Isoelectric precipitation of soybean protein using carbon dioxide as a volatile acid

Protein Recovery from Underutilised Marine Bioresources for Product Development with Nutraceutical and Pharmaceutical Bioactivities

The global demand for dietary proteins and protein-derived products are projected to dramatically increase which cannot be met using traditional protein sources. Seafood processing by-products (SPBs) and microalgae are promising resources that can fill the demand gap for proteins and protein derivatives. Globally, 32 million tonnes of SPBs are estimated to be produced annually which represents an inexpensive resource for protein recovery while technical advantages in microalgal biomass production would yield secure protein supplies with minimal competition for arable land and freshwater resources. Moreover, these biomaterials are a rich source of proteins with high nutritional quality while protein hydrolysates and biopeptides derived from these marine proteins possess several useful bioactivities for commercial applications in multiple industries. Efficient utilisation of these marine biomaterials for protein recovery would not only supplement global demand and save natural bioresources but would also successfully address the financial and environmental burdens of biowaste, paving the way for greener production and a circular economy. This comprehensive review analyses the potential of using SPBs and microalgae for protein recovery and production critically assessing the feasibility of current and emerging technologies used for the process development. Nutritional quality, functionalities, and bioactivities of the extracted proteins and derived products together with their potential applications for commercial product development are also systematically summarised and discussed.

Status of Plant Protein-Based Green Scaffolds for Regenerative Medicine Applications

In recent decades, regenerative medicine has merited substantial attention from scientific and research communities. One of the essential requirements for this new strategy in medicine is the production of biocompatible and biodegradable scaffolds with desirable geometric structures and mechanical properties. Despite such promise, it appears that regenerative medicine is the last field to embrace green, or environmentally-friendly, processes, as many traditional tissue engineering materials employ toxic solvents and polymers that are clearly not environmentally friendly. Scaffolds fabricated from plant proteins (for example, zein, soy protein, and wheat gluten), possess proper mechanical properties, remarkable biocompatibility and aqueous stability which make them appropriate green biomaterials for regenerative medicine applications. The use of plant-derived proteins in regenerative medicine has been especially inspired by green medicine, which is the use of environmentally friendly materials in medicine. In the current review paper, the literature is reviewed and summarized for the applicability of plant proteins as biopolymer materials for several green regenerative medicine and tissue engineering applications.

Role of the Drying Technique on the Low-Acyl Gellan Gum Gel Structure: Molecular and Macroscopic Investigations

The effect of three drying processes (freeze, oven and supercritical CO₂ drying) on CP Kelco low-acyl gellan gum gel was investigated, highlighting the role of the water removal mechanism (i.e. sublimation, evaporation and solvent replacement/extraction) and the process parameters on the gel structure, rather than focusing on the drying kinetics. It is the first time that a research paper not only compares the drying methods but also discusses and investigates how the molecular and macroscopic levels of gellan gum are affected during drying. Specifically, the dried gel structures were characterised by bulk density and shrinkage analyses as well as scanning electron microscope (SEM) and micro-computed tomography (μCT) microscopy. Micro-differential scanning calorimetry (μDSC) was used in a novel way to investigate the effect of the drying technique on the polymer disorder chains by partial melting of the gel. The resulting water uptake during rehydration was influenced by the obtained dried structure and, therefore, by the employed drying process. It was found that freeze-dried (FD) structures had a fast rehydration rate, while both oven-dried (OD) and supercritical CO₂-dried (scCO₂D) structures were slower. After 30 min, FD samples achieved a normalised moisture content (NMC) around 0.83, whereas OD and scCO₂D samples around 0.33 and 0.19, respectively. In this context, depending on the role of the specific hydrocolloid in food (i.e. gelling agent, thickener, carrier), one particular dried-gel structure could be more appropriate than another. Graphical abstractFrom left to right: unprocessed hydrogels; μ-CT images of dried gels and unprocessed hydrogel; DSC curves after drying process.

Pressurized CO2 as a carboxylating agent for the biocatalytic ortho-carboxylation of resorcinol

The utilization of gaseous carbon dioxide instead of bicarbonate would greatly facilitate process development for enzyme catalyzed carboxylations on a large scale. As a proof-of-concept, 1,3-dihydroxybenzene (resorcinol) was carboxylated in the ortho-position using pressurized CO₂ (∼30-40 bar) catalyzed by ortho-benzoic acid decarboxylases with up to 68% conversion. Optimization studies revealed tight pH-control and enzyme stability as the most important determinants.

Biomedical applications of soy protein: A brief overview

Soy protein (SP) based materials are gaining increasing interest for biomedical applications because of their tailorable biodegradability, abundance, being relatively inexpensive, exhibiting low immunogenicity, and for being structurally similar to components of the extracellular matrix (ECM) of tissues. Analysis of the available literature indicates that soy protein can be fabricated into different shapes, being relatively easy to be processed by solvent or melt based techniques. Furthermore soy protein can be blended with other synthetic and natural polymers and with inorganic materials to improve the mechanical properties and the bioactive behavior for several demands. This review discusses succinctly the biomedical applications of SP based materials focusing on processing methods, properties and applications highlighting future avenues for research.

Biocatalytic carboxylation of phenol derivatives: kinetics and thermodynamics of the biological Kolbe-Schmitt synthesis

Microbial decarboxylases, which catalyse the reversible regioselective ortho-carboxylation of phenolic derivatives in anaerobic detoxification pathways, have been studied for their reverse carboxylation activities on electron-rich aromatic substrates. Ortho-hydroxybenzoic acids are important building blocks in the chemical and pharmaceutical industries and are currently produced via the Kolbe-Schmitt process, which requires elevated pressures and temperatures (≥ 5 bar, ≥ 100 °C) and often shows incomplete regioselectivities. In order to resolve bottlenecks in view of preparative-scale applications, we studied the kinetic parameters for 2,6-dihydroxybenzoic acid decarboxylase from Rhizobium sp. in the carboxylation- and decarboxylation-direction using 1,2-dihydroxybenzene (catechol) as starting material. The catalytic properties (K(m), V(max)) are correlated with the overall thermodynamic equilibrium via the Haldane equation, according to a reversible random bi-uni mechanism. The model was subsequently verified by comparing experimental results with simulations. This study provides insights into the catalytic behaviour of a nonoxidative aromatic decarboxylase and reveals key limitations (e.g. substrate oxidation, CO2 pressure, enzyme deactivation, low turnover frequency) in view of the employment of this system as a 'green' alternative to the Kolbe-Schmitt processes.

Soy protein/soy polysaccharide complex nanogels: folic acid loading, protection, and controlled delivery

In this study, we developed a facile approach to produce nanogels via self-assembly of folic acid, soy protein, and soy polysaccharide. High-pressure homogenization was introduced to break down the original aggregates of soy protein, which benefits the binding of soy protein with soy polysaccharide and folic acid at pH 4.0. After a heat treatment that causes the soy protein denaturation and gelation, folic acid-loaded soy protein/soy polysaccharide complex nanogels were fabricated. The nanogels have a polysaccharide surface that makes the nanogels dispersible in acidic conditions where folic acid is insoluble and soy protein forms precipitates after heating. More importantly, the protein and polysaccharide can inhibit the reactions between dissolved oxygen and folic acid during UV irradiation. After the preparation and storage of the nanogels in the presence of heat, oxygen, and light in acidic conditions, most of the folic acid molecules in the nanogels remain in their natural structure and can be released rapidly at neutral pH, that is, in the intestine. Because most food and beverages are acidic, the nanogels are a suitable delivery system of folic acid in food and beverages.

Stable nano-sized emulsions produced from soy protein and soy polysaccharide complexes

In this research, a simple, green and effective strategy was developed to produce long-term stable oil in water emulsion from soy protein and soy polysaccharide. Soy protein and soy polysaccharide formed dispersible complexes at pH around 3.25 aqueous solution through electrostatic and hydrophobic interactions. A high pressure homogenization produced the protein/polysaccharide complex emulsion having a droplet size about 250 nm. A heat treatment of the emulsion resulted in the protein denaturation, forming irreversible oil-water interfacial films composed of soy protein/soy polysaccharide complexes. The droplets of the emulsion were characterized by dynamic light scattering, ζ-potential, transmission electron microscopy, polysaccharide digestion via pectinase, and confocal laser scanning microscopy observation via dual fluorescence probes. As a result of the polysaccharide being fixed on the droplet surface, the emulsions exhibited long-term stability in the media containing pH values of 2-8 and 0.2 mol/L NaCl. The stable soy protein/soy polysaccharide complex emulsion is a suitable food-grade delivery system in which lipophilic bioactive compounds can be encapsulated.

Carbon dioxide induced silk protein gelation for biomedical applications

We present a novel method to fabricate silk fibroin hydrogels using high pressure carbon dioxide (CO(2)) as a volatile acid without the need for chemical cross-linking agents or surfactants. The simple and efficient recovery of CO(2) post processing results in a remarkably clean production method offering tremendous benefit toward materials processing for biomedical applications. Further, with this novel technique we reveal that silk protein gelation can be considerably expedited under high pressure CO(2) with the formation of extensive β-sheet structures and stable hydrogels at processing times less than 2 h. We report a significant influence of the high pressure CO(2) processing environment on silk hydrogel physical properties such as porosity, sample homogeneity, swelling behavior and compressive properties. Microstructural analysis revealed improved porosity and homogeneous composition among high pressure CO(2) specimens in comparison to the less porous and heterogeneous structures of the citric acid control gels. The swelling ratios of silk hydrogels prepared under high pressure CO(2) were significantly reduced compared to the citric acid control gels, which we attribute to enhanced physical cross-linking. Mechanical properties were found to increase significantly for the silk hydrogels prepared under high pressure CO(2), with a 2- and 3-fold increase in the compressive modulus of the 2 and 4 wt % silk hydrogels over the control gels, respectively. We adopted a semiempirical theoretical model to elucidate the mechanism of silk protein gelation demonstrated here. Mechanistically, the rate of silk protein gelation is believed to be a function of the kinetics of solution acidification from absorbed CO(2) and potentially accelerated by high pressure effects. The attractive features of the method described here include the acceleration of stable silk hydrogel formation, free of residual mineral acids or chemical cross-linkers, reducing processing complexity, and avoiding adverse biological responses, while providing direct manipulation of hydrogel physical properties for tailoring toward specific biomedical applications.

Fractionation of whey protein isolate with supercritical carbon dioxide to produce enriched α-lactalbumin and β-lactoglobulin food ingredients

An environmentally friendly protein fractionation process using supercritical carbon dioxide (SCO(2)) as an acid was developed to produce enriched α-lactalbumin (α-LA) and β-lactoglobulin (β-LG) fractions from whey protein isolate solutions containing from 2 to 10% WPI. This study investigated the effects of pH, temperature, WPI concentration, and residence time on the precipitation kinetics and recovery yields of individual whey proteins and the relative enrichment and composition of both protein fractions. At 5.5-34 MPa and 60-65 °C, solubilized SCO(2) decreased solution pH and induced the formation and precipitation of α-LA aggregates. Gel electrophoresis and HPLC of the enriched fractions demonstrated the production of ≥ 60% pure α-LA, and ≥ 70% pure β-LG, under various operating conditions, from WPI containing ∼57% β-LG and 21% α-LA. The enriched fractions are ready-to-use food ingredients with neutral pH, untainted by acids and contaminants.

Fractionation of whey protein isolate with supercritical carbon dioxide-process modeling and cost estimation

An economical and environmentally friendly whey protein fractionation process was developed using supercritical carbon dioxide (sCO(2)) as an acid to produce enriched fractions of α-lactalbumin (α-LA) and β-lactoglobulin (β-LG) from a commercial whey protein isolate (WPI) containing 20% α-LA and 55% β-LG, through selective precipitation of α-LA. Pilot-scale experiments were performed around the optimal parameter range (T = 60 to 65 °C, P = 8 to 31 MPa, C = 5 to 15% (w/w) WPI) to quantify the recovery rates of the individual proteins and the compositions of both fractions as a function of processing conditions. Mass balances were calculated in a process flow-sheet to design a large-scale, semi-continuous process model using SuperproDesigner® software. Total startup and production costs were estimated as a function of processing parameters, product yield and purity. Temperature, T, pressure, P, and concentration, C, showed conflicting effects on equipment costs and the individual precipitation rates of the two proteins, affecting the quantity, quality, and production cost of the fractions considerably. The highest α-LA purity, 61%, with 80% α-LA recovery in the solid fraction, was obtained at T = 60 °C, C = 5% WPI, P = 8.3 MPa, with a production cost of $8.65 per kilogram of WPI treated. The most profitable conditions resulted in 57%-pure α-LA, with 71% α-LA recovery in the solid fraction and 89% β-LG recovery in the soluble fraction, and production cost of $5.43 per kilogram of WPI treated at T = 62 °C, C = 10% WPI and P = 5.5 MPa. The two fractions are ready-to-use, new food ingredients with a pH of 6.7 and contain no residual acid or chemical contaminants.

Novel dense CO2 technique for beta-galactosidase immobilization in polystyrene microchannels

In this study we design new fabrication techniques and demonstrate the potential of using dense CO2 for facilitating crucial steps in the fabrication of polymeric lab-on-a-chip microdevices by embedding biomolecules at temperatures well below the polymer's glass transition temperature (T(g)). These new techniques are environmentally friendly and done without the use of a clean room. Carbon dioxide at 40 degrees C and between 4.48 and 6.89 MPa was used to immobilize the biologically active molecule, beta-galactosidase (beta-gal), on the surface of polystyrene microchannels. To our knowledge, this is the first time dense CO2 has been used to directly immobilize an enzyme in a microchannel. beta-gal activity was maintained and shown via a fluorescent reaction product, after enzyme immobilization and microchannel capping by the designed fabrication steps at 40 degrees C and pressures up to 6.89 MPa.

Application of supercritical fluid to preparation of powders of high-molecular weight drugs for inhalation

The application of supercritical carbon dioxide to particle design has recently emerged as a promising way to produce powders of macromolecules such as proteins and genes. Recently, an insulin powder for inhalation was approved by authorities in Europe and the USA. Other macromolecules for inhalation therapy will follow. In the 1990s proteins were precipitated with supercritical CO(2) from solutions in an organic solvent such as dimethylsulfoxide, which caused significant unfolding of protein. Since 2000, aqueous solutions of proteins and genes have generally been used with a cosolvent such as ethanol to precipitate in CO(2). Operating conditions such as temperature, pressure, flow rates, and concentration of ingredients affect the particle size and integrity of proteins or genes. By optimizing these conditions, the precipitation of proteins and genes with supercritical CO(2) is a promising way to produce protein and gene particles for inhalation.

Stabilization of IgG by supercritical fluid drying: Optimization of formulation and process parameters

The aim of this study was to stabilize human serum immunoglobulin G (IgG) by a supercritical fluid (SCF) drying process. Solutions containing IgG (20mg/ml) and trehalose or hydroxypropyl-beta-cyclodextrin in a 1:4 (w/w) ratio were sprayed into a SCF phase consisting of CO(2) and ethanol at 100bar and 37 degrees C. Initially, a set of drying conditions previously developed to successfully stabilize lysozyme and myogobin formulations was used [N. Jovanović, A. Bouchard, G.W. Hofland, G.J. Witkamp, D.J.A. Crommelin, W. Jiskoot, Eur. J. Pharm. Sci. 27 (2006) 336-345]. Dried formulations were analyzed by Karl Fisher titration, scanning electron microscopy, X-ray powder diffraction, and modulated DSC. Protein structure in the solid-state was studied by FTIR and after reconstitution by UV/Vis, circular dichroism and fluorescence spectroscopy, GPC and SDS-PAGE. When IgG was dried under the above-mentioned conditions, substantial amounts of insoluble aggregates were formed. Addition of buffer helped to reduce the fraction of insoluble material but not of soluble aggregates. Full stabilization could be achieved by adjusting the process conditions: drying without ethanol while keeping the other conditions the same, or drying with ethanol at a temperature below the critical point (20 degrees C). In conclusion, it is possible to stabilize human IgG by SCF drying provided that the formulation and process conditions are tailored to meet the specific requirements of the protein.

A method for lipase co-precipitation in a biodegradable protein matrix

This article presents a novel method for immobilization of active ingredients. The method is based on CO(2) aided active ingredient co-precipitation with glycinin, a biodegradable protein matrix from edible soybean protein. Glycinin precipitates abundantly under isoelectric conditions and serves as the matrix within which the active substance is trapped during the precipitation process. The enzyme lipase from Candida rugosa was successfully co-precipitated into the protein pellet to prove the principle. It was shown that the lipase within the co-precipitate retained lipase and esterase activity under different pH conditions. In some cases the activity was even higher than the activity of crude lipase, possibly due to the protective role of the matrix protein. Due to the retained lipase activity and food-grade quality of the binary precipitate, it has potential of being used in the food or pharmaceutical industry. Additional quality of the binary precipitate is the potentially significantly reduced downstream processing due to the fact that no organic solvents or precipitants were used in the precipitation process.

Determination of extracellular and intracellular pH of Bacillus subtilis suspension under CO2 treatment

In this study, we consider the effect of carbon dioxide (CO(2)) on the intracellular and extracellular pH of a saline solution of a test-microorganisms Bacillus subtilis. The cytoplasmatic pH was determined by means of a flow cytometry with the fluorescent probe 5(and 6-)-carboxyfluorescein ester (cFSE). The physiological suspension of cells with the addition of the probe was first exposed to high pressure CO(2) for 5 min at different temperatures. The flow cytometry analysis indicated an intracellular depletion inside the cell caused by the action of CO(2), down to 3, the depletion being dependent on inactivation ratio. In addition, the extracellular pH was determined theoretically by means of the statistical associated fluid theory equation of state (SAFT EOS): it was demonstrated that CO(2) under pressure dissolves into liquid phase and acidifies the medium down to 3 at 80 bar and 303.15K. The results show a strong influence between extracellular and intracellular pH, and lead to the conclusion that a strong reduction of the pH homeostasis of the cell can be claimed as one of the most probable cause of inactivation of CO(2) pasteurization.

Alternative bioseparation operations: life beyond packed-bed chromatography

Chromatography is undoubtedly the workhorse of downstream processes, affording high resolution for bioseparations. At the same time, it has the notoriety of being the single largest cost center in downstream processing and of being a low-throughput operation. Consequently, 'chromatography alternatives' are an attractive proposition, even if only a reduction in the extent of use of packed beds can be realized. This paper reviews the current state of unit operations posing as chromatography alternatives--including membrane filtration, aqueous two-phase extraction, three-phase partitioning, precipitation, crystallization, monoliths and membrane chromatography--and their potential to do the unthinkable.

Preparation, optimization, and structures of cross-linked enzyme aggregates (CLEAs)

The broad applicability of the cross-linking of enzyme aggregates to the effective immobilisation of enzymes is demonstrated and the influence of many parameters on the properties of the resulting CLEAs is determined. The relative simplicity of the operation ideally lends itself to high-throughput methodologies. The aggregation method was improved up to 100% activity yield for any enzyme. For the first time, the physical structures of CLEAs are elucidated.

Carbon dioxide induced soybean protein precipitation: protein fractionation, particle aggregation, and continuous operation

A novel protein fractionation technique using a volatile electrolyte has been developed. Carbon dioxide was used to isoelectrically precipitate 80% and 95% pure glycinin and beta-conglycinin fractions from soybean isolate. The protein fractions precipitated as primary particles 0.2-0.3 microm in diameter, which under optimum conditions may be recovered as aggregates up to 500 microm in diameter. The dependency of protein fractionation efficiency on aggregate settling rates has been demonstrated. The isoelectric points of the two main soybean fractions, glycinin and beta-conglycinin, were calculated to be pH 5.2 and 4.95, respectively. Solution pH was accurately controlled by pressure in the isoelectric pH range of the different soybean protein fractions, and a pH "overshoot" was eliminated. Volatile electrolyte technology was also applied to a continuous process in order to eliminate the particle recovery concerns associated with batch precipitation and to demonstrate the potential for scale-up. Glycinin was effectively recovered on-line (94% glycinin recovery) with a purity approaching that of the batch process (95%).

Fractionation of soybean proteins with pressurized carbon dioxide as a volatile electrolyte

Fractionation of specific proteins from plant material is a complex and involved science, yet pure protein extracts are in high demand by a wide range of food and pharmaceutical industries. In this study carbon dioxide has been used as a volatile electrolyte to isoelectrically precipitate two major protein constituents of soybean. Carbon dioxide was shown to be effective in purifying glycinin and beta-conglycinin in a three-step process as 95% and 80% concentrated fractions with precipitation yields of 28% and 21%, respectively. Recycling of the mixed precipitate of the intermediary step enables complete separation into the concentrated fractions. Fractionation acidity was precisely controlled by a simple modification of pressure. In addition, the occurrence of a pH overshoot was prevented at any point in the fractionation vessel, as the pH minimum was defined by its equilibrium relationship with carbon dioxide operating pressure. The removal of the glycinin precipitate was an important factor in the purification procedure. The yield of the individual concentrated glycinin and beta-conglycinin precipitate fractions was a function of carbon dioxide pressure, extract concentration and, to a much lesser extent, temperature.