Influence de la température sur la cinétique, de croissance et le coefficient de maintenance de Candida lipolytica cultivé sur n-alcane

Abstract

The effect of growth temperature on the evolution of kinetic parameters and yields was determined for Candida lipolytica cultures with ntetradecane as substrate, in a temperature range of 18°C to 30°C, which is below the critical growth temperature in order to work only in the activation zone of these parameters.

In such a culture limited by substrate transfer, growth rate depends on biological rates, related to microorganisms characteristics, and diffusional rates, related to mass transfer. The effect of temperature thus depends on the limiting step. The activation energy, calculated from exponential growth rate determinations is $E_{\mu _m } = 63,600{\text{ }}J/mole$.

When the activation energy is calculated from the maximal rate of cell production (determined at the growth curve's inflexion point), it's found to be E _μX=71,200 J/mole in the 18°C–24°C range, and E _μX=28,000 J/mole in the 24°C–30°C range. The latter one is characteristic of a diffusion-limited process. Above 24°C, growth is controlled by substrate-transfer, as physiological potentialities are preferentially increased with temperature than diffusional ones: 24°C is thus the transition temperature T _t from physiological to diffusional limitation.

The apparent yield is almost constant, over the 18°C to 30°C temperature range, although maintenance coefficients are very dependent on temperature. The activation energies related to maintenance coefficients for alkane and oxygen respectively are $E_{m_s } = 82,500{\text{ }}J/mole$ and $E_{mO_{\text{2}} } = 86,200{\text{ }}J/mole$.

The m _s/m_{O 2} ratio is about 3 (g/g), whereas that, for a strict oxidation reaction of n-tetradecane ought to be 3.47 (g/g). A satisfactory correlation, relating maintenance coefficients to the maximal growth rate of yeast, is given.