Kinetic analysis and gas-liquid balances of the production of fermentative aromas during winemaking fermentations: Effect of assimilable nitrogen and temperature

- Dynamic gas-liquid balance of the main higher alcohols and esters
- Differentiation between biological and physical consequences of temperature
- Assimilable nitrogen: major factor affecting the production kinetics of volatiles
- Propanol synthesis strictly correlated to intracellular nitrogen availability
- For each aroma, two linear phases of production depending on sugar consumption

The impact of temperature and assimilable nitrogen on synthesis of the principal fermentative aromas by yeasts was evaluated with an online GC system. Kinetic parameters and gas-liquid balances were precisely calculated, making it possible to differentiate between the biological and physical consequences of temperature shifts. The lower liquid concentrations of esters at high temperature resulted mostly from large losses by evaporation, with only limited changes in yeast metabolism. Nitrogen availability was the main fermentation parameter affecting the kinetics of higher alcohol and ester synthesis, but the magnitude of this effect depended on temperature. The production of fermentative aromas was closely linked to central carbon metabolism, except for propanol. Indeed, two successive linear production phases (with yields dependent on initial nitrogen content and temperature) were obtained when volatile compound synthesis was plotted against sugar consumption. Overall and specific rates of isobutanol and isoamyl alcohol production were affected differently by nitrogen and temperature, indicating major differences in the regulation of synthesis for these two compounds, despite their partially shared metabolic pathways. Finally, propanol was produced exclusively during the nitrogen consumption phase, and the amount produced increased with initial nitrogen concentration. This compound was, therefore, identified as a quantitative, metabolic marker of the availability of intracellular nitrogen.