| Popis: |
Photometric, chromatographic and electrochemical techniques were employed to examine the total phenol (TP) content, polyphenolic composition and antioxidant capacity (AC) of ten commercial fruit teas: blueberry, tangerine/peach, pomegranate, apple, grapefruit, wild berry, orange, apricot, cherry and strawberry. The TP content determined according to the Folin-Ciocalteu assay (FC) ranged from 323 mg/L (grapefruit) to 1549 mg/L (pomegranate) gallic acid equivalents (GAE). Only pomegranate, apricot, and strawberry teas exhibited TP content greater than 1 g/L GAE. Individual phenolic composition of teas was determined using HPLC. Epigallocatechin gallate (EGCG) and chlorogenic acid were detected in all tested teas at appreciable concentrations, up to 161 mg/L (pomegranate) and 78 mg/L (strawberry), respectively. In addition, catechin, protocatechuic and cinammic acids were identified in approximately half of the tested teas. Cyclic voltammetry at a glassy carbon electrode and potentiometric titration at a platinum electrode were employed to elucidate the AC of tested teas. AC derived from potentiometric titration curves and expressed in ascorbic acid equivalents (AAE) resulted in separation of teas into the high and low antioxidant concentration groups, with pomegranate (334 μ M AAE), apricot (63 μ M), and strawberry (64 μ M) teas having the highest AAE values, and the remaining teas exhibiting AAE << 20 μ M. The charge passed to 600 mV, Q600 corresponds to oxidation of low-formal potential antioxidants and is an indicator of a sample’ s antioxidant potential. Q600 was deduced from cyclic voltammograms recorded for 1:50 dilutions of teas. The parameter Q600 once again resulted in separation of the three most potent teas and correlated well with the overall TP content as well as the content of powerful antioxidants, gallic acid and chlorogenic acid. This study confirms the usefulness and complementarity of rapid electrochemical techniques in elucidation of the antioxidant potential of food products. |
