Comparison of Phenolic Composition, Ripeness Parameters and Antioxidative Capacity of 33 Table Grape Cultivars

Table grapes are one of the most consumed fruits worldwide. It is assumed that consumption of table grapes has positive effects on blood composition and general health due to their content of phenolic substances. To obtain knowledge about the chemical composition of table grape varieties grown in Austria, the berries of 33 table grape cultivars of the genus Vitis vinifera L. were analysed over a 3-year period. The main focus was on phenolic composition (flavonoids, stilbenes, anthocyanins, phenolic acids), which was analysed using different high-performance liquid chromatography (HPLC) techniques. Ripeness parameters (sugar, acids, pH value) were determined using Fourier transform infrared spectroscopy (FTIR) analysis. The antioxidative capacity was measured using the 2,2 '-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) method. Most parameters were studied in skin and pulp. The sugar content ranged from 9.5 to 20.5 degrees KMW (95-205 g sugar/kg) and the content of titratable acid varied between 1.7 and 9.0 g/L. The lowest values for tartaric and malic acid were 1.6 and 0.3 g/L, and the highest values were 5.4 and 5.3 g/L, respectively. The pH varied between 3.2 and 4.2. The antioxidative capacity was in the range of 0.6-20.6 mmol/L Trolox. The flavonoid and phenolic acid content was in the milligram per litre range, with the highest values for caftaric acid in pulp (maximum: 76.4 mg/kg). In addition to considerable differences between cultivars, a multivariate data analysis showed a large deviation between the harvest years. Using cluster analysis with dendrograms, the chemical relations between cultivars were reported quantitatively. The present work reveals that for a description of table grape cultivars, it is necessary to consider the influence of vintage year, harvest date and overall ripeness. Furthermore, it is demonstrated that the composition of Austrian table grapes is in good accordance with data from the literature.