidative effects of F. velutipes. Thus, mushroom-based dietary polyphenolic compounds might be implicated in slowing down the progression of atherosclerosis.

Inhibitory effect on in vitro LDL oxidation and HMG Co-A reductase activity of the liquid-liquid partitioned fractions of Hericium erinaceus (Bull.) Persoon (lion's mane mushroom)

Oxidation of low-density lipoprotein (LDL) has been strongly suggested as the key factor in the pathogenesis of atherosclerosis. Mushrooms have been implicated in having preventive effects against chronic diseases due especially to their antioxidant properties. In this study, in vitro inhibitory effect of Hericium erinaceus on LDL oxidation and the activity of the cholesterol biosynthetic key enzyme, 3-hydroxy-3-methyl glutaryl coenzyme A (HMG Co-A) reductase, was evaluated using five liquid-liquid solvent fractions consisting of methanol : dichloromethane (M : DCM), hexane (HEX), dichloromethane (DCM), ethyl acetate (EA), and aqueous residue (AQ). The hexane fraction showed the highest inhibition of oxidation of human LDL as reflected by the increased lag time (100 mins) for the formation of conjugated diene (CD) at 1 µg/mL and decreased production (68.28%, IC50 0.73 mg/mL) of thiobarbituric acid reactive substances (TBARS) at 1 mg/mL. It also mostly inhibited (59.91%) the activity of the HMG Co-A reductase at 10 mg/mL. The GC-MS profiling of the hexane fraction identified the presence of myconutrients: inter alia, ergosterol and linoleic acid. Thus, hexane fraction of Hericium erinaceus was found to be the most potent in vitro inhibitor of both LDL oxidation and HMG Co-A reductase activity having therapeutic potential for the prevention of oxidative stress-mediated vascular diseases.

Molecular aggregates in stable aqueous three-phase surfactant systems and their use in producing CdS nanowires

Aqueous three-phase surfactant systems (A3PS) are important, multicomponent, stable three-phase equilibria with coexisting forms in a common colloid solution, but have been largely ignored regarding further characterization and application. Mixing simple, commercially available, single-tailed anionic/nonionic or anionic/cationic surfactants in water can spontaneously produce stable A3PS with coexisting multiscale self-assembled structures including discs, lamellas, micelles and vesicles. As with conventional aqueous two-phase systems (A2PS), A3PS can be applied in partition and extraction processes. Here, the A3PS was also used as a mild media for one-step synthesis of multiscale CdS nanowires. Particularly, the A3PS does not change and simultaneously separates the CdS nanowires with the comparable size in one phase, which provides a facile strategy for collection of monodisperse nanomaterials. We expect that this present work can expand recognition of A3PS for use in theoretical and applied studies.

New tools for exploring "old friends-microbial lipases"

Fat-splitting enzymes (lipases), due to their natural, industrial, and medical relevance, attract enough attention as fats do in our lives. Starting from the paper that we write, cheese and oil that we consume, detergent that we use to remove oil stains, biodiesel that we use as transportation fuel, to the enantiopure drugs that we use in therapeutics, all these applications are facilitated directly or indirectly by lipases. Due to their uniqueness, versatility, and dexterity, decades of research work have been carried out on microbial lipases. The hunt for novel lipases and strategies to improve them continues unabated as evidenced by new families of microbial lipases that are still being discovered mostly by metagenomic approaches. A separate database for true lipases termed LIPABASE has been created recently which provides taxonomic, structural, biochemical information about true lipases from various species. The present review attempts to summarize new approaches that are employed in various aspects of microbial lipase research, viz., screening, isolation, production, purification, improvement by protein engineering, and surface display. Finally, novel applications facilitated by microbial lipases are also presented.

Electrophoretic transport of biomolecules across liquid-liquid interfaces

The mass transfer resistance of a liquid-liquid interface in an aqueous two-phase system composed of poly(ethylene glycol) and dextran is investigated. Different types of proteins and DNA stained with fluorescent dyes serve as probes to study the transport processes close to the interface. A microfluidic device is employed to enable the electrophoretic transport of biomolecules from one phase to another. The results obtained for proteins can be explained solely via the different electrophoretic mobilities and different affinities of the molecules to the two phases, without any indications of a significant mass transfer resistance of the liquid-liquid interface. By contrast, DNA molecules adsorb to the interface and only desorb under an increased electric field strength. The desorption process carries the signature of a thermally activated escape from a metastable state, as reflected in the exponential decay of the fluorescence intensity at the interface as a function of time.

Multistage magnetic and electrophoretic extraction of cells, particles and macromolecules

Improved techniques for separating cells, particles, and macromolecules (proteins) are increasingly important to biotechnology because separation is frequently the limiting factor for many biological processes. Manufacturers of new enzymes and pharmaceutical products require improved methods for recovering intact cells and intracellular products. Similarly isolation, purification, and concentration of many biomolecules produced in fermentation processes is extremely important. Often such downstream processing contributes a large portion of the product cost. In conventional methods like centrifugation and even modern methods like chromatography, scale-up problems are enormous, making them uneconomical and prohibitively expensive unless the product is of very high value. Therefore there has been a need for efficient and economical alternative approaches to bioseparation processes to eliminate, reduce, or facilitate solids handling. Magnetic and electric field assisted separations may hold considerable potential for providing a future major improvement in bioseparation technology. In the present review the merits and demerits of the existing methods are discussed. We present mainly our own research on the development of unified multistage extraction processes that are versatile enough to handle cells and particles as well as macromolecules as described below. We describe multistage methods, namely ADSEP (Advanced Separator), MAGSEP (Magnetic Separator), and ELECSEP (Electrophoretic Separator), for quantitatively separating cells, particles, and solutes by using magnetically and electrophoretically assisted extraction processes. To the best of our knowledge, multistage magnetic and electrophoretic separations have not been reported in the earlier literature. The theoretical underpinnings of these separations are crucial to their success and to the identification of their advantages over other separation processes in particular applications. Hence mathematical modeling is stressed here, presenting our own models while also reviewing models reported in the literature. We also present suggestions for future work while analyzing the scale-up and economic aspects of these extraction processes. Commercial uses of the magnetic and electrophoretic processes, having both ground- and space-based research elements, also are presented in this review.

Hydroxypropyl cellulose/poly(ethylene glycol)-co-poly(propylene glycol) aqueous two-phase systems: System characterization and partition of cells and proteins

Novel aqueous polymeric two-phase systems are described. These systems are formed by mixing hydroxypropyl cellulose (molecular mass 100,000, trade name Klucel L) with poly(ethylene glycol)-co-poly(propylene glycol) copolymer [molecular mass 6,500, poly(propylene glycol) content 50% w/w, trade name Pluronic P105], in a saline buffer. The phase diagram was measured and the interfacial tensions, phase separation times, and lower phase viscosities of three phase systems having constant Pluronic P105 concentration but varying in Klucel L concentration were determined. The partition behavior of a representative cell, bacterium, and protein and the affinity ligand-mediated alteration in the partition behavior of a protein from a yeast extract protein mixture were also characterized. The results suggest that Klucel L/Pluronic P105 phase systems may be cost-effective substitutes for, or complements to, existing aqueous polymeric phase systems. The physical characterization and representative partition data reported here should facilitate application of these new systems.