A novel set-up and a CFD approach to study the biofilm dynamics as a function of local flow conditions encountered in fresh-cut food processing equipments

The hydrodynamic conditions as well as design and surface properties within fresh-cut food processing equipment create a complex environment for biofilms. A new experimental approach was thus proposed to identify those physical parameters impacting biofilm development in such conditions. A set-up comprising original mock-ups mimicking generic features of washing tanks (e.g. welds, folds, flat surfaces, air/liquid/wall interface) was designed. The flow pattern therein was characterized using two computational fluid dynamic calculation approaches. Full trials were run for 48 h at 10 °C with a Pseudomonas fluorescens strain to identify the preferential biofilm formation areas. As in current industrial systems, the pilot rig had recirculation areas and low wall shear stress rates (τ_w < 0.1 Pa) in corners and angles. These were identified as critical areas with Surface Microbial Loads (SML) over 5 Log₁₀/cm². However, τ_w alone failed to explain why SML in areas under unidirectional flow was higher than in the mock-ups. Lastly, air/liquid/wall interface conditions were more critical than immersed surfaces. This study validated the possibility of using CFD methods to understand the way in which flow pattern influences biofilm formation. The methodology proposed would be helpful in quantifying equipment components criticality based on biofilm growth parameters.     

CO2 laser peeling of Al2O3 ceramic and an application for the polishing of laser cut surfaces

A laser controlled fracture peeling technique is demonstrated to smooth the Al₂O₃ ceramic surface without thermal damages. It was found that a chip can be separated and curled from the ceramic surface during a focused CO₂ continuous wave (CW) laser dual-scanning. The thickness of the curled chip is ～50 μm and the formed subsurface roughness (R_a ≈ 2 μm) is close to the surface machined by mechanical breaking (R_a = 1.84 μm). The chip formation is attributed to the controlled fracture by the residual tensile stress in the recast layer, whereas the chip curling only occurs when the melting depth is shallower than the position of lateral cracks. The peeling technique can be applied to polish the cut surface of laser fusion cutting in ceramics. The polished cut surface (R_a = 2.18 μm) is free from recast, crack and heat effects. The microstructure is similar to the base material. The material removal rate during polishing is up to 0.125 mm³/s.     

In vitro Streptococcus mutans biofilm formation on surfaces of chlorhexidine-containing dentin bonding systems

This in vitro study evaluated the influence of chlorhexidine diacetate (CDA) when blended within dentin bonding systems (DBSs) on Streptococcus mutans (S. mutans) biofilm formation.One commercially available 0.2% wt CDA-containing DBS (Peak Universal Bond) and five experimental 0.2% wt CDA-containing DBS formulations (experimental Adper Scotchbond 1XT plus experimental resins, R₂, R₃, R₄, R₅) were assessed vs their no-CDA containing counterparts. Twenty-eight DBSs disks were prepared for each group (6.4 mm×1.0 mm) and cured for 80 s at 800 mW/cm² in a nitrogen atmosphere. A modified Drip-Flow Reactor was used to grow S. mutans biofilms on specimen surfaces for 24 h and adherent, viable biomass was evaluated using a tetrazolium salt assay (MTT). Two specimens from each of the tested materials were processed with LIVE/DEAD stain and observed using laser confocal microscopy (CLSM) while two disks from each group were examined by using scanning electron microscopy (SEM).MTT assay, CLSM and SEM observations showed that CDA addition decreased, increased or did not change S. mutans biofilm formation. The lowest biofilm formation was obtained with Peak Universal Bond and R₅ (with and without CDA).It may be concluded that the chemical composition of DBSs determines their ability to promote or hamper biofilm formation. Therefore, CDA addition may be helpful in modulating biofilm formation provided that DBS formulation is tuned and optimized.     

Phase equilibria of (CO2 + H2O + NaCl) and (CO2 + H2O + KCl): Measurements and modeling

We report experimental measurements of the phase behavior of (CO₂ + H₂O + NaCl) and (CO₂ + H₂O + KCl) at temperatures from 323.15 K to 423.15 K, pressure up to 18.0 MPa, and molalities of 2.5 and 4.0 mol kg⁻¹. The present study was made using an analytical apparatus and is the first in which coexisting vapor- and liquid-phase composition data are provided. The new measurements are compared with the available literature data for the solubility of CO₂ in brines, many of which were measured with the synthetic method. Some literature data show large deviations from our results.The asymmetric (γ–φ) approach is used to model the phase behavior of the two systems, with the Peng–Robinson equation of state to describe the vapor phase, and the electrolyte NRTL solution model to describe the liquid phase. The model describes the mixtures in a way that preserves from our previous work on (CO₂ + H₂O) the values of the Henry's law constant and the partial molar volume of CO₂ at infinite dilution Hou et al. [22]. The activity coefficients of CO₂ in the aqueous phase are provided. Additionally, the correlation of Duan et al. [14] for the solubility of CO₂ in brines is tested against our liquid-phase data.     

Combined high hydrostatic pressure and carbon dioxide inactivation of pectin methylesterase,polyphenol oxidase and peroxidase in feijoa puree

A combined treatment of high hydrostatic pressure (HHP) and dense phase carbon dioxide (DPCD) was investigated to inactivate pectin methylesterase (PME), peroxidase (POD) and polyphenol oxidase (PPO) in feijoa (Acca sellowiana) puree. The treatments were HHP (HHP); carbonation and HHP (HHPcarb); carbonation + addition of 8.5 mL CO₂/g puree into the headspace of the package and HHP (HHPcarb + CO₂). The different samples were treated at 300, 450 and 600 MPa, for 5 min.The residual POD and PPO activity decreased in the order HHP > HHPcarb > HHPcarb + CO₂ at all pressures used. Treatments with HHP at 300 MPa increased POD activity to 140%. The residual PME activity of HHPcarb and HHPcarb + CO₂ samples at 600 MPa (45–50%) was significantly (p < 0.05) lower than for HHP treatment (65%).The simultaneous application of HHP and DPCD seems to synergistically enhance the inactivation of the enzymes studied, the CO₂ concentration being a key process factor.     

Synthesis of a biocompatible polymer using siloxane-based surfactants in supercritical carbon dioxide

Poly(N-vinyl-2-pyrrolidone) (PVP) particles were prepared by dispersion polymerization in the presence of 2,2′-azobisisobutyronitrile as the initiator and siloxane-based surfactant in supercritical carbon dioxide (scCO₂). The dispersants used in this study were non-ionic, non-reactive and commercially produced siloxane-based surfactants (Monasil PCA and KF-6017). We investigated the effect of kinds and concentrations of the surfactants, in addition to the reaction temperature and the concentration of the monomer on the particle size and morphology. PVP microspheres were prepared in 0.23–0.74 μm size range with Monasil PCA and 0.71–1.98 μm size range with KF-6017, respectively. The resulting polymer particle of >90% yield was obtained. Particle size slightly increased with the amount of monomer in polymerization with Monasil PCA. In the case of KF-6017 as the surfactant, there was not an obvious variation in particle size with increasing monomer. Particle size of PVP decreased as surfactant concentration increased from 5.0 to 15.0 wt.% basis on concentration of monomer. The narrow particle size distribution (D_n = 0.23 μm and PSD = 1.06) was presented at the high concentration of Monasil PCA (15 wt.% on monomer concentration). As indicated by the reaction temperature and the addition of organic solvent, which affected solubility of monomer, polymer and surfactant in scCO₂, particle size and particle size distribution of PVP varied. PVP particles with Monasil PCA strongly aggregated at 75 °C in contrast to KF-6017 which showed discrete particles at 65 and 70 °C, but particle size distribution was broad. Particle size was slightly reduced with a little amount of hexane, with an inverse relationship of adding hexane reduced the particle size. The amount of the relative residual surfactants on surface of the polymer after extracting with supercritical fluid process (SFE) was measured by using SEM/EDS and EPMA analysis to map out the distribution of silicon element qualitatively. The original polymer particle before the extraction using CO₂ had the high level of silicon element, but the average level of silicon element became low after CO₂ extraction.     

Bubble point pressures and densities of hexamethyldisiloxane–carbon dioxide binary mixture using a constant volume view cell

The phase behavior of hexamethyldisiloxane (HMDS)–carbon dioxide (CO₂) binary mixture was investigated using a constant volume view cell. The accuracy of the measurement technique was inspected against the bubble point pressure data in the literature for ethanol (C₂H₅OH)–carbon dioxide (CO₂) binary mixture. The bubble point pressures for C₂H₅OH–CO₂ agreed well with the literature values. The bubble point pressures of HMDS–CO₂ binary mixture were determined at five different temperatures (T = 298.2 K, 308.2 K, 313.2 K, 323.2 K, 333.2 K) and at various compositions. The bubble point pressures increased with increasing temperature and CO₂ mole fraction in the binary mixture. The phase behavior of the binary mixture was modeled using the Peng–Robinson Stryjek–Vera equation of state (PRSVEoS). The binary interaction parameters were regressed from experimental bubble point pressures at each temperature and were found to exhibit a linear dependency on temperature. The HMDS–CO₂ binary mixture was also found to exhibit Type II phase behavior. Additionally, P–T–ρ measurements for the same binary system were conducted and excess molar volumes were calculated.     

In situ FTIR micro-spectroscopy to investigate polymeric fibers under supercritical carbon dioxide: CO2 sorption and swelling measurements

An original experimental set-up combining a FTIR (Fourier Transformed InfraRed) microscope with a high pressure cell has been built in order to analyze in situ and simultaneously the CO₂ sorption and the polymer swelling of microscopic polymer samples, such as fibers, subjected to supercritical carbon dioxide. Thanks to this experimental set-up, we have determined as a function of the CO₂ pressure (from 2 to 15 MPa) the CO₂ sorption and the polymer swelling at T = 40 °C of four polymer samples, namely PEO (polyethylene oxide), PLLA (poly-l-lactide acid), PET (polyethylene terephtalate) and PP (polypropylene). The quantity of CO₂ sorbed in all the studied polymers increases with pressure. PEO and PLLA display a significant level of CO₂ sorption (20 and 25% respectively, at P = 15 MPa). However, we observe that a lower quantity of CO₂ can be sorbed into PP and PET (7 and 8% respectively, at P = 15 MPa). Comparing their thermodynamic behaviors and their intrinsic properties, we emphasize that a high CO₂ sorption can be reach if on one hand, the polymer is able to form specific interaction with CO₂ in order to thermodynamically favor the presence of CO₂ molecules inside the polymer and on the other, displays high chains mobility in the amorphous region. PLLA and PEO fulfilled these two requirements whereas only one property is fulfilled by PET (specific interaction with CO₂) and PP (high chains mobility). Finally, we have found that for a given CO₂ sorption, the resulting swelling of the polymer depends mainly on its crystallinity.     

Supercritical CO2 extraction of lutein esters from marigold (Tagetes erecta L.) enhanced by ultrasound

As a novel technique, supercritical CO₂ (SC-CO₂) extraction enhanced by ultrasound was applied to the extraction of lutein esters from marigold and the extraction curves were described by Sovová model. The mass transfer coefficient in the solid phase (k_s) increased from 3.1 × 10⁻⁹ to 4.3 × 10⁻⁹ m/s due to ultrasound. The effect of extraction parameters including particle size of matrix, temperature, pressure, flow rate of CO₂, and ultrasonic conditions consisting of power, frequency and irradiation time/interval on the yield of lutein esters were investigated with single factor experiments. The results showed that the yield of lutein esters increased significantly with the presence of ultrasound (p < 0.05). The maximal yield of lutein esters (690 mg/100 g) was obtained for a particle size fraction of 0.245–0.350 mm, extraction pressure of 32.5 MPa, temperature of 55 °C and CO₂ flow rate of 10 kg/h with ultrasonic power of 400 W, ultrasonic frequency of 25 kHz and ultrasonic irradiation time/interval of 6/9 s.     

Ovicidal activities of supercritical CO2 and N2O on Ascaris suum eggs

This study examined whether supercritical CO₂ and N₂O fluids are effective in inactivating Ascaris suum eggs, which were chosen as a model for parasite eggs. The treatments were carried out in a multibatch apparatus, in which, the eggs could be placed atop a solid surface (non-immersed condition) or in aqueous solution (immersed condition). Various CO₂ and N₂O phases—including gas (6 MPa, 30 °C), liquid (8 MPa, 30 °C), subcritical (10 MPa, 30 °C), and supercritical (10 MPa, 37 °C)—were tested with exposure times ranging from 1 to 20 min. Supercritical CO₂ and N₂O both showed a similar, strong ovicidal effect, requiring only 1 min in non-immersed conditions and 5 min in water-immersed conditions to achieve a 2.4-log inactivation. Subcritical CO₂ and N₂O showed a weaker ovicidal effect. The effect was significantly reduced for the gas and liquid phases, compared with the supercritical phases. This study reports that supercritical CO₂ and N₂O can be effectively employed as a non-thermal treatment technique to control parasite egg contamination in fecal matter and food.     

Comparison of the rate of CO2 absorption into aqueous ammonia and monoethanolamine

Aqueous ammonia has been proposed as an absorbent for use in CO₂ post combustion capture applications. It has a number of advantages over MEA such as high absorption capacity, low energy requirements for CO₂ regeneration and resistance to oxidative and thermal degradation. However, due to its small molecular weight and large vapour pressure absorption must be carried at low temperature to minimise ammonia loss. In this work the rate of CO₂ absorption into a falling thin film has been measured using a wetted-wall column for aqueous ammonia between 0.6 and 6 mol L^?1, 278–293 K and 0–0.8 liquid CO₂ loading. The results were compared to 5 mol L^?1 MEA at 303 and 313 K. It was found that the overall mass transfer coefficient for aqueous ammonia was at least 1.5–2 times smaller than MEA at the measured temperatures. From determination of the second-order reaction rate constant k₂ (915 L mol^?1 s^?1 at 283 K) and activation energy E_a (61 kJ mol^?1) it was shown that the difference in mass transfer rate is likely due to both the reduced temperature and differences in reactivity between ammonia and MEA with CO₂.     

Oxygen at the interface of CVD diamond films on silicon

The oxygen incorporation at the interface between the silicon substrate and chemical vapour deposited (CVD) diamond films nucleated by the bias-enhanced nucleation (BEN) procedure has been studied by heavy-ion elastic recoil detection (ERD). Using standard process conditions for the realisation of heteroepitaxial films, oxygen with a concentration equivalent to about 1 nm SiO₂ has been found, which was mainly incorporated during textured growth with a certain CO₂ admixture to the process gas. By completely omitting CO₂ during nucleation and growth, the oxygen at the interface can be reduced by nearly one order of magnitude to 6.3×10¹⁵ at cm⁻², corresponding to 0.14 nm SiO₂. Intentional addition of highly enriched C¹⁸O₂ to the gas phase shows that the oxygen incorporation is strongly enhanced during BEN with hydrocarbon in the gas phase. The results indicate that roughening of the surface, the deposition of Si_xO_yC_z phases and strong lateral inhomogeneities at the silicon interface may explain the coexistence of epitaxial crystallites and amorphous phases. It is suggested that a further reduction of the oxygen concentration at the interface may have consequences for an improved heteroepitaxy of diamond on silicon.     

Near-infrared spectroscopic solubility measurement for thermodynamic analysis of melting point depressions of biphenyl and naphthalene under high-pressure CO2

Melting temperatures of organic solids are often depressed by high-pressure CO₂ due to a dissolution of CO₂ in the molten organic compounds. For thermodynamic analysis of the melting point depression, solubilities of CO₂ in molten biphenyl and naphthalene were measured by near-infrared spectroscopy at various temperatures and pressures up to 20 MPa. Molarity of the organic component was determined from the 3ν_CH absorption band, and that of CO₂ from the 2ν₁ + ν₃ band. Mole fraction of CO₂ in the liquid phase was found to be an increasing function of the pressure up to 0.6 at 20 MPa and a weakly decreasing function of the temperature. The solubility data were used for modeling of the mixtures by the Peng–Robinson equation of state with a binary interaction parameter k₁₂. Calculation of the solid–liquid–gas phase equilibrium for the model fluid qualitatively described a large decrease in the melting temperature with increasing pressure up to 10 MPa followed by a small change at higher pressures. The melting point change was interpreted by the two competing effects: hydrostatic pressure effect increases the melting point by ca. 8 °C at 20 MPa, whereas CO₂ solubility effect reduces it by ca. 30 °C. Decomposition of the solubility effect into ideal and non-ideal mixing parts revealed that the non-ideality increases the melting point by more than 10 °C.     

Extraction of sunflower oil with supercritical CO2: Experiments and modeling

Extraction of sunflower oil from sunflower seeds (Heliantus annuus L.) using supercritical CO₂ was studied. The shrinking core model was applied to the modeling of the packed-bed extraction process. The experimental data were obtained for extraction conducted at the pressures of 20, 30, 40, 50 and 60 MPa; the temperatures of 313, 333 and 353 K, the CO₂ flow rates of 1–4, and 6 cm³ CO₂ min⁻¹; the mean particle diameters of 0.23, 0.55, 1.09, 2.18 mm. The supercritical CO₂ extraction process was modeled by a quasi steady state model as a function of extraction time, pressure, temperature, CO₂ flow rate, and particle diameter. The supercritical CO₂ extraction process. The intraparticle diffusion coefficient (effective diffusivity) D_e was used as adjustable parameter. The model using the best fit of D_e was correlated the data satisfactorily.     

Measurements of the flow of supercritical carbon dioxide through short orifices

This paper describes the methods used to measure flow rate of supercritical and two-phase CO₂ through short orifices. Orifices with diameters of 1 millimeter and orifice length-to-diameter ratios of 3.2 and 5 were tested. Flow rates through these orifices were measured over a broad range of inlet conditions in the supercritical region with orifice inlet pressures ranging from 5 MPa to 11 MPa and inlet densities ranging from 86.5 kg/m³ to 630 kg/m³. The data were compared to the isentropic real gas model for expansion of a fluid through a nozzle in order to observe the behavior of the discharge coefficient. For a given orifice inlet condition, the single-phase discharge coefficient was found to be between 0.81 and 0.87 and was independent of the pressure ratio. The discharge coefficient increased as the pressure ratio decreased when two-phase CO₂ was present with orifice inlet pressures of 7.7 MPa and 9 MPa. The critical mass flow rate and critical pressure ratio were determined for each test. The raw data from this investigation are available on the internet.This paper describes the methods used to measure flow of supercritical and two-phase CO₂ through short orifices. Orifices with diameters of 1 millimeter and orifice length-to-diameter ratios of 3.2 and 5 were tested. Flow rates through these orifices were measured over a broad range of inlet conditions in the supercritical region with orifice inlet pressures ranging from 7.7 MPa to 11 MPa and inlet densities ranging from 111 kg/m³ to 630 kg/m³. The data were compared to the isentropic real gas model for expansion of a fluid through a nozzle in order to observe the behavior of the discharge coefficient. For a given orifice inlet condition, the single-phase discharge coefficient was found to be between 0.81 and 0.87 and was independent of the pressure ratio. The discharge coefficient increased as the pressure ratio decreased when two-phase CO² was present with orifice inlet pressures of 7.7 MPa and 9 MPa. The critical mass flow rate and critical pressure ratio were determined for each test. The raw data from this investigation are available on the internet.     

Phase equilibria of the propylene glycol/CO2 and propylene glycol/ethanol/CO2 systems

The high-pressure vapour–liquid phase equilibria (P–T–x–y) of the binary mixture propylene glycol/CO₂ have been experimentally investigated at temperatures of (398.2, 423.2 and 453.2) K over the pressure range from (2.5 to 55.0) MPa using a static-analytic method. Furthermore, the high-pressure vapour–liquid phase equilibria (P–T–x–y) of the ternary mixture propylene glycol/CO₂/ethanol at constant temperatures of (398.2, 423.2 and 453.2) K and at constant pressure of 15.0 MPa have been determined using a static-analytic method. Initial concentrations of components in propylene glycol (PG)/ethanol (EtOH) mixture vary from 10 up to 90 wt.%. In general, for binary system it was observed that the solubility of CO₂ in the heavy propylene glycol reach phase increases with increasing pressure at constant temperature. On the contrary, the composition of gaseous phase is not influenced by the pressure or the temperature. On average the solubility of PG in light phase of CO₂ amounts to 30 wt.%. The system behaviour at temperature of 398.2 K was investigated up to 70.0 MPa and a single-phase region was not observed. Above the pressure 60.0 MPa a single-phase region of the system was observed for the temperature of 423.2 K. For the temperature of 453.2 K the single-phase was observed above the pressure of 48.0 MPa. For ternary system it was observed that the composition of heavy phase is slightly influenced by the temperature when the mass fraction of EtOH in initial mixture is higher than 50 wt.%. If the mass fraction of PG in initial mixture is higher than 50 wt.%, the composition of heavy phase is not influenced by the temperature anymore. The composition of the PG, EtOH and CO₂ in light phase remains more or less unchanged and it is not influenced by the conditions.     

Fructooligosacharides production in aqueous medium with inulinase from Aspergillus niger and Kluyveromyces marxianus NRRL Y-7571 immobilized and treated in pressurized CO2

This work investigated the influence of compressed CO₂ treatment on the enzymatic activity of immobilized inulinases, and the production of fructooligosacharides in aqueous medium using these enzymes. The effects of system pressure, exposure time and depressurization rate on the enzymatic activity were evaluated through central composite designs (CCD) 2³. Inulinase from Kluyveromyces marxianus NRRL Y-7571 presented an increase of 104% in the residual activity using CO₂ at 275 bar submitted to 6 h treatment, at a depressurization rate of 10 kg m^?3 min^?1. For Aspergillus niger commercial inulinase, a decrease in enzyme activity was observed (residual activity of 39%) using CO₂ treatment at 75 bar for 6 h exposure at the highest depressurization rate (200 kg m^?3 min^?1). Enzymatic activities changed significantly depending on the enzyme source and the experimental treatment conditions investigated. The values of FOS obtained using inulinases from A. niger were 30.64% of GF2; 13.90% of GF3 and 2.88% of GF4 in the medium containing inulin as substrate. Results demonstrate that the use of compressed CO₂ might be of technological importance as a preceding, preparation step, to improve enzyme activity, hence helping the development of new biotransformation processes.     

Solubility and diffusion coefficient of supercritical-CO2 in polycarbonate and CO2 induced crystallization of polycarbonate

The solubility and diffusion coefficient of supercritical CO₂ in polycarbonate (PC) were measured using a magnetic suspension balance at sorption temperatures that ranged from 75 to 175 °C and at sorption pressures as high as 20 MPa. Above certain threshold pressures, the solubility of CO₂ decreased with time after showing a maximum value at a constant sorption temperature and pressure. This phenomenon indicated the crystallization of PC due to the plasticization effect of dissolved CO₂. A thorough investigation into the dependence of sorption temperature and pressure on the crystallinity of PC showed that the crystallization of PC occurred when the difference between the sorption temperature and the depressed glass transition temperature exceeded 40 °C (T − T_g ≥ 40 °C). Furthermore, the crystallization rate of PC was determined according to Avrami's equation. The crystallization rate increased with the sorption pressure and was at its maximum at a certain temperature under a constant pressure.     

Enrichment of docosahexaenoic acid from tuna oil via lipase-mediated esterification under pressurized carbon dioxide

This study focused on the use of pressurized CO₂ as a reaction medium for the enrichment of docosahexaenoic acid (DHA) from tuna oil fatty acids via lipase-mediated esterification. Of the three lipases tested, Lipozyme RM IM from Rhizomucor miehei was selected for further study. Enzyme loading, water addition, and reaction time were also explored. Near-supercritical CO₂, prepared at 25 °C and 8.3 MPa, was the most effective reagent tested for enriching DHA from the residual fatty acid fraction. In addition to near-supercritical CO₂, optimal conditions included addition of 0.2 wt% (based on total substrates) water, enzyme loading of 5 wt% (based on total substrates), and a reaction time of 18 h. The DHA concentration and recovery yield for the residual fatty acid fraction under these optimal conditions were 75.8 wt% and 81 wt%, respectively.     

Methanol synthesis over binary copper-f block element intermetallic compounds

LnCu₂ (Ln = La, Ce, Gd, Tm) binary copper-f block element intermetallic compounds were tested as catalysts for the production of methanol using greenhouse gases (CO₂ and CH₄) as feedstock. The best results were obtained with PrCu₂ and LaCu₂, which are more active for the production of methanol than a commercial Cu based catalyst (Alfa Aesar, 45776-0500) using CO₂ + H₂ (1:3) or CH₄ + CO₂ + H₂ (1:1:3) in the feed composition. The selectivity is also very high (> 80%), but the incorporation of CH₄ to the feedstock has a negative effect on the catalyst's behavior. LnCu₂ also present a remarkable long term stability for at least 50 h on the gaseous stream. To our knowledge, the results herein described are among the best reported until now.