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Biomedical subjects

F Grivel

Publications and source records attributed to F Grivel.

6 recordsLinked to original sources
PubMed2001

Phase transfer and biocatalyst behaviour during biotransformation of beta-ionone in a two-phase liquid system by immobilised Aspergillus niger.

The biotransformation of beta-ionone by Aspergillus niger IFO 8541 entrapped in Ca-alginate beads was investigated in a two-phase liquid system, due to the low aqueous solubility of the precursor. Modelling of phase transfer processes of the substrate demonstrated that the solute was transferred from the organic droplets to the gas, giving a loss by stripping, and then from the gas to the aqueous solution where a chemical degradation occurred. The biological reaction took place after direct precursor transfer from the organic layer to the biocatalyst by surface adsorption. Studies on the biological process demonstrated the critical effect of the biomass content in the medium at the time at which beta-ionone was added. Optimum conditions involved fed-batch feedings of both precursor and carbon source (sucrose) after the biomass concentration reached a value close to 6.8g/l. The biotransformation process then took place at a constant rate of 0.046mmol/lh with a reaction yield, defined with respect to beta-ionone metabolised by the fungus, close to unity. Best results achieved in this study allowed to obtain 3.5g/l biological compounds after 400h reaction.

Journal Article↗
PubMed1999

Determination of the reaction yield during biotransformation of the volatile and chemically unstable compound beta-ionone by aspergillus niger

Biotransformation of beta-ionone by Aspergillus niger IFO 8541 was a complex system, due to the low precursor solubility in water (0.88 mol/m(3)) which gave a two-phase liquid system, its high volatility (vapor pressure 7.2 Pa), and its poor chemical stability. A dynamic model, considering transfers between organic, aqueous, and gas layers, was established. It also took into account the decrease in organic layer area exchange during a process, due to progressive precursor disappearance. Its solving needed separate determination of two parameters. The first-order kinetic constant for chemical degradation, K(1), was estimated from side experiments involving a model system at thermodynamic equilibrium; its value was found to be close to 4.17 x 10(-)(6) s(-)(1). The volumetric transfer coefficient between gas and aqueous phase was estimated by analogy with results obtained for oxygen transfer. Results obtained demonstrated high liquid-gas transfer rates, while liquid-liquid transfers were severely limited. These data were then used to estimate the true yield of a biotransformation experiment, which was found to be close to unity.

Journal Article↗
PubMed1991

Ambient temperatures preferred by young European males and females at rest.

Forty-eight young adults (24 men and 24 women) stayed for three hours in a climatic chamber setting, lightly clothed and seated at rest with no prescribed task; rectal and mean skin temperatures were continuously recorded. During the first hour, the subjects were exposed to an imposed ambient temperature (25.1 degrees C) during which body temperatures stabilized and subjective thermal judgments were collected. For the next two hours they could freely set the ambient temperature at the level(s) they preferred. The subjects spent about one hour seeking a preferred temperature (transition period), which subsequently turned out to be unsteady in most cases. The overall mean of the individual average preferred temperatures (third hour) was 26.6 degrees C (S.D. = 2.6 degrees C). Significant time of day (morning versus afternoon) effects were found on preferred ambient and actual body temperatures. The body temperatures previously recorded at 25.1 degrees C were significantly predictive of the average ambient temperatures preferred between one and two hours later (third hour); the multiple regression equations differed markedly between men and women.

Adult↗
PubMed1989

Mean skin temperature in warm humid climates.

Mean skin temperature (Tsk) was measured in 24 subjects during experiments in a climatic chamber. Three conditions of ambient temperature (Ta = 25.6 degrees, 28.9 degrees and 32.2 degrees C), and three of humidity (relative humidity = 50%, 70% and 90%) were studied. A relationship was established by a linear regression technique. It is valid in the 24 degree-34 degree C range, for air velocity = 0.2 m.s-1, clothing insulation = 0.077 degrees C.m2.w-1 (0.5 clo), metabolic rate = 64 w.m-2 (1.1 met) and radiant temperature = air temperature. In these conditions Tsk = 28.125 + 0.021 Pw + 0.210 Ta (Pw: ambient water vapour pressure in mb). It shows a small humidity influence. The influences of sex, transition from one condition to the next, and air velocity were also studied. Measurements in Africa confirmed the small influence of humidity. Ethnic life-style differences indicated that a high precision in Tsk determination is difficult to achieve.

Adult↗