Freeze-drying Step Research Articles

High entropy 2D metals sulfides: Fast synthesis, exfoliation and electrochemical activity in overall water splitting at alkaline pH

Novel simple and efficient method for synthesis of 2D high entropy sulfides of iron group metals is described. The method utilizes inorganic salts as precursors and CS2 as a sulfurizing agent, which makes it possible to achieve high entropy composition through combination of freezing of the precursor solution, subsequent freeze-drying step, sulfurization, and exfoliation in liquid nitrogen. The created material was investigated as a catalyst for electrochemical water splitting at different pH. Measured overpotentials at 10 and 100 mA*cm−2 current densities for hydrogen evolution reaction (HER) were found to be 49 and 315 mV respectively, while for oxygen evolution reaction (OER) theoverpotentials required for reaching 10 and 100 mA*cm−2 current densities were 370 and 591 mV respectively, both in 1 M KOH solution. The Tafel slopes for HER were found to be 235, 105, and 111 mV/dec in basic, neutral, and acidic conditions, respectively, while only 63 mV/dec for OER in basic conditions. The calculated values of the turnover frequency were 0.62 s−1 for HER and 0.10 s−1 for OER. We also confirmed the key role of high entropy in the catalytic activity of the material by excluding individual elements from the composition of the HES.

Formulation of protein-loaded nanoparticles via freeze-drying.

Several nanotechnology-based formulation strategies have been reported for the oral administration of biological drugs. However, a prerequisite often overlooked in developing these formulations is their adaptation to a solid dosage form. This study aimed to incorporate a freeze-drying step, using either mannitol or sucrose laurate (SLAE), into the formulation of new insulin-zinc nanocomplexes to render them resistant to intestinal fluids while maintaining a high protein loading. The resulting freeze-dried insulin-zinc nanocomplexes exhibited physicochemical properties consistent with the target product profile, including a particle size of ∼ 100nm, a zeta potential close to neutrality (∼ -15 mV) and a high association efficiency (> 90%). Importantly, integrating the freeze-drying step in the formulation significantly improved the colloidal stability of the system and preserved the stability of the insulin molecules. Results from in vitro and in vivo studies indicated that the insulin activity remained fully retained throughout the entire formulation and freeze-drying processes. In brief, we present a novel protein formulation strategy that incorporates a critical freeze-drying step, resulting in a dry powder enabling efficient protein complexation with zinc and optimized for oral administration.

Construction of carbon and nitride double vacancy defects on ultrathin porous g-C3N4 nanosheets assisted by freeze-drying for enhanced photocatalysis

Graphitic carbon nitride based photocatalysts have been found extensive application in the degradation of antibiotics and organic pollutants. However, the insufficient of surface active sites and the low efficiency of photogenerated charge carriers separation hinder the development. Herein, ultrathin porous polymer carbon nitride nanosheets (PCNS-F) with carbon and nitride double vacancy defects were successfully fabricated. The facile freeze-drying step, following solvent-thermal treatment and preceding the thermal etching process, stands as a critical step for triggering vacancy generation and adjusting the carbon/nitride ratio. The optimized PCNS-F photocatalyst exhibits an ultrathin structure featuring a substantial abundance of defects in a porous state, resulting in exceptional structural characteristics (183.3 m² g-1, 0.84 cm³ g-1). Surface defect sites increase, and the efficient separation and transfer of photo-generated charge carriers are promoted with the introduction of a suitable vacancy density. PCNS-F demonstrated outstanding photocatalytic degradation performances for tetracycline (81.7 %) and methylene blue (97.7 %) under visible light irradiation for 2 h, which are 10 and 7.2 times higher than those of bulk g-C3N4. The active species of ∙O2- was confirmed to play a major role in the photodegradation process. This work provides a mild approach for engineering carbon and nitride double vacancy defects on g-C3N4 nanosheets, accompanied by tuning carbon/nitride ratio, to effectively eliminate pollutants and cleanse the environment.’

Removal of dyes from aqueous media using environmentally friendly aerogels based on chitosan

According to the World Health Organization, between 17% and 20% of water pollution is caused by dye treatments in the textile industry, which makes the development of efficient technologies for its removal essential. Environmentally friendly adsorbent materials, such as aerogels, can be effectively used in adsorption processes involving water remediation because of their high specific surface area and the possibility of an easy separation from the contaminated solutions. In this work, aerogels were obtained by a simple procedure that includes the cross-linking of chitosan with glutaraldehyde, followed by a freeze-drying step to eliminate water by water sublimation. The obtained aerogels presented low density (0.049–0.083 g/cm3), a three-dimensional skeletal structure that provides them with high porosity, acceptable swelling capacity and good dimensional stability. FTIR and X-Ray analysis were used to identify aerogels’ chemical structure and dynamic-mechanical analysis to complement the characterization of these materials. Selected formulations were also tested as adsorbents of Congo Red in aqueous media. The adsorption results demonstrated that the aerogels adsorption capacity strongly depended not only on the crosslinking agent content but also on the amount of chitosan in the initial solution used in their synthesis. Moreover, preliminary thermodynamic studies of the adsorption process indicate that both adsorption rate and aerogel sorption capacity increase with increasing temperature.

3D Lightweight Interconnected Melamine Foam Modified with Hollow CoFe2O4/MXene toward Efficient Microwave Absorption.

Considering the increasing severity of electromagnetic wave pollution, the development of high-performance low-filler-content microwave absorbers possessing wide frequency bands and strong absorption for practical applications is a demanding research hotspot. In this study, from the perspectives of the electromagnetic component coordination and structural design, a three-dimensional (3D) interconnected CoFe2O4/MXene-melamine foam (MF) was constructed via simple impregnation and a single freeze-drying step. By changing the absorber (CoFe2O4/MXene) concentration, the pore opening and electromagnetic properties of the 3D foams can be effectively adjusted. When the absorber concentration is sufficiently high to clog the internal pores, the microwave absorption is hindered. When the filler (CoFe2O4/MXene-MF) content is just ∼5.8 wt % (at a density of ∼33.3 mg cm-3), a minimum reflection loss (RLmin) of -72.1 dB is achieved at a matching thickness of 3.32 mm, and an effective absorption bandwidth (4.54 GHz) covering the whole X band is achieved at a thickness of 3 mm. CoFe2O4/MXene-MF, which possesses a 3D porous electromagnetic network structure, optimizes impedance matching and enhances multiple polarization relaxations and reflections/scattering, resulting in superior absorption capabilities. In particular, the continuous network structure ensures the uniform distribution of electromagnetic fields in the microstructure, achieving high absorption at low filler contents. This work provides a reference for subsequent 3D absorber concentration studies and a novel engineering strategy for preparing a low-filler-content, lightweight, and efficient electromagnetic wave absorber, which could be applied in the fields of radar security and information communications.

Novel Efficient Physical Technologies for Enhancing Freeze Drying of Fruits and Vegetables: A Review.

Drying is the main technical means of fruit and vegetable processing and storage; freeze drying is one of the best dehydration processes for fruit and vegetables, and the quality of the final product obtained is the highest. The process is carried out under vacuum and at low temperatures, which inhibits enzymatic activity and the growth and multiplication of micro-organisms, and better preserves the nutrient content and flavor of the product. Despite its many advantages, freeze drying consumes approximately four to ten times more energy than hot-air drying, and is more costly, so freeze drying can be assisted by means of highly efficient physical fields. This paper reviews the definition, principles and steps of freeze drying, and introduces the application mechanisms of several efficient physical fields such as ultrasonic, microwave, infrared radiation and pulsed electric fields, as well as the application of efficient physical fields in the freeze drying of fruits and vegetables. The application of high efficiency physical fields with freeze drying can improve drying kinetics, increase drying rates and maintain maximum product quality, providing benefits in terms of energy, time and cost. Efficient physical field and freeze drying technologies can be well linked to sustainable deep processing of fruit and vegetables and have a wide range of development prospects.

New plasma protein C and protein S concentrate: A synergy for therapeutic purposes.

Deficiencies of protein C (PC) or protein S (PS) are rare diseases, characterized by mutations in the PC or PS genes, which encode plasma serine proteases with anti-coagulant activity. Severe PC or PS deficiencies manifest in early life as neonatal purpura fulminans, a life-threatening heamorrhagic condition requiring immediate treatment. First-line treatment involves replacement therapy, followed by maintenance with anti-coagulants. Replacement therapy with specific protein concentrates is currently only limited to PC, and therefore, a PC + PS concentrate represents a useful addition to therapeutic options, particularly for severe PS deficiency. Further, the production of a PC + PS concentrate from unused plasma fractionation intermediates would impact favourably on manufacturing costs, and consequently therapy prices for patients and health systems. Several chromatographic runs were performed on the same unused plasma fractionation intermediates using different supports to obtain a PC/PS concentrate. The best chromatographic mediums were chosen, in terms of specific activity and recovery. A full process of purification including virus inactivation/removal and lyophilization steps was set up. The final freeze-dried product had a mean PC concentration of 47.75 IU/mL with 11% of PS, and a mean specific activity of 202.5 IU/mg protein, corresponding to over 12,000-fold purification from plasma. The development of a novel concentrated PC/PS mixture obtained from a waste fraction of other commercial products could be used for its potential therapeutic role in the management of neonatal purpura fulminans pathology.

Construction of Marigold-like Poly(vinyl alcohol) Microspheres for Catalytic Microreactors.

It has long been pursued to develop polymer microspheres with various special morphologies and structures for better results in applications such as catalysis, drug delivery, and bioscaffolds. However, it remains a challenge to develop a facile method to produce poly(vinyl alcohol) (PVA) microspheres with special morphologies. Herein, a micron-sized marigold-like poly(vinyl alcohol) (CE-PVATPA) microsphere was engineered and fabricated by a feasible strategy, that is, emulsification-cross-linking, freeze-drying, and secondary acetal reaction steps. The morphological evolution of microspheres was systematically investigated under different conditions, and the procedure of constructing PVA microspheres with stabilizing marigold-like structures was proposed. More importantly, a specially structured PVA microsphere microreactor synergistically loading palladium metal nanoparticles (CE-PVATPA@Pd) for the heterogeneous catalyst 4-nitrophenol (4-NP) could be further demonstrated, which indicated high catalytic activity and excellent recyclability. The resultant stabilized fabricating method is promising to provide valuable guidance for the design and fabrication of a high-performance PVA microsphere microreactor.

Method development and quantification of all B vitamins and selected biosynthetic precursors in winter and spring samples from the North Sea and de novo synthesized by Vibrio campbellii

The simultaneous analysis of B vitamins and biosynthetic precursors in seawater is of great interest as it gives a better insight into the fluctuations of their availability for marine organisms and thus allows us to better understand the nature of interactions between prototrophic and auxotrophic organisms. The analysis of these micronutrients is challenging, as they are usually present in the marine environment in minuscule quantities only. Additionally, some of them are light- and heat-sensitive which complicates their handling. To meet these circumstances, the presented sample work-up method for seawater started with a freeze-drying step for volume reduction of the sample. This shortened the duration of the subsequent solid phase extraction and resulted in an increase in recovery. When comparing three solid phase extraction materials (C18, HLB, PPL), PPL was found to be the most suitable. This method was applied for the quantification of all eleven B vitamins and six precursors in waters from the southern North Sea taken in winter and spring. Quantification was performed by LC-MS. The winter samples showed higher concentrations for nearly all analytes, in contrast to the uptake of most nutrients at the beginning of a potential algal bloom in spring and low analyte concentrations in springtime waters. In addition, the marine bacterium Vibrio campbellii, prototrophic for most B vitamins, was cultivated without the addition of B vitamins in order to measure them intra- and extracellularly during growth. In most cases, intracellular concentrations per cell decreased towards the end of the exponential growth phase, while extracellular concentrations increased. Extracellular B vitamin and precursor concentration measurements show that V. campbellii is in exchange with its environment and thereby possibly enables growth of B vitamin auxotrophs in the environment.

The effect of processing design and the stabilizing effect of nanostructures on the swelling and adsorption properties of polyvinylpyrrolidone macroporous ferrogels obtained through a cryogenic route

AbstractThis paper reports the synthesis of macroporous polyvinylpyrrolidone (PVP) hydrogels modified with in‐situ generated magnetic nanoparticles (NPs). The hydrogels were formed by an optimized thermally induced crosslinking route, initiated by the presence of ammonium persulfate, whereas the macroporosity was created through a cryogenic technique. Crosslinking stabilizes the three dimensional (3D) gel structure, allowing the replacement of expensive and time‐consuming lyophilization steps in favor of simpler drying procedures at atmospheric pressure. The in‐situ formation of iron oxide NPs (IONPs) was achieved through oxide precursors impregnation followed by precipitation of the IONPs in the highly swellable hydrogels. This reaction was performed by addressing two strategies, namely, before or after cryogenic processing, to evaluate its effect on the final swelling and adsorption properties of the gel matrices. It is demonstrated that the inclusion of the magnetic NPs before cryo‐structuring allows the stabilization of the gel against collapse, favoring the conservation of a highly swellable environment. The synergy between the adsorption capacity of the IONPs and the high swelling of the macroporous structure allows obtaining materials with potential in adsorption processes. Preliminary analyses showed that macroporous samples obtained with 32 wt% IONPs led to methylene blue (MB) adsorption capacities as high as 400 mg dye/g ferrogel, for dye concentrations as low as 10 mg/L. These results show that the use of an adequate strategy for the processing of macroporous ferrogels can be of high importance in the design of new adsorbents and superabsorbent hydrogels.

Study and optimization of formulation parameters during freeze–drying cycles of model probiotic: Morphology characterization of lyophilisates by scanning electron microscopy

These experimental data are concerning the optimization of freeze-drying cycles of a model-type Casei probiotic bacteria with water based formulations using lactose and polymer polyvinylpyrrolidone (PVP) as cryo-/lyo-protectants. After a previous study devoted to the influence of the main freeze-drying parameters (freezing rates; shelf temperature; absolute pressure) on the bacteria survival ratios, this paper reports some morphological data obtained by scanning electron microscopy (SEM) with the final lyophilisates. The numerous and original SEM images realized with different formulations of water binary or ternary mixtures with fixed operating conditions proved to be very useful to explain and to understand the different bacteria survival ratios observed. Thus, with bacteria or micro-organisms systems, this powerful investigation method of characterization of lyophilisates morphology should be more largely used in the future for setting up the optimal formulations parameters (composition) and the connected operating physical parameters of freeze-drying steps (freezing rate, shelf temperature, absolute pressure).

One 3D aerogel wearable pressure sensor with ultrahigh sensitivity, wide working range, low detection limit for voice recognition and physiological signal monitoring

With the rapid development of intelligent electronic devices, there is a growing demand for wearable pressure sensors with ultrahigh sensitivity, a wide working range, and a low detection limit simultaneously. In this paper, we create a piezoresistive pressure sensor with an ultralight (29.5 mg cm−3) and elastic three-dimensional (3D) chitosan/MXene (CS/MXene) composite aerogel. Because of the strong electrostatic attraction between CS and MXene, CS/MXene aerogels with good mechanical properties can be obtained in a single freeze-drying step with no additional chemical treatment. Furthermore, the abundant amino and carboxyl groups in CS form hydrogen bonds with the −O and −F groups on the surface of MXene, significantly improving the mechanical strength of the composite aerogel. As a result, the CS/MXene composite aerogel sensor has a sensitivity of 709.38 kPa−1 in small pressure region (<1 kPa) and 252.37 kPa−1 in large pressure region (1–20 kPa), which are the highest values reported among the same type of aerogel sensors in the same pressure ranges. Furthermore, the sensor has a fast response time (120 ms), an ultralow detection limit of 1.4 Pa, and good stability (10,000 cycles with almost no fatigue). Because of the improved sensitivity, the competitive aerogel sensor can be used in a voice recognition system that can distinguish between different audio components. It also shows promise in detecting human and animal physiological signals ranging from low to high pressure and mapping spatial pressure distributions.

A highly efficient acetone gas sensor based on 2D porous ZnFe2O4 nanosheets

In this study, 2D porous ZnFe2O4 nanosheets (ZnFe2O4 NSs) were fabricated for use as sensing materials using a 3-stage process involving soaking, freeze-drying, and calcination steps. The ZnFe2O4 NS-based sensor produced exhibited satisfactory sensing performance and selectively for acetone and achieved a response value of 64.9 at 50 ppm and response/recovery times of 23 and 9 s at operating temperature, which was far better than the performances of ZnO NSs and Fe2O3 NSs (controls) produced using the same method. The excellent sensing properties of ZnFe2O4 NSs were attributed to greater porosity, larger pore sizes, and higher proportions of oxygen-deficient and chemisorbed oxygen species. The study shows that the ZnFe2O4 NS-based sensing material produced for the detection of VOCs, especially acetone, shows considerable promise.

One-Step Synthesis of 3D Pore-Structured Adsorbent by Cross-Linked PEI and Graphene Oxide Sheets and Its Application in CO2 Adsorption.

In this study, a one-step method of polyethylenimine (PEI) cross-linking graphene oxide (GO) was used to prepare a 3D pore-structured adsorbent with abundant amine groups for chemisorption of CO2. The cross-linking of PEI with GO sheets and the vacuum freeze-drying step are the keys to the formation of the 3D pore structure. The results of characterization analysis revealed that the as-prepared adsorbent had a 3D porous structure rich in amine groups. Besides, the adsorption/desorption test showed that the prepared adsorbent has excellent and stable adsorption performance, and the maximum CO2 adsorption capacity is 2.18 mmol/g at 343 K and 10 vol % CO2. Moreover, the adsorption kinetics analysis indicated that the adsorption process was dominated by homogeneous adsorption, and the adsorbent had a strong affinity with CO2. Finally, the correlation analysis shows that the kinetic constants obtained by the Avrami model simulation can be effectively used for the actual CO2 adsorption process design.

Spray-drying to improve the functionality of amaranth protein via ultrasonic-assisted Maillard conjugation with red seaweed polysaccharide

Maillard conjugation has gained attention for its application in improving functional-properties of different plant proteins, including solubility and emulsification. Amaranth, a plant protein showing a higher lysine-content essential for conjugation, was conjugated with Gracilaria secundata polysaccharide via ultrasonic-assisted Maillard-conjugation. Post-ultrasonication, the outcomes from spray-drying as an alternative to freeze-drying were investigated. The comparison was based on conjugation-degree, solubility, water-or-oil holding capacity, and secondary structural changes in proteins. The protein: polysaccharide (w/w) of 1:1 and 2:1 displayed better conjugation, improved functional and structural aspects including the changes in the amide regions, oil-and-water holding capacity of the protein. Lower degree of conjugation, structural and functional changes for 1:2 samples can be the result of higher polysaccharide content leading to a shielding-effect over the reaction terminals of proteins. A significant difference between the properties was observed with different drying methods. Except for similar conjugation efficiency, the freeze-dried samples exhibited better oil-holding capacity, while the spray-dried samples performed better in water-holding capacity. The difference between spray-drying and freeze-drying could be due to the temperature difference resulting in protein denaturation, or the advancement of Maillard reaction. We demonstrated that spray-drying could be utilized as an alternative to freeze-drying step during ultrasonic-assisted Maillard conjugation, although a focus on optimization of conjugation and spray-drying parameters is required.

Agarose Gel-Templating Synthesis of a 3D Wrinkled Graphene Architecture for Enhanced Supercapacitor Performance.

The increasing use of rapidly fluctuating renewable energy sources, such as sunlight, has necessitated the use of supercapacitors, which are a type of energy storage system with high power. Chemically exfoliated graphene oxide (GO) is a representative starting material in the fabrication of supercapacitor electrodes based on reduced GO (rGO). However, the restacking of rGO sheets driven by π–π stacking interactions leads to a significant decrease in the electrochemically active surface area, leading to a loss of energy density. Here, to effectively inhibit restacking and construct a three-dimensional wrinkled structure of rGO (3DWG), we propose an agarose gel-templating method that uses agarose gel as a soft and removable template. The 3DWG, prepared via the sequential steps of gelation, freeze-drying, and calcination, exhibits a macroporous 3D structure and 5.5-fold higher specific capacitance than that of rGO restacked without the agarose template. Further, we demonstrate a “gel-stamping” method to fabricate thin-line patterned 3DWG, which involves the gelation of the GO–agarose gel within micrometer-sized channels of a customized polydimethylsiloxane (PDMS) mold. As an easy and low-cost manufacturing process, the proposed agarose gel templating method could provide a promising strategy for the 3D structuring of rGO.

Low-cost sample preservation methods for high-throughput processing of rumen microbiomes

BackgroundThe use of rumen microbial community (RMC) profiles to predict methane emissions has driven interest in ruminal DNA preservation and extraction protocols that can be processed cheaply while also maintaining or improving DNA quality for RMC profiling. Our standard approach for preserving rumen samples, as defined in the Global Rumen Census (GRC), requires time-consuming pre-processing steps of freeze drying and grinding prior to international transportation and DNA extraction. This impedes researchers unable to access sufficient funding or infrastructure. To circumvent these pre-processing steps, we investigated three methods of preserving rumen samples for subsequent DNA extraction, based on existing lysis buffers Tris-NaCl-EDTA-SDS (TNx2) and guanidine hydrochloride (GHx2), or 100% ethanol.ResultsRumen samples were collected via stomach intubation from 151 sheep at two time-points 2 weeks apart. Each sample was separated into four subsamples and preserved using the three preservation methods and the GRC method (n = 4 × 302). DNA was extracted and sequenced using Restriction Enzyme-Reduced Representation Sequencing to generate RMC profiles. Differences in DNA yield, quality and integrity, and sequencing metrics were observed across the methods (p < 0.0001). Ethanol exhibited poorer quality DNA (A260/A230 < 2) and more failed samples compared to the other methods. Samples preserved using the GRC method had smaller relative abundances in gram-negative genera Anaerovibrio, Bacteroides, Prevotella, Selenomonas, and Succiniclasticum, but larger relative abundances in the majority of 56 additional genera compared to TNx2 and GHx2. However, log10 relative abundances across all genera and time-points for TNx2 and GHx2 were on average consistent (R2 > 0.99) but slightly more variable compared to the GRC method. Relative abundances were moderately to highly correlated (0.68 ± 0.13) between methods for samples collected within a time-point, which was greater than the average correlation (0.17 ± 0.11) between time-points within a preservation method.ConclusionsThe two modified lysis buffers solutions (TNx2 and GHx2) proposed in this study were shown to be viable alternatives to the GRC method for RMC profiling in sheep. Use of these preservative solutions reduces cost and improves throughput associated with processing and sequencing ruminal samples. This development could significantly advance implementation of RMC profiles as a tool for breeding ruminant livestock.

Efficacy of sugar excipients on lyophilized C22 phage infectivity evaluated by atomic force microscopy

Bacteriophages (phages) show immense potential as biological control agents of pathogenic bacteria in crops. However, their utilization is hindered by the challenges in storage and handling in remote farming areas. Lyophilization has been used to convert phages from solution to powdery form to overcome such issues. In this work, we lyophilized the C22 phage, a promising biocontrol agent of Ralstonia solanacearum causing wilt disease. Sugar excipients were added during the lyophilization step to preserve phage infectivity. We found that 0.5 M sucrose, 0.25 M, and 0.5 M trehalose could retain infectivity of lyophilized C22 phage for ≥ 45% after 90–day storage. Using atomic force microscopy-based imaging, we revealed that both sugars induced aggregation of C22 phage particles. We suggest that aggregation may be a mechanism that prevents phage from degradation since it reduces overall surface that can unfavorably interact with external damaging factors. An insight into phage aggregation can be essential for phage storage and utilization in biocontrol applications.

Porous soluble dialdehyde cellulose beads: A new carrier for the formulation of poorly water-soluble drugs

Cellulose beads are porous spherical particles with promising futures for drug delivery applications. In this study, novel dialdehyde cellulose (DAC) beads are developed by periodate oxidation of pristine cellulose for oral delivery of weakly basic poorly water-soluble drugs. Diazepam and itraconazole were studied as model drugs. Drug loadings in DAC beads up to 40% were obtained. Depending on the drug loading, complete or partial amorphization of drugs in DAC beads was observed. Drugs in the amorphous state not only presented a higher extent of dissolution from the DAC beads compared to the crystalline model drug, but the obtained concentration was also supersaturated. This supersaturation is attributed to the amorphization of the drugs in the beads in conjunction with the dissolution of the DAC beads at a neutral pH of the dissolution medium. Further, the effects of two different solvent systems used in the lyophilization step during the preparation of the DAC beads (100% water and 90/10% tert-butanol/water mixture) on their structure were investigated. Interestingly, the selection of the solvent system greatly impacted the bead structure, resulting in radically different drug loading capacity, physical properties, and release behavior of the model drugs. In summary, this is the first study that reports on exploiting soluble, porous, dialdehyde cellulose beads, showing great potential as a carrier for improving the rate and extent of dissolution of poorly soluble drugs and maintaining supersaturation.

Impact of the Purification Process on the Spray-Drying Performances of the Three Families of Lipopeptide Biosurfactant Produced by Bacillus subtilis.

Lipopeptides produced by Bacillus subtilis display many activities (surfactant, antimicrobial, and antitumoral), which make them interesting compounds with a wide range of applications. During the past years, several processes have been developed to enable their production and purification with suitable yield and purity. The already implemented processes mainly end with a critical drying step, which is currently achieved by freeze-drying. In this study, the possibility to replace this freeze-drying step with a spray-drying one, more suited to industrial applications, was analyzed. After evaluating their thermal resistance, we have developed a spray-drying methodology applicable for the three lipopeptides families produced by B. subtilis, i.e., surfactin, mycosubtilin (iturin family), and plipastatin (fengycin family). For each lipopeptide, the spray-drying procedure was applied at three steps of the purification process by ultrafiltration (supernatant, diafiltered solution, and pre-purified fraction). The analysis of the activities of each spray-dried lipopeptide showed that this drying method is not decreasing its antimicrobial and biosurfactant properties. The methodology developed in this study enabled for the first time the spray-drying of surfactin, without adjuvants’ addition and regardless of the purification step considered. In the case of fengycin and mycosubtilin, only diafiltered solution and purified fraction could be successfully spray-dried without the addition of adjuvant. Maltodextrin addition was also investigated as the solution for the direct drying of supernatant. As expected, the performances of the spray-drying step and the purity of the powder obtained are highly related to the purification step at which the product was dried. Interestingly, the impact of mycosubtilin concentration on spray-drying yield was also evidenced.