The impact of nutrients on aroma and flavour production during wine fermentation

[摘要] ENGLISH ABSTRACT: During wine fermentation, numerous grape must constituents serve as nutrients to wine yeast(Saccharomyces cerevisiae), which enable their growth and successful completion of alcoholicfermentation. Many of these nutritional factors, in particular nitrogen, also act as precursors for yeastderivedflavour compounds such as higher alcohols, esters and volatile fatty acids. Yeast nitrogenmetabolism thus plays a determining role in wine aroma and quality. Not only is the nitrogen source,concentration and supplementation timing important, but various environmental factors and the geneticconstitution of the yeast strain used for fermentation will also contribute to fermentation outcomes.The main goal of this work was to explore the complex interactions between a number of contributingfactors; namely nitrogen source, timing of addition, yeast strain and fermentation matrix. Broadly, thisstudy assessed the impact of seven different nitrogen combinations, added either to the initial grape mustor after the onset of fermentation, on fermentation performance and aroma compound production by ninecommercial wine yeast strains. Fermentations were done in synthetic grape must, and validated for asubset of parameters in real grape must. The nitrogen treatments were designed according to the generallyestablished order of preference of S. cerevisiae for individual amino acids as source of nitrogen underfermentative conditions, and the potential of certain amino acids to participate in metabolic pathways thatproduce specific aroma compounds.The results reveal that different nitrogen combinations can lead to unexpected aroma outcomes,depending strongly on the genetic background of individual yeast strains and the timing of nitrogenaddition. Certain nitrogen treatments consistently resulted in significant increases or decreases in specificaroma compound concentrations in comparison to the treatment fermented on ammonium as onlynitrogen source, for multiple yeast strains. These compounds were classified as nitrogen treatmentdependent. Other aroma compounds were produced similarly for all nitrogen treatments and weredesignated as nitrogen treatment independent. The presence of specific amino acid groups (for examplethe branched-chain and aromatic amino acids) could be correlated to significantly altered productionpatterns of related (such as higher alcohols) or unrelated (diethyl succinate) aroma compounds relative tothe other nitrogen treatments. Taken together, a number of interesting and novel hypotheses regarding themetabolic pathways involved could be derived from the data.Ultimately, this initial assessment of interactive effects during fermentation will contribute to practicalguidelines for winemakers to allow matching grape must constituents (such as nutrients) with the intrinsicaroma production capabilities of specific yeast strains in order to modulate wine aroma, style and quality.

[发布机构] Stellenbosch University