Formation of Phenethyl Alcohol and Tyrosol during Fermentation of a Synthetic Medium lacking Amino-acids

Modelling the physiological status of yeast during wine fermentation enables the prediction of secondary metabolism

Saccharomyces non-cerevisiae yeasts are gaining momentum in wine fermentation due to their potential to reduce ethanol content and achieve attractive aroma profiles. However, the design of the fermentation process for new species requires intensive experimentation. The use of mechanistic models could automate process design, yet to date, most fermentation models have focused on primary metabolism. Therefore, these models do not provide insight into the production of secondary metabolites essential for wine quality, such as aromas. In this work, we formulate a continuous model that accounts for the physiological status of yeast, that is, exponential growth, growth under nitrogen starvation and transition to stationary or decay phases. To do so, we assumed that nitrogen starvation is associated with carbohydrate accumulation and the induction of a set of transcriptional changes associated with the stationary phase. The model accurately described the dynamics of time series data for biomass and primary and secondary metabolites obtained for various yeast species in single culture fermentations. We also used the proposed model to explore different process designs, showing how the addition of nitrogen could affect the aromatic profile of wine. This study underlines the potential of incorporating yeast physiology into batch fermentation modelling and provides a new means of automating process design.

Histaminol: identification and HPLC analysis of a novel compound in wine

Histaminol, a minor histamine metabolite originating from imidazole acetaldehyde, has been detected in a food matrix as complex as wine. The standard molecule was synthesized, and subsequently the chemical structure was confirmed by ESI-MS and NMR measurements. The development, optimization, and in-house validation of a HPLC-DAD chromatographic method for the quantitative determination of histaminol in wine are described and discussed. The expanded uncertainty (U(k=2)) of the procedure was estimated as 11.06%. Twenty commercial Italian wine samples were selected. All samples (16 red and 4 white wines) were analyzed after a C-18 SPE cartridge fractionation procedure. The content of this alcohol was in the range of 0.289-1.094 mg/L (minimum and maximum values were obtained for Nero d'Avola vintage 2007 and Barolo vintage 1969, respectively).