May Sulfites in Wine Affect Gut Microbiota? An In Vitro Study of Their Digestion and Interplay with Wine Polyphenols

Sulfites are widely used in the wine industry, but their human health effects remain debated. This study is the first to investigate the interaction between wine sulfites and gut microbiota under simulated gastrointestinal conditions. Using the simgi model, red and synthetic wines─with and without SO₂ (200 mg/L)─underwent gastrointestinal digestion and colonic fermentation with fecal microbiota from three healthy donors (n = 3). SO₂-treated wines slightly modified gut microbiota composition, decreasing beneficial bacteria like Bacteroides and Ruminococcus, while increasing Coprococcus and pro-inflammatory Escherichia/Shigella, although the overall microbiome of each individual seems to condition its resilience toward SO₂. These effects were partially mitigated in red wine, suggesting a protective role of wine polyphenols. Additionally, SO₂ treatment in red wines enhanced phenolic metabolism at the gut level, increasing low-molecular-weight phenolic compounds, such as valerolactones, bioavailable in the small intestine and colon. For instance, 5-(3′,4′-dihydroxyphenyl)-γ-valerolactone concentrations were consistently higher in SO₂-treated red wine (0.86–1.28 mg/L) than in the untreated wine (<0.78 mg/L) after 6 h of fermentation. This pioneering study reveals a complex interplay between sulfites, wine components, and gut microbiota, with potential health implications, especially for sulfite-sensitive individuals.