Modelling the dehydration kinetics of four onion varieties in an oven and a solar greenhouse.

The Oven drying kinetics mathematical modelling of four Senegalese onion varieties is carried out in the temperature range from 50 °C to 70 °C. The R2 (dispersion test) and the χ2 (fit test) between the experimental data and the values predicted by the models show that whatever the temperature and the variety, the Verma et al. model is the one that best fits the oven drying kinetics. The R2 average and χ2 average values for the Galmi Violet, Safari, Gandiol F1 and Orient F1 are respectively between 0.9848 to 0.9961 and 0.0010 to 0.006. This best model is validated on the solar greenhouse drying kinetics at variable temperatures during the drying process. The Drying Characteristic Curves (DCCs) have identical patterns for the four onion varieties and are described with third order polynomials in the reduced moisture content range from 0.1 to 0.7. The Galmi Violet, with the slowest drying rate, is the limiting variety, followed by the Safari, Gandiol F1 and Orient F1. Furthermore, the critical and equilibrium reduced moisture content deduced from the DCCs are respectively between 0.55 to 0.70 and 0.05 to 0.15.

Laminar flow-based electrochemical microreactor for efficient regeneration of nicotinamide cofactors for biocatalysis.

One of the long-standing challenges in biocatalysis is the search for methods to continuously regenerate essential cofactors such as NADH that would enable a wide range of enzymes to be used in the more environmentally friendly synthesis of chiral fine chemicals including pharmaceuticals, cosmetics, and food additives. This communication reports a microreactor-based cofactor regeneration method that exploits the microfluidic phenomenon of laminar flow: a reactant stream and a buffer stream are introduced in a microchannel and continue to flow side by side without turbulent mixing between two electrodes that cover opposing channel walls. Adjustment of the flow rate ratio of the two streams in laminar flow enables focusing of the reactant stream close to the cathode, thereby reversing a normally unfavorable reaction equilibrium essential for cofactor regeneration. The absence of a bulk phase in these microreactors prevents the undesired reverse reaction to take place, which has prevented the use of electrochemical cofactor regeneration in macroscale processes. Here, we demonstrate the regeneration of NADH with conversion efficiencies as high as 31%. We also show the subsequent in situ conversion of an achiral substrate, pyruvate, into a chiral product, l-lactate, within this microreactor.