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International audience; This study elucidates the effect of colony formation on light absorption by Botryococcus braunii microalgae cells. The spectral average mass absorption cross-section of suspensions of B. braunii cultures with free-floating cells or colonies was measured experimentally across the photosynthetically active radiation region. The average mass absorption cross-section was found to decrease significantly across the spectrum in the presence of colonies. This observation could be attributed to (i) reduced pigment concentrations due to nutrient limitations, (ii) mutual shading of the aggregated cells, and/or (iii) the presence of the colonies' extracellular matrix. The Monte Carlo ray tracing method was used to elucidate the contribution of each of these phenomena on the mass absorption cross-section of cells in colonies. Colonies were modeled either as fractal aggregates of monodisperse cells or as an ensemble of monodisperse cells regularly arranged at the periphery of a hollow sphere embedded in a spherical extracellular matrix or as a volume and average projected area equivalent coated sphere. The change in pigment concentrations due to nutrient limitation was found to be the most important factor. In addition, the mass absorption cross-section of cells in colonies was found to decrease due to mutual shading among cells. This effect was stronger with increasing number of cells in the colony and increasing cell absorption index. The effect of extracellular matrix on the mass absorption cross-section was found to be negligible. Finally, good agreement was found between the equivalent coated sphere approximation and the colonies modeled as fractal aggregates comprised of monodisperse cells. This study also established that the Monte Carlo ray tracing method can be used for a variety of microalgae species and colony configurations, whose absorption cross-section are not readily calculated by standard methods due to their complex geometry, inhomogeneous nature, and large size compared to the wavelength of the incident light.

International audience; Microalgae represent a new source of biomass for many applications. The advantage of microalgae over higher plants is their high productivities. The photoautotrophic microalgae include all photosynthetic microorganisms, i.e. Cyanobacteria (prokaryotes) or microalgae (eukaryotes). These microorganisms are characterized by a large biodiversity and chimiodiversity. Then, the analysis of microalgal and cyanobacterial biomass often needs specific adaptations of the classical protocols for extraction as well as for quantification of their contents. This chapter reviewed the main analytical methods used for the analysis of microalgae biomass and its main vaporizable compounds: proteins, polysaccharides, lipids, pigments and secondary metabolites.

In this paper we present the reactive extrusion process as a method of lipids extraction from by-products of fish. The study focuses on two essential points which are by-product enzymatic hydrolysis efficiency of three fish types, and the technical feasibility of producing a biodiesel from the fish lipids. The parameters of extrusion process were optimized in order to extract the more important percentage of oil. The results of the extracted oil from the three fish types were compared with other techniques such as batch process. Following the enzymatic hydrolysis, the chemical composition and the total fatty acids percentage are determined for each fish oil types in order to select the suitable oil for biodiesel production. Then the selected oil goes through transesterification, and we recover the methyl esters. The results of this study show that the enzymatic hydrolysis of the fish by-products by using the reactive extrusion process is interesting. Moreover, the valorization of fish by-products allows the marine waste recycling while producing biofuel. The produced biofuel can be used as an additive in a diesel fuel.

Botryococcus braunii Bot-22, a hydrocarbon rich microalga known as a potential source of jet fuel, was photoautotrophically grown in a beveled shape flat-panel photobioreactor in continuous cultures. Two photon flux densities (PFD) 50 and 500 μmol photons m−2 s−1, two dilution rates, 0.178 and 0.357 d−1 and two different inlet oxygen concentrations were applied to find suitable conditions for biodiesel production by B. braunii. The main fatty acids detected by GC-FID, were oleic acid, palmitic acid, α-linolenic acid, erucic acid and stearic acid. By doubling the dilution rate from 0.178 to 0.357 d−1 at 500 μmol photons m−2 s−1 light intensity, the PUFAs decreased from 17.65% to 9.98%. In lower dilution rate, the sum of suitable fatty acids percentage for biodiesel known as oleic, palmitic, stearic, and linoleic acids was higher than all other conditions. In cell density lower than 6 g L−1, C16 and C18 fatty acids constituted main composition of microalgae oil content. The maximum productivity of suitable fatty acids for biodiesel mentioned above, all together, was achieved at higher dilution rate, 21% of inlet oxygen concentration and higher light intensity while the highest hydrocarbon productivity achieved at higher dilution rate, higher light intensity and 4% of inlet oxygen concentration.

International audience; This study aims to investigate the triacylglycerol (TAG) productivity of Parachlorella kessleri grown under continuous illumination and to investigate its metabolism in simulated day/night cycles in order to estimate the feasibility of a large-scale production in outdoor solar photobioreactors. The strain was chosen for its ability to accumulate large amounts of triacylglycerol during nitrogen starvation. Several protocols of nitrogen starvation were tested in continuous illumination as well as in simulated day/night cycles. Sudden and progressive nitrogen starvation conditions have enhanced the TAG concentration and productivity of P. kessleri reaching up to 48 dry wt% and 4.4 × 10 −3 kg m −2 day −1 , respectively. Microalgal cell metabolism was significantly affected by the day/night illumination cycles. The energy-rich compounds (TAGs and carbohydrates) were accumulated by P. kessleri during the photope-riods and partly consumed during the dark to sustain the microalgae vitality. This TAG oxidation ultimately led to a 26% decrease in TAG productivity in cultures exposed to day/night cycles compared to ones exposed to continuous illumination of equal 24-h average photon flux density. The results can dictate the optimal time for harvesting cells for recovering the largest amount of TAGs.

The importance of date palm (Phoenix dactylifera L.) deposit could represent an interesting solution for sustainable and integrated energy valorization in Algerian oasis ecosystem. The objective of this work is to study the thermal behavior, under an oxidative atmosphere of the phoenicicole biomass main constituents related to the dominant cultivar, Deglet Nour. Thermogravimetric analysis is the approach used to study the pyrolysis behavior of this lignocellulosic biomass by the determination of the kinetic constant (activation energy, order of the reaction, pre-exponential factor) and the description of different thermal profiles. The results show that combustion process could be an interesting alternative energy recovery for the phoenicicole biomass. This is explained by the low activation energy which is estimated at an average of 29.06 k J/mol and the low residues generated by the thermoconversion. Furthermore, two types of phoenicicole waste have been identified by their combustion behavior: firstly the lif part characterized by their thermal stability due to the high lignin content and secondly the fruit bunch (ARJ) characterized by a great thermal reactivity.

Integration of solid-liquid and liquid-liquid extractions, SLE and LLE, respectively, for selective recovery of Origanum vulgare subsp. glandulosum phenolics was studied. A Two-Phase Solvent Extraction (TPSE) was performed by maceration at room temperature using a green biphasic solvent system and compared to Centrifugal Partition Extraction (CPE). Up to 69 % of phenolics were similarly recovered by both CPE and TPSE techniques using the ethyl acetate/acetic acid/water solvent system (EAW) in immiscible proportions while only 56 % of purity was reached using the conventional successive technique. Up to 19 g GAE/100 g DW of total phenolics were recovered by solid-liquid-liquid extraction (SLLE) while only 12 g GAE/100 g DW was isolated by using SLE with EAW organic phase. Comparing TPSE to organic and aqueous macerations conducted separately, a clear positive impact of combination was observed, namely more than 57 % and 83 % enhancement of the extraction yields, respectively. Such extracts exhibited a very strong antioxidant activity as shown by the antioxidant activity index (AAI) higher than 2.

International audience; An integrated screening approach was developed to assess the potential of the Botryococcus genus for the production of lipids for biofuel application (hydrocarbons and triacylglycerols). The strategy developed in this study permitted to rigorously measure mandatory parameters for the determination of strain performance – i.e. growth rate and oil content. For that purpose, mini-photobioreactors run in parallel were used together with an exhaustive lipid class analysis. The quantitative productivity measurements indicated that the ten screened strains presented very different patterns in the conditions of PBR culture, firstly run in batch, and secondly in continuous mode. Indeed, with the applied setup, only four strains presented biomass productivities close to that previously measured for the reference strain 807/1 (between 74 and 307 mg L−1 day−1 of biomass for the tested strains). HC productivity obtained under continuous light (∼14 mg L−1 day−1) was close to that measured for the strain 807/1 (∼20 mg L−1 day−1), confirming B. braunii tested strains potential for biofuel application. The analysis of the lipid chemodiversity revealed moreover that this genus should be further investigated for its polar lipids, as it suggests potential pharmaceutical applications such as production of antitumorals or immunosuppressors.

International audience; The biomass, generated after the lipid extraction from Nannochloropsis microalgae (LEM) for biodiesel production, demonstrated its suitability for both energy and nutrient recovery. The anaerobic digestion of LEM produced a minimum of 268 mL CH4 /g VS in different experiments. The codigestion of LEM and sewage sludge revealed that both wastes can be codigested without inhibition, although no synergy was observed. The methane yields barely increased 10% after pretreatments (ultrasound and ultrasound combined with alkali addition). Regarding bio-oil production from hydrothermal liquefaction process, more than 28% of the LEM was converted into bio-oil. Moreover, the aqueous phase generated during the bio-oil production was successfully utilized as nitrogen source for microalgae cultivation.

The previous chapter focused on illustrating the potential of the latest analytical equipment to discover markers or groups of markers that are characteristic of LE spoilage. Depending on the resolving power of this chemotyping equipment, these markers would be either in the form of single molecules (in the case of high or low resolution spectrometers such as NMR or MS often coupled with chromatography), or in the form of groups of these same molecules, all of which are then identified unambiguously (NMR-HR and MS-HR, often coupled with chromatography), or in the form of a chemical signature reflecting the contribution of large chemical groups present in the sample (FTIR, NIRS, Raman).

International audience; The valorization of Scenedesmus sp. microalgae byproducts was investigated, as a potential route for the production of road binders from renewable sources. Under hydrothermal liquefaction conditions, a water-insoluble viscous material was obtained in a ca. 55% yield, which consists of an oily fatty acid-based fraction mixed with organic and inorganic solid residues (up to 22%). Although the chemical composition of the obtained materials completely differs from that of petroleum-based bitumen, similar viscoelastic properties were observed in some cases, depending on the hydrothermal liquefaction experimental conditions. A rheological simple material could thus be obtained, which compared well with a bitumen reference.

Over the last decades, production of microalgae and cyanobacteria has been developed for several applications, including novel foods, cosmetic ingredients and more recently biofuel. The sustainability of these promising developments can be hindered by some constraints, such as water and nutrient footprints. This review surveys data on N2-fixing cyanobacteria for biomass production and ways to induce and improve the excretion of ammonium within cultures under aerobic conditions. The nitrogenase complex is oxygen sensitive. Nevertheless, nitrogen fixation occurs under oxic conditions due to cyanobacteria-specific characteristics. For instance, in some cyanobacteria, the vegetative cell differentiation in heterocyts provides a well-adapted anaerobic microenvironment for nitrogenase protection. Therefore, cell cultures of oxygenic cyanobacteria have been grown in laboratory and pilot photobioreactors (Dasgupta et al., 2010; Fontes et al., 1987; Moreno et al., 2003; Nayak & Das, 2013). Biomass production under diazotrophic conditions has been shown to be controlled by environmental factors such as light intensity, temperature, aeration rate, and inorganic carbon concentration, also, more specifically, by the concentration of dissolved oxygen in the culture medium. Currently, there is little information regarding the production of extracellular ammonium by heterocytous cyanobacteria. This review compares the available data on maximum ammonium concentrations and analyses the specific rate production in cultures grown as free or immobilized filamentous cyanobacteria. Extracellular production of ammonium could be coupled, as suggested by recent research on non-diazotrophic cyanobacteria, to that of other high value metabolites. There is little information available regarding the possibility for using diazotrophic cyanobacteria as cellular factories may be in regard of the constraints due to nitrogen fixation.

The use of a hydrated phosphonium ionic liquid, [P(CH2OH)4]Cl, for the extraction of microalgae lipids for biodiesel production, was evaluated using two microalgae species, Chlorella vulgaris and Nannochloropsis oculata. The ionic liquid extraction was compared to the conventional Soxhlet, and Bligh & Dyer, methods, giving the highest extraction efficiency in the case of C. vulgaris, at 8.1%. The extraction from N. oculata achieved the highest lipid yield for Bligh & Dyer (17.3%), while the ionic liquid extracted 12.8%. Nevertheless, the ionic liquid extraction showed high affinity to neutral/saponifiable lipids, resulting in the highest fatty acid methyl esters (FAMEs)-biodiesel yield (4.5%) for C. vulgaris. For N. oculata, the FAMEs yield of the ionic liquid and Bligh & Dyer extraction methods were similar (>8%), and much higher than for Soxhlet (

International audience; This paper experimentally and theoretically investigates light transfer in agar-immobilized cell cultures. Certain biotechnological applications such as production of metabolites secreted by photosynthetic microorganisms require cells to be immobilized in biopolymers to minimize contamination and to facilitate metabolite recovery. In such applications, light absorption by cells is one of the most important parameters affecting cell growth or metabolite productivity. Modeling light transfer therein can aid design and optimize immobilized-cell reactors. In this study, Parachlorella kessleri cells with areal biomass concentrations ranging from 0.36 to 16.9 g/m 2 were immobilized in 2.6 mm thick agar gels. The average absorption and scattering cross-sections as well as the scattering phase function of P. kessleri cells were measured. Then, the absorption and transport scattering coefficients of the agar gel were determined using an inverse method based on the modified two-flux approximation. The forward model was used to predict the normal-hemispherical transmittance and reflectance of the immobilized-cell films accounting for absorption and scattering by both microalgae and the agar gel. Good agreement was found between the measured and predicted normal-hemispherical transmittance and reflectance provided absorption and scattering by agar were taken into account. Moreover, good agreement was found between experimentally measured and predicted mean rate of photon absorption. Finally, optimal areal biomass concentration was determined to achieve complete absorption of the incident radiation.

Besides potential applications in the agriculture field as natural nitrogen fertilizer, N2-fixing cyanobacteria have recently gained some attentions for new applications linked to the potential production of biologically active molecules or biohydrogen. Ammonium bioproduction is also gaining attention with the potential use of microalgae in biofuels production and the concerns about the increasing needs for nitrogen substrates. This study has investigated some phenotypic traits linked to biomass production and ammonium release in multicellular cyanobacteria, Anabaena variabilis PCC 7937. It confirms that this wild-type strain has no natural ability for ammonium excretion under diazotrophic conditions. A mutant strain, A. variabilis PCC 7937-C9, was obtained after double random mutagenesis treatments with ethyl methane–sulfonate and screening in batch cultures for resistance to the effect of a glutamine synthetase inhibitor, l -methionine- d , l -sulfoximine (MSX). Although significantly characterized by shorter cell filaments, the growth parameters in photobioreactors of the mutant strain cultures were in the same range of values than those of the wild type. In the presence of MSX this strain was shown to produce extracellular ammonium, with specific rates up to 4.9 μmol NH4+ mg Chl a−1 h−1. The efficiency of this strain, estimated by its specific rate of ammonium excretion, was shown to be improved after consecutive batch cultures with increasing concentrations of MSX. Such mutant strains are of potential use for investigating ways to improve extracellular ammonium bioproduction.

International audience; The knowledge of biopolymer changes by extrusion is very important for a wide range of industrial applications that spreads from extruded food to biodegradable packaging. In this article, the formation of starch-lipid and lipid-protein complexes that occurred during the extrusion cooking of wheat flour with the addition of fatty acids was studied. Results showed that the highest barrel temperature (128.3 degrees C) promoted the formation of starch-lipid complexes in samples made up of wheat starch and wheat flour with the addition of fatty acids. The maximum formation of protein-lipid complexes (68% fatty acid bound to protein) was observed at the highest barrel temperature and water feed content (

International audience; The lipid extraction using hexane and methanol:hexane increased the biodegradability of Nannochloropsis oculata by 36% and 24% respectively. Moreover, hexane increased the methane production from raw microalgae, from 253 ± 11 to 313 ± 9 mL CH4 /g VS. Methanol:hexane did not affect the methane production, which yielded 254 ± 10 mL CH4 /g VS , mainly due to the significant changes in the biomass composition. On the other hand, the lipid extraction failed to increase the biodegradability of Chlorella vulgaris, which resulted around 44% for raw and lipid-extracted microalgae. The methane productions were 219 ± 6, 202 ± 1 and 200 ± 4 mL CH4 /g VS from raw and pre-treated microalgae using hexane and methanol:hexane respectively. Regarding the lipid extraction yields, using methanol:hexane the yields were 4.7 and 3.7 times higher for N. oculata and C. vulgaris than using hexane. The biodiesel yields were also higher using methanol:hexane, 2.4 and 1.9 times than using hexane. However, the biodiesel composition was unaffected by the solvent. The substrate to inoculum ratio influenced raw N. oculata digestion. At 1:1 VS Substrate :VS Inoculum , the methane production throughout the first days decreased but not the ultimate methane production. C. vulgaris digestion was unaffected, probably due to the biomass characteristics. Finally, the co-digestion of microalgae and sewage sludge showed no synergy, nor inhibition.

An in-depth investigation of how various illumination conditions influence microalgal growth in photobioreactors (PBR) has been presented. Effects of both the light emission spectrum (white and red) and the light incident angle (0° and 60°) on the PBR surface were investigated. The experiments were conducted in two fully controlled lab-scale PBRs, a torus PBR and a thin flat-panel PBR for high cell density culture. The results obtained in the torus PBR were used to build the kinetic growth model of Chlorella vulgaris taken as a model species. The PBR model was then applied to the thin flat-panel PBR, which was run with various illumination conditions. Its detailed representation of local rate of photon absorption under various conditions (spectral calculation of light attenuation, incident angle influence) enabled the model to take into account all the tested conditions with no further adjustment. This allowed a detailed investigation of the coupling between radiation field and photosynthetic growth. Effects of all the radiation conditions together with pigment acclimation, which was found to be relevant, were investigated in depth. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:247-261, 2016.

International audience; Here we investigate the effect of environmental pH on biomass and hydrocarbon productivity in photoautotro-phic cultures of Botryococcus braunii SAG 30.81 (race A). Successive steady-states of continuous cultures were used to study the effects of pH controlled by carbon dioxide feeds in a closed photobioreactor. At a fixed dilution rate of 0.2 d −1 , hydrocarbon productivity was found to be pH-dependent in the range 5.5 to 8.0, with an optimum at pH 6.5. pH variations from pH 6.0 to pH 8.0 had little effect on biomass productivity, nutrient requirement for biomass production, photosynthetic yield and pigment ratios, whereas acidic pH 5.5 conditions induced a slight decrease in biomass and hydrocarbon productivities as well as stressing the cells. The pH effect occurred even after a threefold increase in nitrate and phosphate concentrations in the feed culture medium, resulting in bio-mass productivity up to 8.9 g m −2 d −1 and hydrocarbon productivity up to 0.5 g m −2 d −1. Dissolved inorganic carbon data suggest that a maximum hydrocarbon content of 5.7% dry weight was reached at and above 1 mmol L −1 dissolved CO 2 and that hydrocarbon production was linearly related to CO 2 up to 2.5 mmol L −1 , whatever the N and P enrichment of AF-6 culture medium.

International audience; Although the hydrothermal liquefaction is considered a promising technology for converting microalgae into liquid biofuels, there are still some disadvantages. This paper demonstrated that the bio-oil yield can be significantly improved by adding alcohols as co-solvents and carrying out the conversion at mild conditions (< 250 degrees C), but at the expense of a reduced bio-oil quality. By adding ethanol, the bio-oil yields obtained (up to similar to 60%) were comparable to the yield obtained at severe operating conditions using only water as solvent (54 +/- 2% on average), but the quality of the bio-oil was lower. However, the main advantages of the process here described lie in the utilisation of wet microalgae (similar to 75% moisture) and alcohol concentrations which avoid both drying the microalgae and decreasing the amount of microalgae loaded in the reactor. (C) 2016 Elsevier Ltd. All rights reserved.

International audience; The aim of this work was to study the effect of the solvent N-methylmorpholine-N-oxide (NMMO) to pre-treat Nannochloropsis oculata before the anaerobic digestion process. The results indicated that the pre-treatment affects the characteristics of the cell wall, which consequently becomes more susceptible to the microorganisms attack during anaerobic digestion. The methane production was increased by 43% after the pre-treatment, from 238 ± 6 mLCH4/gVS until 339 ± 4 mLCH4/gVS. On the contrary, the methane production from Chlorella vulgaris decreased after the pre-treatment from 251 ± 4 mLCH4/gVS to 231 ± 3 mLCH4/gVS. The failure on the pre-treatment was attributed to the particular characteristics of the substrate in consequence of a previous drying step.

Mass transfer measurements were conducted on a Parallel Plate Rheometer (PPR) using the limiting diffusion current method, i.e. the polarography technique. The database constructed was exploited for the validation of the inverse method under a well-controlled unsteady shear flow. This method is based on a numerical sequential estimation. It has been applied to determine of the wall shear rate in the upper disk of the PPR. It requires the numerical inversion of the convection diffusion equation in order to apply it to instantaneous mass transfer measurements. This requires the use of electrochemical probe, which allows the determination of the local mass transfer rate for known flow kinematics. A multi-segment electrochemical probe has been used. The directional characteristics of the three-segment probe were highlighted. The directional angle effect and the frequencies of oscillations effect were studied in order to test the robustness of the inverse method within the presence of such factors. The obtained results demonstrate that the inverse method allows a good determination of the shear rate, which follows the experimental one for different cases tested in a satisfactory way.

Tetraselmis subcordiformis (formerly called Platymonas subcordiformis), a marine green alga, was previously demonstrated to photo-biologically produce hydrogen when treated with CCCP (Carbonyl Cyanide m-Chlorophenylhydrazone). The current results of our studies showed that there was a peak yield of hydrogen by T. subcordiformis at the stationary stage of its algal growth curve, suggesting that starvation of an essential element induced biochemical changes that enhanced hydrogen production by T. subcordiformis. Further investigation indicated that among nitrogen, sulphur and phosphorus (which are major components in the cultivation medium), nitrogen deprivation in the medium reduced the protein content inside the cells of T. subcordiformis, but increased the carbohydrate content over 4 times, resulting in 5.5 times increase in the hydrogen yield.

A blend of wheat flour (moisture content 11.61%) and different amounts of two commercial enzymes like GRINDAMYL (GA) amylase 1000 (0–0.1 g/kg) and GA protease 41 (0–1.0 g/kg) were extruded through a co-rotating twin-screw extruder. The effects of barrel temperature (60–120C), dough moisture (20–36%), screw speed (100–400 rpm) and different amounts of enzymes on structure of extrudates (porosity and break strength) were studied using response surface methodology. Results showed that the highest value of porosity (62.47% ± 4.07) was obtained at the highest value of barrel temperature (120C) and at the largest amounts of GA protease 41 (1.0 g/kg) or GA amylase 1000 (0.1 g/kg). However, the simultaneous addition of large amounts of both enzymes caused a negative effect on expansion degree (porosity

The influence of dynamically heat-induced aggregates on whey protein foams was investigated as a function of the thermal treatment applied to WPI using a bubbling technique. The aim was to determine the interplay between the size/shape/proportion of the heat-induced aggregates and the properties of protein foams (formation and stability). Results showed that insoluble protein aggregates were highly branched and cohesive, whereas soluble aggregates were constituted by subunits, associated by hydrophobic bonds and formed by α-La and β-Lg monomers linked by disulfide bridges. Using the bubbling procedure, protein aggregates were shown to slow down significantly foam formation. However, the rate of foam formation remained nearly unchanged for wet foams when the amount of insoluble aggregates was inferior to 5% and when their size remained lower than 100 μm. Similarly, protein aggregates did not seem to affect the destabilisation kinetics of wet foams, regardless of amount, size, shape and proportion.

International audience; The aim was to investigate the effect of dynamic thermal treatment in a tubular heat exchanger on the denaturation and foaming properties of whey proteins, such as overrun, foam stability and texture. A 2% w/v WPI Solution (pH 7.0), with and without NaCl addition (100 mM), was submitted to heat treatment at 100 degrees C. The results demonstrated that heat treatment slightly reduced overrun, whereas NaCl and heat treatment improved foam stability, enhanced texture and provided smaller bubble diameters with more homogeneous bubble size distributions in foams. The foaming properties of proteins, especially stability, were shown to depend not only on the amount of protein aggregates, but also on their size. While insoluble aggregates (larger than I pm diameter) accelerated drainage, soluble aggregates (about 200 nm diameter) played a key role on the stabilization of gas-liquid interfaces.

Torus reactors are characterized by a homogeneous fluid circulation without dead zones. Torus reactors were used for applications in biotechnology, food processing, polymerization and liquid waste treatments. The relatively simple extrapolation of performances, due to the absence of dead volume, is one of the main advantages of this reactor, with low shear stresses and an effective radial mixing allowing efficient heat dissipation. This study is based on the mixing in order to analyse the fluid circulation, mainly in turbulent flow regime, and to characterize the torus reactor with the axial dispersion plug flow model. The objective of this study is to characterize the flow and the mixing in the torus reactors in batch and continuous modes. The mixing analysis was made according to the flow parameters and to the geometrical characteristics of the reactor and impeller. The mixing in the torus reactor can be characterized by the Peclet number, Pe D , defined with torus diameter. A representative model based on plug flow with axial dispersion and partial recirculation was proposed.

When processing highly viscous fluids in scraped surface heat exchangers, it is often difficult to follow the real heat flux received by each part of the product. Only average temperatures are measured, and the process cannot always guarantee a correct thermal treatment. During a pasteurisation process, the average temperature is around 80 °C, but some parts of the product may not stay long enough at this temperature compared to the average residence time. The aim of this study is to develop a tracer in order to follow the thermal treatment of Newtonian or non Newtonian viscous fluids in an experimental scraped surface heat exchanger in conditions similar to a pasteurisation treatment. A natural coloured tracer (Betanin, from red beets) which thermal degradation is well known is used as time temperature integrator. Thermal degradation of the tracer is determined experimentally and compared with a dispersion RTD model. First results show that Betanin degradation diluted in viscous fluids follows a classical first order reaction in a batch system. However, this degradation is enhanced when mechanical treatments occur in a well identified shearing channel as well as in the SSHE, for shear rates higher than 20 000 s − 1 . The major concern was then to identify the origin of this enhancement. Temperature increase due to viscous friction was measured in the SSHE and compared with the prediction conversion factors. It was shown that thermal treatment received by the Betanin was highly dependent on the mechanical treatment delivered during the thermal treatment. Industrial relevance When processing highly viscous fluids in scraped surface heat exchangers, it is often difficult to follow the real heat flux received by each part of the product, especially in industrial apparatus. Only average temperatures are measured, and the process cannot always guarantee a correct thermal treatment. During a pasteurisation process, the average temperature is around 80 °C, but some part of the product may not stay long enough at this temperature compared to the average residence time. The aim of this study is to develop a tracer in order to follow the thermal treatment in an experimental scraped surface heat exchanger in conditions similar to a pasteurisation treatment. When this tracer is found to be appropriate, it will be used directly in industrial equipments, in order to help industrials in: first, understanding their processes; verifying that their actual operating conditions are feasible for a correct thermal treatment; if not, in optimising these operating conditions. Betanin, representative of sensitive food products treated in a scraped surface heat exchanger was found to be, not only sensitive to temperature but also to mechanical treatment. This rather unexpected result has to be taken into account very carefully by industrials in order to insure a content product quality, whereas the mechanical treatment undergone by the product can lead to an accentuated degradation of thermally sensitive products.

Adding product into the mixer exerts a strong and rapid impact during concrete mixing. Experimental data obtained from a planetary mixer in a full-scale concrete plant under laboratory conditions show that the state of mixture progress with mixing time is well described by the mixing power evolution. More specifically, a reliable method for detecting the time corresponding to the transformation of a mixture from a cohesive granular material into a granular paste (i.e. the so-called “transition time”), through use of a mixing power measurement, will be presented herein. Moreover, once this transition has been achieved, mixing power consumption will be related to mixture rheology and then to mixer geometry by means of a simplified hypothesis. This equation can also be obtained via a dimensionless analysis. Lastly, it will be shown that mixture behavior beyond the transition point is well fitted by a hyperbolic equation. The corresponding mixing power evolution can then be predicted by the level of power at this transition time. These results are suitable for application to online process monitoring.

International audience; The aim was to investigate the effect of dynamic thermal treatment in a heat exchanger on the denaturation and aggregation of whey proteins. A 2% w/v WPI solution (pH 7.0), with or without NaCl addition (100 mM), was submitted to heat treatment at 100 degrees C. At low ionic strength, a nearly complete denaturation was observed, while the heat-treated samples at 100 mM ionic strength registered only 10% denaturation. It was shown that not only denaturation was reduced by the presence of NaCl, but also that the size of the aggregates formed during heat treatment was far smaller and remained essentially below 1 mu m. Surface tension measurements showed a faster adsorption and lower sigma values for the non-polymerized proteins, whereas insoluble aggregates played only a poor role on the sigma curves. Finally, experimental results demonstrated the strong interaction between ionic strength and dynamic thermal treatment on protein aggregation and properties.

The mixing at a molecular scale (micromixing) plays an important role on selectivity, yield and quality of final products of a large range of competing fast chemical reactions. In this study, we have compared, by the use of iodide–iodate reaction tests, the micromixing in two reactors, the first one is the standard batch stirred reactor and the second is the torus reactor. Various conditions of agitation and feed locations were used for this study. A comparative analysis of the micromixedness ratio (α) in the two reactors was carried out on the basis of the local rate of specific energy dissipation.

Alginates are natural polysaccharides that are extracted from brown seaweeds and widely used for their rheological properties. The main step in the extraction protocol used in the alginate industry is that of alkaline extraction. A batch process is used for this step, which is time-, water-, and reactant-consuming. The possibility of extracting by reactive extrusion was investigated. The reactive extrusion process appeared to be more efficient than the batch process for the alkaline extraction of alginates from Laminaria digitata in several key ways: Time demand is reduced from about an hour to only few minutes, water and reactant requirements are divided by more than a factor 2, extraction yield is 15% higher (relative enhancement), and the rheological properties of the product were all enhanced. Hence, reactive extrusion could be an interesting alternative process for the alginate industry to produce high rheological properties alginates.

Effects of adding Fe 2+ ions in photoheterotrophic cultivation of Dunaliella salina on growth and β-carotene synthesis were investigated. Different concentrations of Fe 2+ ions and organic carbon source (acetate and malonate) were studied. A significant increase of cellular β-carotene content was observed, with a maximum value of 70 pg/cell in a culture enriched with 67.5 mM of acetate and 450 μM of FeSO 4 and 33 pg/cell in the case of 67.5 mM of malonate and 450 μM of FeSO 4 . For comparison, the well-known nitrate starvation protocol was applied, and 35 pg/cell of β-carotene were obtained. By inducing an oxidative stress, Fe 2+ ions revealed to stimulate β-carotene synthesis, especially when acting in the presence of the carbon source. Furthermore for some concentration of Fe 2+ ions and organic carbon source, the loss in cells division was reduced compared to nitrate starvation.

The convective diffusion problem near small electrodes is solved numerically using finite volume method (direct problem). The results obtained are first used to define the limits of the quasi-steady state Leveque solution for a rectangular and circular probe. After, the algorithm is integrated to an inverse sequential method in order to obtain the wall shear rate from the measurements of the limiting diffusion currents. The results are compared with the classical techniques of calculation of wall shear rate as the quasi-steady solution, transfer function methods and the Leveque solution with transient correction.

International audience; Water quality and water management are worldwide issues. The analysis of pollutants and in particular, heavy metals, is generally conducted by sensitive but expensive physicochemical methods. Other alternative methods of analysis, such as microbial biosensors, have been developed for their potential simplicity and expected moderate cost. Using a biosensor for a long time generates many changes in the growth of the immobilized bacteria and consequently alters the robustness of the detection. This work simulated the operation of a biosensor for the long-term detection of cadmium and improved our understanding of the bioluminescence reaction dynamics of bioreporter bacteria inside an agarose matrix. The choice of the numerical tools is justified by the difficulty to measure experimentally in every condition the biosensor functioning during a long time (several days). The numerical simulation of a biomass profile is made by coupling the diffusion equation and the consumption/reaction of the nutrients by the bacteria. The numerical results show very good agreement with the experimental profiles. The growth model verified that the bacterial growth is conditioned by both the diffusion and the consumption of the nutrients. Thus, there is a high bacterial density in the first millimeter of the immobilization matrix. The growth model has been very useful for the development of the bioluminescence model inside the gel and shows that a concentration of oxygen greater than or equal to 22 % of saturation is required to maintain a significant level of bioluminescence. A continuous feeding of nutrients during the process of detection of cadmium leads to a biofilm which reduces the diffusion of nutrients and restricts the presence of oxygen from the first layer of the agarose (1 mm) and affects the intensity of the bioluminescent reaction. The main advantage of this work is to link experimental works with numerical models of growth and bioluminescence in order to provide a general purpose model to understand, anticipate, or predict the dysfunction of a biosensor using immobilized bioluminescent bioreporter in a matrix.

International audience; The microalga Botryococcus braunii has been studied for its hydrocarbon biofuel production potential. The range of the lipids it synthesizes cannot be readily profiled, because their main chemical class standards (long chain al-kenes and botryococcenes) are at present unavailable. The aim of this study was to develop a direct, specific GCMS analysis method for the rapid chemotyping of these lipids. The SIM (Selected Ion Monitoring)-GCMS program we developed discriminates classes and subclasses of the targeted molecules through their main chemical motifs identified with fragment ions of specific m/z selected by unsupervised chemometrics. Our validation results indicate that the SIM mode enhanced their detection by significantly increasing the signal-to-noise ratio ca. 20-fold. The profiling results from TL extracts of diverse B. braunii strains show that under the culture conditions tested, these strains could be distinguished by their chemical signatures, which also signaled different culture conditions involving various physiological states. We were able to make a rapid estimate of the biofuel potential of these strains, focusing on alkenes and botryococcenes. The direct injection SIM-GCMS method was successfully applied here for rapid chemotaxonomy, displaying good sensitivity and specificity for new high molecular weight hydrocarbons from B. braunii.

Centrifugal Partition Chromatography (CPC) is a separation process based on the partitioning of solutes between two partially miscible liquid phases. There is no solid support for the stationary phase. The centrifugal acceleration is responsible for both stationary phase retention and mobile phase dispersion. CPC is thus a process based on liquid–liquid mass transfer. The separation efficiency is mainly influenced by the hydrodynamics of the phases in each cell of the column. Thanks to a visualization system, called “Visual CPC”, it was observed that the mobile phase can flow through the stationary phase as a sheet, or a spray. Hydrodynamics, which directly governs the instrument efficiency, is directly affected during scale changes, and non-linear phenomena prevent the successful achievement of mastered geometrical scale changes. In this work, a methodology for CPC column sizing is proposed, based on the characterization of the efficiency of advanced cell shapes, taking into account the hydrodynamics. Knowledge about relationship between stationary phase volume, cell efficiency and separation resolution in CPC allowed calculating the optimum cell number for laboratory and industrial scale CPC application. The methodology is highlighted with results on five different geometries from 25 to 5000 mL, for two applications: the separation of alkylbenzene by partitioning with heptane/methanol/water biphasic system; and the separation of peptides by partitioning with n-butanol/acetic acid/water (4/1/5) biphasic system. With this approach, it is possible to predict the optimal CPC column length leading to highest productivity.

Summary The formation of starch–lipid complexes plays an important role in extruded products. The effect of gluten proteins on thermal conditions at which the starch–lipid complexes formed during extrusion cooking of wheat flour with the addition of oleic acid was evaluated, considering wheat starch as a reference. The presence of gluten proteins in wheat flour extrudates brought about a reduction of the formation of starch–lipid complexes compared to blend of wheat starch and oleic acid extruded at the same operating conditions (melting enthalpy: 0.4 vs. 1.6 kJ kg−1). Moreover, the lubricant effect of oleic acid observed during extrusion of wheat starch (low values of specific mechanical energy and residence time) was not found during extrusion of wheat flour with addition of oleic acid because of the interaction between gluten proteins and oleic acid. This research points out the importance of proteins on biopolymer modifications and their effect on extrudate quality.

An ultra high-pressure homogenizer was used to treat whey protein isolate solutions (3%, w/w). The treated solutions (up to 300 MPa) were characterised for both physico-chemical properties (particle size distribution, surface hydrophobicity and structural conformation) and functional properties (solubility, foaming stability and interfacial rheology). Dynamic high-pressure treatment did not affect the conformation of the proteins (determined by micro-calorimetry, size-exclusion chromatography and electrophoretic technique). This treatment dissociated large protein aggregates leading to unmasking of the buried hydrophobic groups without affecting protein solubility. Interactions may then occur between these groups that enhance the viscoelasticity of air-water interfaces (assessed by drop tensiometry) and improve foam stability (evaluated by sparging method). Dynamic high-pressure-treated whey proteins showed better foaming and stabilising properties.

An experimental investigation of a scaled-down model of an industrial exchanger, using an electrochemical technique, was undertaken in order to show the presence of hydrodynamic heterogeneities at low axial Reynolds number. Heterogeneities were revealed in the bowls with respect to the generalised Taylor number as the result of the perturbations added to the flow by blade rotation at both ends of the exchanger. Shear heterogeneities associated to flow visualisations were correlated to temperature heterogeneities observed in the bowls. Shear fluctuations were revealed in the scraped part describing two distinctive zones at low rotation speed caused by varying viscosity in the flow field. A complex spiral flow was observed by flow visualisation characterising a mass transfer evolution comprised between these two distinctive zones at low Taylor number.

A torus reactor was used to perform hydrolysis of casein with a protease immobilized on beads. Chitosan beads with two different sizes were tested as immobilization matrices. The mechanical resistance of beads in the torus reactor was tested for different times and rotation speeds. Chitosan beads were considered to be suitable as an immobilizing support. The more stable hydrolysis rates in successive assays were obtained with the protease grafted onto the largest chitosan beads. The kinetics parameters of free and immobilized enzymes were determined and compared in batch stirred tanks and torus reactors. Immobilization decreased the enzyme activity to only 5% of the free enzyme activity. No significant differences for apparent kinetic constant ( Km) were observed between immobilized and free enzyme. The apparent reaction rate constant (Vmax) was 25 times less with immobilized enzyme in the torus reactor than with free enzyme in the batch reactor. © 2004 Elsevier Ltd. All rights reserved.

Viscous products treated in a scraped surface heat exchanger receive a thermal treatment as well as a mechanical treatment. The new method developed by Mabit et al. [J. Food Engrg. 57 (2) (2003) 165] using starch as a marker for the shearing treatment was performed in order to show the influence of blades movement and flow pattern on shearing conditions. Two different flow regimes with respect to the generalised Taylor Number Ta g were investigated: a laminar regime with Taylor vortices and a weakly turbulent one. The blade rotation without scraping in the annulus space can be sufficient to apply a shear treatment above 20,000 s −1 . The product is submitted to the highest shear treatment for high rotational speed with a laminar regime with Taylor vortices. Blades scraping creates high wall shear rates, Taylor vortices improve radial mixing and renew product to be treated at the wall surface. The quantity of stressed product is directly influenced by the flow behaviour and the product residence time in the exchanger.

The electrodiffusion technique was performed in order to investigate the shear rate on a scraped surface heat exchanger. Microelectrodes were placed inside: the walls of the outer cylinder; the inlet and outlet bowls; the rotor and the blades. Highly viscous Newtonian fluid (Emkarox HV45 solutions) and non-Newtonian model fluid (aqueous solutions of CMC) were used. The electrodiffusion method allowed us to measure wall shear rates. Maximum shear rate was observed at the scraping surface and caused by blades scraping, high shear rate was also measured on the leading edge of the blades. In the other parts of the exchanger, shear rate remained low but the development of Taylor vortices completely modified the scraped surface heat exchangers behaviour inside the surface of the bowls. A dimensionless representation of the friction factor was established for the inner and outer wall surface of the exchanger.

A new high pressure homogeniser going up to 350 MPa was used to produce fine emulsions stabilised by methylcellulose for food applications. The objective of this study was to evaluate the effect of homogenising pressure on emulsifying and stabilising properties of methylcellulose, a food macromolecule extensively used as stabiliser in emulsions. Oil droplet size distributions of the emulsions were measured by laser-light scattering; rheological properties were characterised with a coaxial cylinder rheometer; and stability was evaluated by heating of the emulsions. Influence of homogenising pressure on interfacial properties (adsorption kinetics, interfacial tension and rheological behaviour) of the polymer was also studied at different pressure treatments. The results showed significant modifications in the structure and the texture of emulsions with increasing homogenising pressure. Homogenised methylcellulose solutions showed weaker thickening and stabilising properties compared to the one of the native methylcellulose.

This works deals with the mechanical treatment realised in a surface scraped heat exchanger (SSHE) and consequence on products. In this type of apparatus, the presence of high shear rates is demonstrated and added to the thermal treatment. An innovative method was developed to measure the quantity of product that is subjected to high shear in the SSHE. This method used a starch suspension, which was sensitive to mechanical treatment. The starch granule diameter increased with the shear rate applied to the suspension. The increase of granule diameter measured by laser granulometry yielded the volume fraction of stressed starch. This method indicated that granules started to swell at a rotational speed of 6.5 rps and that 37% of starch is stressed at 10 rps. These results are explained by the role of the blades and confirm the presence of high wall shear rates. It was shown that starch granules were stressed and that Taylor vortices did not generate sufficient high shear rates in a SSHE to modify the starch granules. The mechanical stress was correlated to the shear rates applied. The starch granules became sensitive to shear treatment at 20,000 s−1 and this value was exceeded in the SSHE by the rotation of blades.

The objective of the work is to create a two-effect product composed by microcapsules containing insecticide suspended in concentrated disinfectant solution. A two-step microencapsulation process has been performed with a first step corresponding to the formation of an oil/water (o/w) dispersion in a static mixer and a second step to the microencapsulation by interfacial polymerisation in a stirred tank reactor. Microcapsules are characterized by a mean diameter of 30 μm in order to ensure their suspension in the disinfectant solution. Microcapsules wall is made of polyurea and release rates monitored by pH-measuring in the disinfectant solution, are found to be very low, allowing a good compatibility of insecticide and disinfectant.

The present work deals with the use of a torus mixer for the formation of liquid-liquid dispersion. The objective is to determine the performance of the torus reactor to form the primary emulsion of the microencapsulation process of an active product by a solvent evaporation technique. The encapsulated product is dissolved in an aqueous phase, which is emulsified into a solution of the polymer in methylene chloride to form a water/oil emulsion. The methylene chloride is gradually removed from the droplets by evaporation. Hard microcapsules are obtained when the solvent is completely removed. The formation of the water/oil primary emulsions is the key step to control the size distribution of the microcapsules.The characteristics of the dispersed phase of the water-in-oil emulsion produced in a torus mixer in batch and continuous conditions is determined by an optical method based on the use of the microscope connected to a CCD camera. The flow inside the torus mixer is directly linked to the rotation speed of the impeller. The effect of the rotation speed of the impeller and the dispersed phase volume fraction of the liquid-liquid dispersion is analyzed. The experimental data are expressed by a correlation giving the mean droplet diameter in function of the Weber number and dispersed phase concentration. The influence of the superimposed throughput, for the continuous process, on the size distribution of the dispersed phase is also taken into account.

An ultra high-pressure homogenizer (20 to 350 MPa) was used to realize fine food emulsions stabilized by soy proteins. The first aim of the work was to understand how dynamic high-pressure processing affects soybean globulin conformation. Then, the effect of homogenizing pressure on the emulsions structure and rheology was investigated. High-pressure homogenization caused denaturation of proteins due to strong mechanical forces and high temperatures encountered in the valve. Droplet sizes of emulsions were greatly reduced with high-pressure homogenization and Newtonian liquid emulsions were converted into shear-thinning emulsion gels by homogenization at pressures above 250 MPa. Hydrophobic interactions between proteins were supposed to cause the gel-like network structure of emulsions.

Centrifugal partition chromatography (CPC) is a support-free liquid-liquid separation process that depends for efficiency on the behavior of the two liquid phases. Hydrodynamics of phases was studied according to flow rate and centrifugal acceleration, using a transparent column and a stroboscopic video system. For the heptane-methanol two-phase system, three main flow regimes - stuck film, oscillating sheet, and atomization - are observed, highlighting the coriolis acceleration effect as well as the influence of the column shape. Mass transport in the CPC column is modeled by a plug flow with axial dispersion and mass transfer with a stagnant volume. Model parameters (residence time, Peclet number, partition ratio, and mass-transfer coefficient) are fitted on solute residence-time distribution. Off-column dispersion is an important source of peak broadening in CPC, whereas its irregular geometry provides a plug flow for mobile phase. Importance of flow pattern on mass transfer is demonstrated. CPC interest for preparative applications is confirmed.

Initially developed for the dairy industry, the very high pressure homogenisation (>100 MPa) is now also applied in the pharmaceutical sector and in biotechnology (breaking cells for biomass extraction). The use of this technology to make fine food emulsions and to modify functional properties of macromolecules seems to be promising. Thus the objective of this study was to understand the effect of homogenisation forces on the mechanical degradation of a model polymer extensively used in food, cosmetic and pharmaceutical preparations: the methylcellulose. Degradation of the polymer was studied in a pressure range in the homogenising valve from 20 to 350 MPa. It was observed that as the pressure imposed by the homogeniser increased, the intrinsic viscosity decreased. Intrinsic viscosity decrease was correlated to apparent changes in the average molecular weight of the polymers obtained by size exclusion chromatography coupled on-line with multi-angle laser light scattering and refractive index detection (SEC/MALLS/RI). The strong elongational flow encountered by the polymer at the entrance of the valve of the high pressure homogeniser device may bring sufficient energy to disrupt covalent bonds. Consequently, as shown by flow behaviour the thickening properties of this polymer were also reduced.