Mathematical modeling of fermentation kinetics: a tool to better understand interactions between Torulaspora delbrueckii and Saccharomyces cerevisiae in mixed cultures

Abstract

Nowadays the use of Torulaspora delbrueckii is more and more common in winemaking. However, its behavior in presence of Saccharomyces cerevisiae is not always predictable. Indeed, the interactions existing between the two yeasts are still not well characterized and can lead to a bad control during their implementation in mixed cultures. The objective of the work presented here was to use the mathematical modeling as a tool to better understand microbial interactions in this context. 

Mixed cultures of a couple of oenological yeasts composed of T. delbrueckii and S. cerevisiae were carried out on a synthetic grape must in anaerobiosis. The impact of various parameters was evaluated: assimilable nitrogen concentration, direct and indirect contact (thanks to a membrane bioreactor), increase of lipids concentration (Tween 80 and ergosterol). 

The analysis of experimental data acquired during the pure cultures of each yeast enable to establish a mathematical model to describe the fermentation kinetics for pure cultures. Then this model was used to predict the kinetics of mixed cultures without any interaction except competition for substrates (sugar and nitrogen). The comparison between predicted and experimental kinetics showed that in mixed culture several kind of interactions must be taken into account: competition for space, cell to cell contact, reciprocal stimulation. Moreover, at low lipids initial concentration, S. cerevisiae dominated T. delbrueckii by producing a toxic metabolite. An increase in the initial lipids concentration completely reversed this domination.