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Background and Aims: Wines aged in wood barrels are likely to contain Brettanomyces yeasts, which are able to produce off-flavour compounds such as ethylphenols and vinylphenols. In this work, both off-flavoured and pleasant phenol compounds were quantified in Portuguese wines with an improved analytical technology. Methods and Results: A novel one-step dispersive liquid-liquid microextraction method with simultaneous derivatisation followed by fast low-pressure GC/MS was optimised and applied to 49 red wine samples of commercial and private origin. The analytical performance demonstrated the ability of the proposed method to accurately measure all the analytes under study.Conclusions: Ethyl and vinylphenols were present in most of the wines, at a concentration frequently higher than their preference threshold, and thus high enough to affect the overall aroma of the wine. Home-made wines had a higher concentration of off-flavour compounds in contrast with that of commercial wines, which had a high concentration of pleasant flavour compounds. Statistical analysis showed that less expensive wines exhibited a significantly lower concentration of syringol, and there was a tendency for the concentration of vinylphenols and ethylphenols to increase throughout wine aging.Significance of the Study: The presence of off-flavour phenols is a major concern of the wine industry, requiring great attention during the different stages of the winemaking process, so that wine aroma is not negatively affected. Figure 1. Formation of ethylphenols from hydroxycinnamic acids: A two-step reaction, adapted from Carrillo and Tena (2007) and Kheir et al. (2013).

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