Effect of nitrogen addition on cellular physiology of yeast during alcoholic fermentation

Abstract

Assimilable nitrogen is essential for yeast metabolism and growth. Nitrogen limitation is one of the most common causes for stuck and/or sluggish fermentation in winemaking. To prevent these problems, a common practice is to supplement the grape juice with ammonium salts, preferably at early stages of alcoholic fermentation. The effect of these additions has been studied during the last decades from several points of view (Bell and Henschke 2005). However, a comprehensive description about the effects of nitrogen supplementation on cellular physiology (growth rates, substrate consumption rates, products release rates...) along the whole fermentation process has not been reported yet. These kind of studies could be the key for studying nitrogen supplementation from a metabolomic and/or fluxomic point of view. The aim of this work is to provide a detailed analysis and characterization of yeast cellular physiology during the alcoholic fermentation of synthetic must presenting different nitrogen supplementation. On one hand, a poor nitrogen must (containing 100 mg/L of yeast assimilable nitrogen -YAN-) has been supplemented up to the ideal nitrogen content (200 mg/L of YAN for 240 g/L of sugar content). On the other hand, a must presenting an ideal nitrogen content has been over-supplemented with 300 mg/L of YAN. These batch cultures were performed in triplicate in a DasGip parallel bioreactor system. Differences on the production of organic acids (especially acetic acid ) and aromatic profile have been observed at the end of the fermentations depending on timing of supplementation and the amount of nitrogen added. Furthermore, this work provides the basis for further studies in metabolic flux distribution of yeast growing under these conditions.