Determination of polyphenols in white grape berries cv. Rebula

Branka Mozetič¹, Irma Tomažič¹, Andreja Škvarč², Polonca Trebše¹

¹Nova Gorica Polytechnic, Laboratory for Environmental Research, POB 301, 5001-SI Nova Gorica
²Agriculture and Forestry Institute Nova Gorica, Pri hrastu 18, 5000-SI Nova Gorica

Abstract
Rebula white grapes polyphenols are determined for the first time. We analyzed grapes sampled from 13 different vineyards in Goriška Brda. Total polyphenols were determined according to the Folin-Ciocalteu method. For the individual polyphenols determination we used high performance liquid chromatography (HPLC) - diode array detection (DAD) technique. The separation of polyphenols from grapes was performed using narrow bore C18 Luna column (Phenomenex, 2 x 150 mm, 3μm) and monitored at 320 nm. The majority of white grapes polyphenols was represented by four hydroxycinnamic acids (HCAs). According to their UV-Vis spectra and chromatographic retention properties they corresponded to trans-caftaric, trans-coutaric, cis-coutaric and trans-fertaric acid. To confirm the identity of separated polyphenols, they were also directed to the ion trap mass spectrophotometer (Finnigan LCQ Deca) fitted with electrospray ionization (ESI) probe. Spectra were recorded in negative mode between m/z 100 and m/z 500. The mass spectrometer was programmed to do two consecutive scans: a full mass (MS) and an MS² scan of the most abundant ion in the full mass spectra. The results confirmed the assumptive identification of three HCAs; trans-caftaric, trans-coutaric and trans-fertaric acids in white grape berries cv. Rebula based on HPLC-DAD analysis.

Key words: White grapes, HPLC-DAD, MS/MS, hydroxycinnamic acids