engleski

Early fermentation aroma profiles of grape must produced by various non-Saccharomyces starters

Saccharomyces cerevisiae is the most commonly used yeast species in winemaking. The recent research showed that non-Saccharomyces yeasts as fermentation starters show numerous beneficial features and can be utilized to reduce wine alcoholic strength, regulate acidity, serve as bioprotectants, and finally improve wine aromatic complexity. The majority of published studies on this topic investigated the influence of sequential or co-inoculations of non-Saccharomyces and S. cerevisiae yeasts on the aroma of final wine. Although some results are consistent with each other, there are many contrasting and contradicting outcomes, which most likely derived from the differences in grape juice composition, as well as due to various combinations and interactions of non-Saccharomyces and S. cerevisiae strains used in different studies. For these reasons, the actual contribution of non- Saccharomyces yeasts was often not completely distinguishable. The main premise of this study was that by investigating the production of volatile aroma compounds produced by non- Saccharomyces yeasts in the early phase of fermentation, prior to interaction with S. cerevisiae, a valuable insight from another perspective can be achieved about the particular effects they induce. Malvazija istarska (Vitis vinifera L.) white grape must was inoculated with the following non-Saccharomyces yeasts: Torulaspora delbrueckii, Metschnikowia pulcherrima, Pichia kluyveri, Lachancea thermotolerans and Schizosaccharomyces pombe, while Saccharomyces cerevisiae was used as a control. The fermenting grape musts were subjected to headspace solid-phase microextraction and gas- chromatography-mass spectrometric analysis at the point just before S. cerevisiae inoculation, when alcohol level reached 1.5 – 2.5 vol. %. Each of the investigated non-Saccharomyces yeasts produced a unique and distinctive aroma profile. The highest concentrations of linalool and β- damascenone were found in the must fermented by Pichia kluyveri and the lowest in the control S. cerevisiae must. The concentration of 2- phenylethanol produced by S. cerevisiae almost doubled those found in the musts of non- Saccharomyces starters. Ethyl propanoate differentiated well the investigated yeasts, with the highest concentration found in T. delbrueckii must. This must also contained the highest concentrations of some other propanoates, including 2-phenethyl propanoate which turned out to be specific for this species. Particular non- Saccharomyces yeasts boosted the early synthesis of many important esters, such as ethyl hexanoate, ethyl octanoate and 2-phenethyl acetate, the main contributors to fruity and flowery notes of wine aroma. The obtained results showed that the potential of the investigated non-Saccharomyces yeasts to produce diverse wines is rather high. This study was funded by Croatian Science Foundation under the projects IP-2020-02-4551 and DOK-2021-02-5500.

non-Saccharomyces yeasts, sequential inoculation, SPME-GC-MS, volatile aroma compounds, esters

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