The light attenuation in a photobioreactor is determined using a fully predictive model. The optical properties were first calculated, using a data bank of the literature, from only the knowledge of pigments content, shape, and size distributions of cultivated cells which are a function of the physiology of the current species. The radiative properties of the biological turbid medium were then deduced using the exact Lorenz-Mie theory. This method is experimentally validated using a large-size integrating sphere photometer. The radiative properties are then used in a rectangular, one-dimensional two-flux model to predict radiant light attenuation in a photobioreactor, considering a quasi-collimated field of irradiance. Combination of this radiative model with the predictive determination of optical properties is finally validated by in situ measurement of attenuation profiles in a torus photobioreactor cultivating the microalgae Chlamydomonas reinhardtii, after a complete and proper characterization of the incident light flux provided by the experimental set-up.

It is well-known that the response of photosynthetic microorganisms in photobioreactor (PBR) is greatly influenced by the geometry of the process, and its cultivation parameters. The design of an adapted PBR requires understanding of the coupling between the biological response and the environmental conditions applied. Cells culture under well-defined conditions are thus of primary interest. A particular labscale PBR has been developed for this purpose. It is based on a torus shape, that enables light to be highly controlled while providing a very efficient mixing, especially along the light gradient in the culture, that it is known to be a key-parameter in PBR running. A complete characterization of hydrodynamic conditions is presented, using computational fluids dynamics (CFD). After validation by comparison with experimental measurements, a parametric study is conducted to characterize important hydrodynamics features with respect to PBR application (light access, circulation velocity, global shear-stress), and then to investigate a possible optimization of the process via modification of the impeller used for culture mixing. The final part of the study is devoted to a detailed investigation of mixing performance of the torus PBR, by numerically predicting dispersion of a passive tracer in various configurations. The high degree of mixing observed shows the great potential of such innovative geometry in the field of photosynthetic microorganisms cultivation, especially for the design of a lab-scale process to conduct experiments under well-controlled conditions (light and flow) for modeling purpose.

Currently, there is major consumer concern about dietary salt intake worldwide. However, even with the development of contemporary preservation practices, sodium chloride is still essential in processed meat products. Despite a long history of use, salt is now seriously controversial in food due to health concerns that are mostly related to high blood pressure and cardiovascular risks. Changes in meat processing methods have reduced those potential risks, but different perceptions continue to shape how consumers and society view dietary salt. The current consumer demand for additive‐free food, such as the clean‐label movement, has renewed consumer willingness for naturalness in food products.

No abstract

The effects of heat-stress kinetics on the viability of Escherichia coli were investigated. Cells were exposed to heat-stress treatments extending from 30 to 50 degrees C, with either a slope (40 min) or a shock (10 s), both followed by a 1-h plateau at 50 degrees C in nutritive medium. A higher survival rate was observed after the slope than after the shock, when both were followed by a plateau, so the heat slope induced a certain degree of thermotolerance. This tolerance was partly (i) linked to de novo protein synthesis during the subsequent plateau phase, and (ii) abolished after rapid cooling from 50 to 30 degrees C, which means that cellular components with rapidly reversible thermal properties are involved in this type of thermotolerance. The heat-slope-induced thermotolerance was chiefly linked to the maintenance of the plasma membrane integrity (preservation of structure, fluidity, and permeability), and not to GroEL or DnaK overexpression. Moreover, the high level of cell mortality induced by the heat shock could be related to changes in the membrane integrity.

No abstract

No abstract

No abstract