Nitrogen utilisation of selected non-Saccharomyces yeasts and the impact on volatile compound production

[摘要] ENGLISH ABSTRACT: During fermentation, nitrogenous compounds serve as nutrients for the yeasts, which enabletheir growth, functioning and maintenance of the yeasts cells. From a winemaking perspective,a certain amount of nitrogen is required for the yeasts in order to avoid sluggish or stuckfermentation. Moreover, nitrogen metabolism leads to the production of aroma compounds suchas higher alcohols, fatty acids and esters which contribute positively to overall sensorycharacteristics of wine. Nitrogen metabolism (uptake of ammonium and amino acids) have beenextensively studied in Saccharomyces cerevisiae. Nonetheless, the fairly great variancesobserved between strains in terms of preference for certain nitrogen sources and metabolismthereof are not so well understood. Additionally, these mechanisms nitrogen metabolism of non-Saccharomyces yeasts are even vaguer and simply assumed to be globally similar to those ofS. cerevisiae.This study aimed to investigate the uptake of nitrogen compounds (ammonium and individualamino acids) by selected non-Saccharomyces yeasts (Lachancea thermotolerans IWBT Y1240,Torulaspora delbrueckii Biodiva TD291, Pichia kluyveri FrootZen, Metschnikowia pulcherrimaIWBT Y1123 and Metschnikowia pulcherrima Flavia) to assess the impact of fermentationkinetics and the production of aroma compounds during sequential fermentations with S.cerevisiae under different initial YAN concentrations, with 300 mg/L, 150 mg/L and 75 mg/L,respectively). Fermentations were performed in a synthetic grape juice medium with pure andsequential fermentations. The data showed that the assimilation of nitrogen compounds werespecies specific. For example, L. thermotolerans preferred alpha amino nitrogen aboveammonia, where the opposite hold true for T. delbrueckii. Notable differences could also beidentified for the uptake of certain single amino acids. Irrespective of the initial YANconcentrations during sequential fermentations, the yeasts only assimilated about half of theinitial YAN. The non-Saccharomyces yeasts did not influence fermentation performance duringsequential fermentations. However, a low initial YAN (75 mg/L) had a strong influence on thefermentation kinetics and aroma compound production. The higher uptake (compare to S.cerevisiae) of specific single amino acids by non-Saccharomyces yeasts (especially L.thermotolerans), can be tentatively correlated with certain aroma compounds produced at theend of fermentation. The results also revealed that agitation could impact overall fermentationperformance and aroma compound production. This study contributes to an improvedunderstanding of how different initial nitrogen concentrations affect growth, fermentationperformances and aroma compound production of wine-related yeasts under fermentativeconditions. Moreover, the uptake of single amino acids by selected non-Saccharomyces yeastshad also been identified, which is a good starting point to better understand non-Saccharomyces yeasts nitrogen requirements which may be used for the optimization ofnitrogen source addition, during alcoholic fermentation, when used in mixed fermentations inorder to ensure a complete alcoholic fermentation. To the best of our knowledge, the uptake ofsingle amino acids and YAN consumption by selected non-Saccharomyces yeasts underfermentation conditions tested, have never been studied before.

[发布机构] Stellenbosch University