Denis Rusjan,* Zora Korošec-Koruza

University of Ljubljana, Biotechnical Faculty, Jamnikarjeva 101, SI-1001 Ljubljana, Slovenia.
Tel.: +386(0)14231161,
Fax: +386(0)14231088,
E-mail: denis.rusjan@bf.uni-lj.si.

Paper based on a presentation at the 12^th International Symposium on Separation Sciences, Lipica, Slovenia,
September 27–29, 2006.

Abstract
The content of phenolic compounds in grape skins of the red grape variety “Merlot” using different extraction solvents and analytical techniques were studied. The 1% solution of 2,6-di-tert-butyl-4-methylphenol (BHT) in methanol and ethanol/ formic acid/water solution were used as extraction media, and the content of phenolic compounds was determined using HPLC and spectrophotometry. Methanol compared to ethanol/formic acid/water performed better, as statistically significantly higher contents were determined.
The following contents were determined: (+)-catechin 68–74 mg kg^–1, (-)-epicatechin 32–35 mg kg^–1, oenin 440–450 mg kg^–1, rutin 2.9–3.5 mg kg^–1, myricetin 0.4–0.5 mg kg^–1, kaempferol 2.3 mg kg^–1 and quercetin 3.2–3.6 mg kg^–1. Using spectrophotometry, an arbitrary procedure was followed for determination of phenolic compounds extracted with ethanol/formic acid/water. Thus, the content of total phenols (791–1127 mg kg^–1), tartaric esters (219 mg kg^–1), flavonols (163–167 mg kg^–1) and total anthocyanins (2179–2219 mg kg^–1) was determined. A comparison with literature data is difficult due to different varieties studied, ecological conditions, ripening stage, analytical methods etc., but some similarities can be observed. For our understanding of the process of grape maturation and its quality, it is of importance to develop a reliable and simple method.

Keywords: grape analysis, wine, extraction, antioxidants, chromatography, spectrophotometry