Phenolic compounds and antioxidant activity of twelve grape cultivars measured by chemical and electrochemical methods

Five red (Rondo, Cabernet carol, Merlot, Pinot noir, Cabernet sauvignon), five white (Solaris, Riesling, Johanniter, Aurora, Saphira), and two pink (Freiminer, Gewurztraminer) grape cultivars were investigated. The phenolic content was determined by liquid chromatography–mass spectrometry quadrupole time-of-flight (LC-MS QTof) and ultra-performance liquid chromatography-photodiode array-fluorescence (UPLC-PDA-FL); and the antioxidant activity by two spectrophotometric methods: oxygen radical absorbance capacity (ORAC) and 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS° + ), and by cyclic voltammetry (CV). The aim of this study was to determine profile of phenolic compounds of popular cool climate grape cultivars and their antioxidant potential. The used methods were compared and correlations were established between investigated parameters. Total phenolic content ranged from 1354.6 mg/100 g in dry weight (d.w). for Aurora to 4567.9 mg/100 g d.w. for Rondo. Highest antioxidant activity was observed in red cultivars Rondo, Merlot and Pinot noir (24.4, 23.6 and 21.3 mmolTrolox/100 g d.w., ABTS° + assay), while in pink and white cultivars results not exceeded 20 mmolTrolox/100 g d.w. The aforementioned affect in red grapes was associated with their higher content of phenolic compounds, and the presence of an additional group, i.e. anthocyanins. Cyclic voltammetry measurements of redox potential of phenolics confirmed the results achieved by traditional methods of evaluating antioxidant activity. Red cultivars had the highest anodic curve area.