Modelling of <em>S. cerevisiae</em> and <em>T. delbrueckii</em> pure culture fermentation in synthetic media using a compartmental nitrogen model

Abstract

Aim: The objective of the present work is to propose a model describing the evolution of the pure culture fermentation of two oenological yeasts: S. cerevisiae and T. delbrueckii.Methods and results: For both yeasts, pure culture fermentation was performed in a synthetic medium with different initial concentrations of yeast available nitrogen. The datasets obtained from those experiments were used to identify the parameters of the proposed model.Conclusions: The developed comprehensive model of wine-making fermentation is based on the partition of assimilated nitrogen between the constitutive and the storage compartments. It efficiently describes the evolution of S. cerevisiae and T. delbrueckii pure cultures. This mass-balance model provides a stoichiometric approach in biomass production, unlike nitrogen backboned models used in winemaking. Moreover, it gives an estimation of non-accessed data such as nitrogen partition between vacuole and cytosol during T. delbrueckii fermentation.Significance and impact of the study: The developed model is robust enough to precisely describe the fermentation evolution of two pure culture yeasts and therefore has future potential for modelling mixed culture fermentations of S. cerevisiae and T. delbrueckii.

Modelling the effects of assimilable nitrogen addition on fermentation in oenological conditions

“…Assuming a constant yield of CO2 released and ethanol produced during fermentation, the ethanol and CO2 productions rates are described by Eq (11) and ( 12):…”

“…gS is slightly lower than 2 mol/mol, the theoretical yield of ethanol production, because sugar is also converted into other metabolites like glycerol and aromas. The biomass composition is taken from [11].…”

“…with X the biomass concentration in 10 9 cell/L. The value of 𝑎 and MX are those of Brou's model [11]: 37.6 10 9 cell/g and 25.0689g/C-mol respectively.…”

“…David et al [10] shows that residual growth is observed after the total consumption of nitrogen present initially in the medium which would suggest that the yeasts have a nitrogen reserve to continue their growth. Brou et al [11] shows that intracellular nitrogen concentration decreases to a minimum during fermentation. It is therefore important to consider the intracellular nitrogen concentration in the yeasts.…”

“…Ethanol and CO2 are produced from sugar in an overall yield (1 gram of sugar is converted into 2.17 grams of ethanol and 2.17 grams of CO2).  Brou's model [11] is based on an intracellular nitrogen compartment divided between the minimum nitrogen necessary to carry out the vital functions of the cells and a storage compartment, which is the only nitrogen available for biomass growth. It considers ethanol inhibition on metabolism of yeasts (production of biomass, ethanol and glycerol) as well as the cell death rate function of ethanol concentration.…”