Changes in polyphenol content during production of grape juice concentrate

Abstract

The production of grape juice concentrate on an industrial scale was evaluated and samples from the main steps of processing have been collected and analyzed. The sampling steps included the selection and washing of grapes (Nevsehir Patlak variety), pressing in order to obtain the juice separate from the seed and the skin fraction, pasteurization, clarification, filtration, evaporation, and filling-packing at 27°C with a Brix of 45°. Samples from each of the processing steps were analyzed by a number of spectrophotometric analyses. A series of anthocyanin compounds was identified using HPLC-MS, and the fate of anthocyanins, quercetin rutinoside and procyanidins was followed using HPLC. The results indicate that the removal of seed and fruit skin removes most of the procyanidins and anthocyanins, while subsequent clarification and filtration treatments further reduce the anthocyanin content.