Oak (Quercus aegilops L.) Root Bark Tannins Astringency, Antioxidant Potential, and Use as Functional Tea

Tannins from the root bark of Quercus aegilops L. were extracted in two successive seasons and their astringency score and antioxidant potential were evaluated using bovine serum albumin (BSA) radial diffusion and 2,2- Diphenyl – 1-Picrylhydrazyl  (DPPH) assay methods respectively. The results revealed that the root bark of this oak species contained on average 11.39 %( w/w) tannins as gallic acid, of which about  79%  are hydrolyzable ( HT) and 21%  condensed (CT) tannins with the former composed mainly of ellagitannins and much fewer gallotannins and free gallic acid. The results also revealed that the crude root bark powder and its purified tannins have astringency scores of 15.8 and 138.98 mg BSA/g respectively. The antioxidant potential was evaluated by DPPH assay and expressed as inhibition capacity (IC50) was 149.7 ppm and 19.24 ppm for the crude bark powder and its purified tannins respectively indicating the superior antioxidant potential of these tannins to that of ascorbic acid. The highly-antioxidant functional tea prepared from these tannins was clear and acceptable to tasters.