Study of the impact of nitrogen additions and isothermal temperature on aroma production in oenological fermentation

Abstract

Nitrogen and temperature are two important factors that influence wine fermentation and volatile compounds production. Among the different compounds present in the must, nitrogen is an essential nutrient for the management of the fermentation kinetics but it also plays an important role in the synthesis of fermentative aromas. To address the problems related to nitrogen deficiencies, nitrogen additions during alcoholic fermentation have been developed. The consequences of such additions on the main metabolism are well known. However, their impact on the synthesis of aromas has been poorly understood. Fermentation temperature is another variable that affects the production of fermentative aromas in wine. For example, high concentrations of esters are obtained at low temperatures whereas higher alcohols are obtained at high temperature. Nevertheless, the impact of fermentation temperature on aroma production kinetics has never been studied in interaction with nitrogen addition during fermentation.So, the main objective of this study was to evaluate the impact of nitrogen addition at different fermentation temperature on both the fermentation kinetics and aroma synthesis kinetics thanks to online GC-MS system. We also studied the effect of the initial nitrogen content of the must and the quantity of added nitrogen. To study the impact of these 3 parameters simultaneously, we used a Box-Behnken design with response surface modeling and GAM modeling.Our results indicated that all three factors studied had important effects on fermentation and aroma production kinetics. These parameters do not impact in the same way the different families of volatile compounds. For example, high temperatures induce an important evaporation for ethyl esters and isoamyl acetate, while an increase in the production of isobutyl acetate is observed when the temperature increase. Moreover, the study of these three factors simultaneously allowed us to show that propanol is not only a marker of the presence of assimilable nitrogen in the medium, but above all a marker of cellular activity.This work enables to get a deeper understanding of the regulation of the yeast metabolism. It also underlines the possibility to refine the organoleptic profile of a wine by targeting the ideal combination of initial and added nitrogen concentration and fermentation temperature.