Régis Baron

Kinetics modeling of alginate alkaline extraction from Laminaria digitata

Alginates being depolymerized during their alkaline extraction, reducing extraction time could help producing higher rheological quality alginates. The purpose of the present work is to study fresh Laminaria digitata destructuration during alkaline extraction and its link to extraction kinetics. Both alginate extraction yield and mean diameter of algae particles were followed for different values of agitation level and initial size of algae pieces. Results highlighted the existence of a link between extraction yield and algal destructuration. Those elements and the specificity of L.digitata structure have been taken into account to propose a kinetics model based on a fluid-particle reaction with decreasing size particles. The model parameters have been adjusted thanks to acquisition data and its predictive capacity was assessed by validation data. Provided predictions appeared to be relevant and the model structure suitability was confirmed, as extraction yield kinetics specific shape was quite reliably described.

Transient initial phase in continuous culture of Isochrysis galbana affinis Tahiti

Starting microalgae continuous culture generally includes a preliminary batch culture to obtain sufficient cell density. It is possible to apply continuous regime from the beginning of the culture (IC mode) rather than to begin by an initial batch (IB mode). It is our purpose to check that both initial modes lead to identical steady-state cell characteristics. The microalga Isochrysis galbana affinis Tahiti was used for this comparative study. With an initial cell density o f5◊1 0 5 cell ml ‐1 and a dilution rate of about 1.0 d ‐1 , both IB and IC modes led to identical cell density once steady-state is reached between 6 and 8 d after inoculation in the two cases. Cell concentration of chlorophyll a and pheopigment a were found to be similar for IB and IC modes at steady-state. Initial culture conditions did not influence saturation irradiance and oxygen consumption rate, which were found to be 650 ± 143 µmol phot m ‐2 s ‐1 and 1.54 ◊ 10 ‐3 ±1 0 ‐5 µmol O2 ml ‐1 min ‐1 , respectively. At steady-state, nutrient cell uptakes were qN = 83.3 ± 2.0 fmol N cell ‐1 d ‐1 for NO3 ‐ and qP = 5.5 ± 0.4 fmol P cell ‐1 d ‐1 for H2PO4 ‐ and did not exhibit significant differences between IB and IC modes. Under the prevailing experimental conditions, results show that IC mode involved very similar steady-state cell characteristics when compared to IB mode subsequent steady-state. IC mode could be an attractive alternative especially for experimental laboratory studies, as it should lead to higher flexibility in starting continuous cultures.

Decrease in dynamic viscosity and average molecular weight of alginate from Laminaria digitata during alkaline extraction

Alginates are natural polysaccharides that are extracted from brown seaweeds and widely used for their rheological properties. The central step in the extraction protocol used in the alginate industry is the alkaline extraction, which requires several hours. In this study, a significant decrease in alginate dynamic viscosity was observed after 2 h of alkaline treatment. Intrinsic viscosity and average molecular weight of alginates from alkaline extractions 1–4 h in duration were determined, indicating depolymerization of alginates: average molecular weight decreased significantly during the extraction, falling by a factor of 5 between 1 and 4 h of extraction. These results suggested that reducing extraction time could enable preserving the rheological properties of the extracted alginates.

Influence of Crassostrea gigas (Thunberg) sexual maturation stage and ploidy on uptake of paralytic phycotoxins.

The purpose of this study was to assess paralytic phycotoxin uptake in diploid and triploid oysters at two stages of their sexual cycle corresponding to their status in early summer (June) and winter (November). Samples of diploid and triploid oysters were exposed to a toxic culture of Alexandrium minutum for 4 days in each season. No significant differences in filtration or clearance rates were observed during either November or June experiments. When diploid oysters were at resting stage (November), toxin uptake showed no significant difference between the ploidy classes. In contrast, when the diploid oysters were at the peak of their sexual maturation (June), the triploid oysters were seen to accumulate almost double the amount of paralytic toxins as the diploid ones.

Numerical and Experimental Study of a Continuous Electrostatic Smoking Process

The smoking process is a batch one with long duration processing (some hours). Deposition of smoke particles can be enhanced by electrostatic precipitation. However, a better knowledge of the fundamental physics is needed to optimize the process. We carried out experimental and numerical studies to obtain essential information on the smoke flow. First, experiments physically characterized the wood smoke. These measures lead us to study the turbulent two-phase flow using an algebraic slip model. The main coupling with electrical forces is taken into account through the slip velocity. Various assumptions were tested concerning the coupled phenomena in order to build an algorithm that is able to simulate these phenomena. Numerical resolutions are compared with data from the literature on a simple electrostatic precipitator (three wires between two plates). Simultaneously, experiments were performed on a simplified scaled-down model of the smoking process (wires and one plate). The results of particle image velocimetry show clearly that the electrostatic precipitation phenomenon is effective above a threshold voltage and is significantly influenced by geometry of electrodes. Experiments and numerical resolutions underwent a validation phase. A small-size industrial demonstrator, of which the promising results will not be discussed in this paper, was conceived by exploiting the presented works.

Odor Modification in Salmon Hydrolysates Using the Maillard Reaction

The aim of this work was to study the effect of adding sugar during proteolysis to promote the Maillard reaction and mask the initial fish odor and off-flavors generated. An experimental design, based on the Doehlert plan, was used to study the influence of hydrolysis conditions (time, temperature, sugar, and antioxidant addition) on the odor characteristics of hydrolysates, soluble protein levels, and amino acid content. Results showed that the lowest level of sugar (10 g of D-xylose added to 1 kg of by-products) was enough to develop a grilled odor in hydrolysates. In the hydrolysis conditions used—i.e., enzyme inactivation at 95°C for 30 min—hydrolysis temperature had no effect on grilled odor production but significantly affected the soluble protein fraction, as did hydrolysis time. Soluble protein content and essential amino acid content increased with the enzymatic reaction but were not modified by adding sugar. Hydrolysis conditions that promote Maillard reactions while keeping a nutritional balance have been identified.

Elements for optimizing a one-step enzymatic bio-refinery process of shrimp cuticles: Focus on enzymatic proteolysis screening

Graphical abstract

Valorization of the Macroalgae Sargassum Muticum by Enzymatic Hydrolysis, Interest of Surfactants to Improve the Extraction of Phlorotannins and Polysaccharides

The use of surfactants to improve enzymatic hydrolysis of the macroalgae Sargassum muticum has been investigated. Visible absorption spectroscopy has been used to quantify the solubilization of both polysaccharides and phlorotannins in the hydrolysates.   After total extraction, results showed that Sargassum muticum contained 2.74% (expressed in percent of the dry weight of the algae) of phlorotannins whose 32 % were in the cell wall. This result shows that it is important to access to the parietal phlorotannins. To reach this objective, we chose the enzymatic approach for destructurating the cell wall of the algae. The use of 5% dry weight (DW - 5% by weight of hydrolyzed algae) of an enzymatic mix containing a commercial beta-glucanase, a commercial protease and an alginate lyase extracted from Pseudomonas alginovora led after 3 hours of hydrolysis to the solubilization of 2.43% DW polysaccharides and 0.52% DW phlorotannins. The use of 0.5% volume of the surfactant Triton® X-100 with 10% DW of the enzymatic mix has allowed to reaching the value of 2.63% DW of solubilized phlorotannins, that is 96% of the total phenolic content.   The use of non-ionic surfactant, combined to enzymatic hydrolysis, showed an increased efficiency in disrupting cell wall and solubilizing phlorotannins in Sargassum muticum.

Modelling the Environmental Variable Influences on the Detoxification Kinetics on Mussels Mytilus Edulis Containing Lipophilic Toxins

Abstract The purpose of this study is to implement models to describe detoxification kinetics of Blue mussels Mytilus edulis containing lipophilic phycotoxins taking into account environmental variables (cholorophyll and temperature). The Norwegian monitoring data are among the most interesting to be exploited to work on the establishment of kinetics predictive models. The work described here is based on the parametric adaptation of simple dynamic models from these data. The detoxification rate was chosen to be linearly dependant of chlorophyll and temperature. The different assays permit to put in evidence the influence of these two variables on the kinetics.