Geraniol is the main monoterpenic alcohol of some red grapes occurring both in the free form (aromatic) and in the glycosilated (neutral) form. Free geraniol is transformed into other terpenic compounds (linalool and α-terpineol) through acid hydrolysis. During fermentation, yeasts also change must free geraniol into citronellol. The final aroma of wines is mainly due to both the unchanged geraniol and the formed citronellol, thus the key role played by yeasts in the vinification of those aromatic wines is proved. In the present work the metabolism towards geraniol of 5 different strains of S. cerevisiae were studied. The laboratory tests were carried out using a must from neutral grapes as the fermentation medium. Two different amounts of geraniol were added to the medium to evaluate the influence, if any, of the initial concentration of monoterpenic alcohol on the transformation rate of this compound. At different stages of fermentation geraniol and citronellol, as well as other terpenic compounds, were evaluated by means of GC on samples extracted by SPE on a C18 cartridge.
The results proved that the yeast strain dramatically affects the amount of both geraniol and citronellol occurring in the medium at the end of fermentation. Therefore in the fermentation of aromatic musts in which geraniol is the main component, the choice of the yeast proves decisive for the quality of wines.
The influence of tween 80, added to the medium as a source of oleic acid, on the biosynthesis of citronellol was evaluated as well. The results showed that tween 80 increases the production of citronellol, though no remarkable changes in the consumption of geraniol were observed. It can therefore be concluded that the production of citronellol by yeasts is a minor way of utilizing geraniol when no longer needed for the synthesis of cell fats.
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