Polyphenolic Profile, Antioxidant, Antibacterial and Antidiabetic Activities of Acorns from Three Tunisian Quercus L. Species

This study aims to evaluate the interspecific variation in polyphenolic profiles and biological activities of acorn flours from three native Tunisian <i>Quercus</i> L. species (<i>Q. ilex</i> L., <i>Q. suber</i> L., and <i>Q. canariensis</i> Willd.). <i>Q. canariensis</i> extracts are the richest in total phenolic, flavonoid and hydrolysable tannin contents. Six phenolic compounds were identified by HPLC-DAD analysis. Chlorogenic acid was the dominant compound in <i>Q. canariensis</i> and <i>Q. ilex</i> acorns. Whereas in <i>Q. suber</i>, caffeic acid was the main component and, along with trans-ferulic acid, was exclusive to this species. Hyperoside was notably identified in <i>Q. canariensis</i>. The UHPLC-DAD-MS analysis of hydrolysable tannins revealed twelve compounds. Acorns of <i>Q. canariensis</i> and <i>Q. suber</i> were dominated by ellagitannins, whereas <i>Q. ilex</i> contained mainly gallotannins. To our knowledge, these compounds are identified for the first time in Tunisian acorns. <i>Q. canariensis</i> exhibited the strongest antioxidant potential with DPPH, ABTS and FRAP assays, as well as the highest antibiofilm and anti-α-amylase activities. All extracts inhibited ATCC pathogenic bacterial strains while largely sparing the beneficial probiotic <i>Limosilactobacillus fermentum</i>. This result indicates a selective antibacterial effect not previously reported for <i>Quercus</i> acorns. <i>Q. canariensis</i> may represent a potential source of functional food ingredient, nutraceuticals, and pharmaceuticals, which remains to be confirmed through <i>in vivo</i> investigations.