4.3. Sample Preparation and Analysis of the Study Beverages
The study beverages (PRB and placebo drink) were produced at the Hochschule Geisenheim (Germany) and filled into in brown 750 mL bottles. The concentrates, juices and other materials were provided by Eckes-Granini Group GmbH (Niederolm, Germany), riha WeserGold GmbH & Co. KG (Rinteln, Germany), and ADM Wild Europe GmbH & Co. KG (Eppelheim, Germany). The PRB with 73% juice content was produced from water, rectified grape juice from concentrate (22%), chokeberry juice from concentrate (17%), cranberry juice from concentrate (17%), and pomegranate juice from concentrate (17%). The placebo drink was prepared from water, rectified grape juice from concentrate, citric and malic acids, and flavorings.Soluble solids (Brix values) were measured refractometrically in accordance with the International Fruit and Vegetable Juice Association (IFU)-8 method (2017). For determination of myo-inositol as well as sorbitol ion chromatography with electrochemical detection was used, which was based on the IFU-79 method (2011). The sugar content of glucose and fructose was determined enzymatically with the method ASU L 31.00-12 (1997-01), citric acid with ASU L 31.00-14 (1997-01), and malic acid with ASU L 31.00-15 (1997-01).Total polyphenol content was determined using the Folin-Ciocalteu-Assay and expressed as the concentration of GAE as previously reported [The antioxidative capacity was determined using the TEAC assay according to method published by Re et al. [Identification of the anthocyanins and copigments by HPLC-ESI-MS/MS as well as quantification by ultra-high-performance liquid chromatography-diode array detector (UHPLC-DAD) was performed as described before by Niesen et al. [