Impact of processing and storage on the phenolic profiles and contents of pomegranate (Punica granatum L.) juices

Juices were obtained on pilot-plant scale from untreated, steamed and peeled pomegranate fruits (Punica granatum L.), respectively, by applying increasing pressures and various juice treatments, i.e., enzymatic treatment, filtration, clarification and pasteurization, to determine the influence of process technology on the phenolic profiles and contents of the juices. Polyphenols were characterized and quantified by HPLC-DAD-ESI/MSn, and total phenolics and antioxidant capacity of the juices were determined by Folin-Ciocalteu, FRAP and TEAC assays, respectively. The total amounts of anthocyanins and colorless phenolics in the juices significantly differed depending on the applied technology. Highest phenolic recoveries were obtained from steamed fruits without further treatment. In contrast, lowest phenolic contents were determined in the juices produced from peeled fruits, i.e., the isolated seeds with adherent arils. With increasing pressures, polyphenol recoveries were enhanced, whereas juice treatments such as microfiltration and fining lowered phenolic contents of the juices. Furthermore, the amounts of individual phenolics were determined by HPLC-DAD with ellagitannins dominating the phenolic profiles. Juices solely produced from the edible parts of pomegranate exhibited lower amounts of ellagitannins compared with the juices from entire fruits. In contrast, the former juices were characterized by the highest amounts of gallotannins, hydroxybenzoic acids, hydroxycinnamic acids and dihydroflavonols. These results were consistent with the astringency of the juices. Additionally, storage experiments were performed at 4 degrees C and 20 degrees C in the dark and 20 degrees C under light exposure, revealing significant pigment degradation and concomitant color loss, especially at elevated temperatures and upon illumination, whereas the contents of non-anthocyanin phenolics and antioxidant capacity remained virtually unchanged throughout storage.