Catherine Porte

Effect of Mixing Conditions on the Behavior of Lipoxygenase, Peroxidase, and Catalase in Wheat Flour Doughs

ABSTRACT The effect of mixing has been tested on the extractable activities of lipoxygenase, peroxidase, and catalase from dough after 2, 5, and 20 min of mixing, and 30 min of rest period after 20 min of mixing. Different mixing conditions have been studied including temperature, atmosphere, speed, amount of water added to the dough, buffer solutions between pH 3.6 and 7.5 added to the dough, and different additives (linoleic acid, guaiacol, hydrogen peroxide, ascorbic acid, cysteine, yeast, and sodium chloride). In all the mixing conditions tested, the dough peroxidase activity remains equivalent to the initial flour activity, whereas losses in lipoxygenase and catalase activities largely varied according to mixing conditions. The results show that a self-destruction mechanism as well as physicochemical denaturation are responsible for these losses. Lipoxygenase losses seem mainly associated with the former mechanism, whereas catalase losses are highly increased in acidic conditions (physicochemical den...

Study of the solubility and the metastable zone of 1,3-dihydroxyacetone for the drowning-out process

Abstract The 1,3-dihydroxyacetone (DHA) is an important raw material in the cosmetic industry for its skin pigmentation property. The DHA is highly soluble in water, which leads to a very important viscosity value and a huge metastable zone width. In addition, the DHA is a heat-sensitive substance. The drowning-out process (water-out or salting-out) is then necessary to reduce the solubility and to favor the mobility of the molecular species in solution. In this work, the solubility curves of DHA in different water/ethanol mixtures have been established experimentally. The turbidimetric method is used successfully to study the metastable zone in the water/ethanol mixture. The results show that the metastable zone is large, both the dissolution and the crystallization of DHA are time consuming, which could be due to the low diffusivity in the high-concentration solutions and at low temperatures.

Kinetic modelling of the degradation of the α-tocopherol in biodiesel-rape methyl ester.

The aim of this work was to study the influence of three major factors (light, atmospheric oxygen, temperature) responsible for the degradation of tocopherols. The evolution of alpha-tocopherol contents was analysed by high-performance liquid chromatography. Taguchis experimental design was applied to establish a mathematical model of alpha-tocopherols degradation in function of the studied parameters especially in a domain of temperature between 50 degrees C and 150 degrees C. The results show that the major factor is the temperature, especially above 100 degrees C. Light is a negligible factor, meaning that degradation is mainly due to an autoxidation phenomenon. Moreover, only interactions between temperature and atmospheric oxygen have been observed especially above 100 degrees C. The mathematical model was validated for a temperature of 75 degrees C and permits to calculate a predictive speed of degradation in this domain.

COMPARISON OF KINETIC MODELS FOR THE AQUEOUS SOLID-LIQUID EXTRACTION OF TILIA SAPWOOD IN A CONTINUOUS STIRRED TANK REACTOR

The kinetic study of the aqueous extraction of Tilia sapwood was based on temperature, while all the other factors were kept constant. Several models were used and compared to explain the kinetics of the aqueous solid-liquid extraction of Tilia sapwood. For each model, the rate constant, the equilibrium extraction capacity, and the initial extraction rate were evaluated to analyze the suitability of these kinetic models to describe the leaching process for temperatures ranging from 313 to 363 K. The pseudo first-order model could not be applied during the whole of the process. The Elovich model provided a good degree of correlation (from 0.929 to 0.988) and could be applied all along the extraction process. The pseudo second-order model was satisfactorily applied, with coefficients of correlation over 0.998, showing that it perfectly described the process. A physical explanation of these models was finally proposed.

Modeling of Fenton Reaction for the Oxidation of Phenol in Water

Phenol is an organic pollutant found in various types of industrial wastewater. Due to its bactericidal properties, it is difficult to eliminate it by classic treatment methods. In this work, the degradation of this compound by Fenton reaction at mild temperature and pressure conditions is studied. An experimental design was applied in order to quantify the influence of operating parameters on the efficiency of this method. The field of study was defined between 20 and 50^C for the temperature, 1 and 4 g L-1 for the phenol concentration, 10 and 28 for the H2O2 to phenol molar ratio, and 0.02 to 0.08 for the Fe(II) to phenol concentration ratio. It was shown that the temperature and the amount of catalyst have a strong influence. A model giving the decrease of COD was established. The COD decrease was between 40% and 72% and phenol had totally disappeared.

Setup of glycine continuous synthesis by ammonolysis of monochloroacetic acid

This article describes the continuous production of glycine by catalytic ammonolysis of monochloroacetic acid in an aqueous medium. The synthesis and crystallization of glycine are carried out in a battery of three stirred double-jacketed reactors while temperature and pH values are controlled. The results of the kinetic study allow one to calculate the residence time in each tank for a desired conversion ratio and are first checked with the setup. Then, some parameters (concentration of reagents, regulation of pH, residence time, catalyst) are modified to improve the final yield in crystallized glycine. The best yield resulting from a flow process (96.6%) is better than that resulting from a batch process (93%) and is obtained in the following conditions: the first step is performed at 75°C and pH 5.4 with a 10 mol L−1 monochloroacetic acid solution and a 17 mol L−1 ammonia aqueous one with a 0.2 molar ratio of hexamethylenetetramine; the second step is carried out at 75°C and pH 8.0; the optimal residence times are respectively 1 and 4 hours. Replacement of hexamethylenetetramine by formaldehyde can also be considered even if the yield is slightly lower.

Microwave-assisted synthesis of prebiotic di-D-fructose dianhydride-enriched caramels

The synthesis of prebiotic caramels involving the use of microwaves as the activating/heating source has been achieved. The yields in di-fructose dianhydrides (DFAs) in caramels were measured. The aim of this study was twofold: first to check the feasibility of the process, and second to determine the conditions to obtain an optimum response with microwave heating. The study showed that it was possible to obtain a yield of almost 50% of DFAs in a reaction time that was 10 times shorter than a previous study; i.e. 5-10 min for microwave activation compared to 60-120 min for conventional heating. It was shown that the radiation time and the radiation power were linked. The simultaneous determination of the values of these two factors was therefore necessary to obtain significant yields. This technique demonstrates the advantage of activation for mixtures such as caramels.

Synthesis and N-methylation of tetrabutylammonium isocyanurate

A simple and efficient method for the synthesis of ammonium salt of isocyanuric acid is set out. This process is based on the direct addition of the corresponding hydroxide to isocyanuric acid. This salt exhibits several interesting properties. Its alkylation by iodomethane in various solvents is demonstrated and leads to various substituted isocyanurate derivatives.

Modelling of influential parameters on a continuous evaporation process by Doehlert shells.

The modelling of the parameters that influence the continuous evaporation of an alcoholic extract was considered using Doehlert matrices. The work was performed with a wiped falling film evaporator that allowed us to study the influence of the pressure, temperature, feed flow and dry matter of the feed solution on the dry matter contents of the resulting concentrate, and the productivity of the process. The Doehlert shells were used to model the influential parameters. The pattern obtained from the experimental results was checked allowing for some dysfunction in the unit. The evaporator was modified and a new model applied; the experimental results were then in agreement with the equations. The model was finally determined and successfully checked in order to obtain an 8% dry matter concentrate with the best productivity; the results fit in with the industrial constraints of subsequent processes.

The ‘Automated Versatile Modular Reactor’:construction and use

Automation of discontinuous elementary operations specific to organic chemistry on a laboratory scale was developed as early as 1970 by the Roussel UclafCompany [1]. A modular system was chosen, because of the diversity of possible operations. Each module governs a simple operation: measuring and comparing a temperature, controlling a pump, etc. These elements communicate with one another through the on-off signal. The direction is provided by a logical programmable wired system. This modular system, Logilap (R), solves numerous problems in automation [2-4].