Effect of processing and storage on the antioxidant ellagic acid derivatives and flavonoids of red raspberry (Rubus idaeus) jams

From red raspberries, ellagic acid, its 4-arabinoside, its 4 ' (4 " -acetyl ) arabinoside, and its 4 ' (4 " -acetyl)-xyloside, as well as quercetin and kaempferol 3-glucosides, were identified. In addition, two unidentified el lagic acid derivatives were detected. The free radical scavenging activity of the ellagic acid derivatives was evaluated by using the DPPH method and compared to that of Trolox. All of the isolated compounds showed antioxidan t activity. The effect of processing to obtain jams on raspberry phenolics was evaluated. The flavonol content decreased slightly with processing and more markedly during storage of the jams. The ellagic acid derivatives, wit h the exception of ellagic acid itself, remained quite stable with processi ng and during 6 months of jam storage. The content of free ellagic acid inc reased 3-fold during the storage period. The initial content (10 mg/kg of f resh weight of raspberries) increased 2-fold with processing, and it contin ued increasing up to 35 mg/kg after 1 month of storage of the jam. Then a s light decrease was observed until 6 months of storage had elapsed. The incr ease observed in ellagic acid could be explained by a release of ellagic ac id from ellagitannins with the thermal treatment.