## 1 Introduction
According to their origin, volatile compounds are often classified into varietal, fermentation, and aging aromas [20]. Varietal aroma compounds derive from grapes and are later transformed during pre-fermentation processes and fermentation. This class includes mainly terpenoids and norisoprenoids, while certain grape cultivars may also contain significant amounts of thiols and methoxypyrazines. The fermentation process yields numerous compounds, with a key impact on the aroma of all wines in general, including higher alcohols, fatty acids, and especially esters. Besides modulating the initial composition, the wine-aging process can produce particular other compounds and, in this way, further affect the volatile profile of wine. Several studies showed significant effects of the use of _L. thermotolerans_ in fermentation on volatile aroma profile of wine, with strain-specific impacts, as well as the impact of inoculation timing. For example, in sequential fermentation, this species was shown to be able to increase the levels of particular higher alcohols and esters and decrease aldehydes and certain fatty acids [21]. [PERSON] et al. [12] reported about higher production of isobutyric acid and ethyl esters in wines produced by sequentially inoculated _L. thermotolerans_, the same as [PERSON] et al. [19] and [PERSON] et al. [17] observed for ethyl lactate and isobutanol, respectively, and [PERSON] et al. [22] for 1-propanol. Despite several valuable reports, the aromatic potential of _L. thermotolerans_ has still not been distinguished well, probably because of the limited number of aromatic compounds that can be determined by conventional analytical techniques which have been mostly used in studies so far. In this way, many potentially important effects and compounds remained undiscovered. In this study, together with conventional gas chromatographic techniques, comprehensive untargeted two-dimensional gas chromatography with time-of-flight mass spectrometry (GC\(\times\)GC/TOF-MS) was used to analyze the volatile aroma potential of _L. thermotolerans_ in detail and compare it with that of an _S. cerevisiae_ control. Two gas chromatographic columns with stationary phases of different polarity and different lengths were used, connected with a modulator which transfers the effluent from a primary column to additional separation in a shorter secondary column. Application of this technique results in mass spectra without interference and enhanced sensitivity and, consequently, a much larger number of identified volatile compounds [23; 24]. Besides volatile compounds, this study addressed the repercussions of fermentation with _L. thermotolerans_ on other important wine components, such as phenols and pathogenesis-related proteins which were investigated from this aspect poorly [25] or not at all up to date, respectively. The aim of this study was to significantly deepen the level of knowledge about the influence of co-fermentation with _Lachancea thermotolerans_ on the chemical composition of white wine. In addition to basic physico-chemical parameters and evaluation of sensory quality, the focus was especially directed towards detailed characterization of the composition of volatile aroma compounds using the currently most advanced analytical techniques, such as GC\(\times\)GC/TOF-MS, as well as towards the first findings on the influence of _L. thermotolerans_ on phenols and proteins originating from grapes. The experiment was performed with Malvazija istarska (_Vitis vinifera_ L.) white grape must, which, in certain terroirs and growing seasons, results in wines with low acidity and high alcohol content, so the results may also have a practical significance.