Red wine is a rich source of phenols with antioxidant properties that positively affect health and longevity. The antioxidants in red wine are classified into flavonoids (flavan-3-ols, anthocyanins, flavonols), phenolic acids, stilbenes, and tannins. Moderate consumption of red wine influences the cardiovascular system, exerts neuroprotective and anti-inflammatory effects, and reduces the risk of chronic diseases. However, despite these benefits, it also has drawbacks, as it contains alcohol, which is detrimental to health. Therefore, it is sensible to use dealcoholized wine for the production of polyphenol-rich dietary supplements. For the dealcoholization process, we employed solvent evaporation under reduced pressure using a rotary evaporator.
In the first part of the study, we used nuclear magnetic resonance (NMR) spectroscopy to determine the ethanol content in samples of selected wines and in samples subjected to a dealcoholization process, thereby assessing the efficiency of the dealcoholization. We also measured the ethanol content of commercially available non-alcoholic wines and compared these values with those of our partially dealcoholized samples. The commercially available non-alcoholic wines showed ethanol contents of 0.20% and 0.21% (v/v), whereas the partially dealcoholized samples ranged from 1.72% (Merlot) to 6.44% (v/v) (L’Abbaye Chinon). The NMR results indicated a systematic positive bias, as the method consistently overestimated the values. We found that dealcoholizing 150 g of wine at 40 °C and a reduced pressure of 40 mbar for two hours did not achieve the target ethanol content of below 0.50% (v/v); the Cabernet sample (VinaKoper) retained an ethanol content of 0.99% (v/v) after the process. The partially dealcoholized samples were stored in the dark, and we monitored changes in pH—an indicator of quality alteration—over a 30-day period. We found no significant change in pH. Subsequently, we determined the Total Polyphenol Index (TPI) and the Total Polyphenol Content (TPC), the latter expressed as gallic acid equivalents per liter. Based on the evaluated parameters, the most suitable wine sample was Refošk (VinaKoper), with high TPI (81.5) and TPC (3256 mg GAE/L) values, indicating the highest polyphenol content. The other wines had TPI values ranging from 37 to 80 and TPC values between 1900 and 2800 mg GAE/L.
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