Investigation of pure grape juices on their content of resveratrols

Content of resveratrol-derivates was analyzed in commercial grape juices. T he obtained results were compared with experimental juices of pure varietie s. In white commercial samples only little amounts of resveratrol-derivates could be found (mean: 0.5 mg/l; max. 2.2 mg/l; min. < 0.1 mg/l), in red ju ices significantly more (mean: 3.1 mg/l, max. 12.5 mg/l, min. < 0.1 mg/l). In white variety pure juices the amounts were also low (mean: 0.2 mg/l, max . 0.5 mg/l, min. < 0.1 mg/l), in red juices again quite high (mean: 6.3 mg/ l, max. 15.3 mg/l, min. < 0.1 mg/l). In variety pure juices the resveratrol -content depended on the variety as reported for wine. Blending of red with white juice could not he proved by resveratrol-content, but possibly by th e percentile content on polyphenols, because e.g. commercial samples contai n rather small concentrations of anthocyanins (13% of whole polyphenol cont ent, in variety pure juices more than 60%). The antioxidative capacity is q uite higher in the variety pure juices (mean: 16.1 mmol/l, max. 36.2 mmol/l ) than in the commercial ones (mean: 5.0 mmol/l, max. 12.9 mmol/l). These p arameters, in combination with the polyphenol content (estimated by Folin-m ethod), could eventually been used to prove a blending of red grape juice w ith white ones.