Composition and antioxidant activity of grape seed extract (GSE) obtained from red
grape varietes are very well documented, in contrast to the white varietes. This paper
presents the results of polyphenols content of ethyl acetate extract of grape seeds, obtained
from two white grape varieties, Italian Riesling and Župljanka, and their antioxidant
activity on the stable DPPH radical. The influence of the addition of GSE to raspberry
juice on the DPPH radical was also examined. Content of total polyphenols in GSEs
ranged between 81.6 and 82.8% (w/w), and the contetn of flavan-3-ols between 66.2 and
91.0% (w/w). HPLC results showed that the most abundant components in the extract
were (+)-catechin and (-)-epicatechin for both grape varieties. All tested GSEs exhibited
good antioxidant activity. IC50 values for the GSEs of Italian Riesling and Župljanka
were 0.79 and 0.95 mg sample/mg DPPH radical, respectivelly. Since the GSE of Italian
Riesling possesed stronger antioxidant activity, it was used for further experiments. The
IC50 value for raspberry juice was 4.18 mg raspberry juice/mg DPPH. The raspberry
juice with addition of 0.60 μg/mL of GSE showed antioxidant activity of 39.2%. The same
juice with the threefold concentration of vitamin C (1.81 μg/ml) exhibited similar antioxidant
activity (33.9%). Antioxidant activity of the same amount of juice without added antioxidants
was lower (15.7%). The results showed that the GSE of white varietes could be
considered as a good functional food ingredien