Despite the wide literature describing the biological effects of polyphenols, scarce data are available on their content in the human diet. This study examined total polyphenols content, free and total phenolic acids profile, and antioxidant activity of different commercial beers types (abbey, ale, bock, wheat, lager, pilsner, and dealcoholized). Ferulic acid is by far the most abundant phenolic acid in beers, followed by sinapic, vanillic, caffeic, p-coumaric, and 4-hydroxyphenylacetic acids. Ferulic, caffeic, syringic, sinapic, and, to a lesser extent, vanillic acids are present in beers mainly as bound forms, whereas p-coumaric and 4-hydroxyphenylacetic acids are generally present equally in free and bound forms. Total polyphenols and phenolic acids contents greatly vary among different beer types (i.e., total polyphenols, from 366 μg/mL gallic acid equivalents for dealcoholized beers to 875 μg/mL gallic acid equivalents for bock beers, with higher values measured in bock, abbey, and ale beers and lower values in dealcoholized beers). Similarly, the antioxidant activity measured with the ferric reducing antioxidant power (FRAP) assay is remarkably different depending on beer type (from 1525 μM for dealcoholized beers to 4663 μM for bock beers), with higher values in bock, abbey, and ale beers and lower values in dealcoholized beers. FRAP values strictly correlate with polyphenols and phenolic acids content. The contribution of single phenolic acids to the antioxidant activity measured with FRAP assay was also studied.

Despite the vast literature describing the biological effects of phenolic compounds, rather scarce data are available on their absorption from diet in humans. The present study focused on the absorption in humans of phenolic acids from white wine, particularly hydroxycinnamic acids and their esters with tartaric acid. The results obtained indicate that, following a single wine drink, hydroxycinnamic acids from white wine are absorbed from the gastrointestinal tract and circulate in the blood after being largely metabolized to the form of glucuronide and sulfate conjugates. Unmodified tartaric acid esters of hydroxycinnamic acids from wine are present in human plasma at low levels, if any. Wine hydroxycinnamic acids, although present in wine as conjugated forms, are still bioavailable to humans.