The Total Phenolic Content, Total Flavonoids and the Antioxidant Capacity in Two Wild Species of Raspberry, Rubus persicus and R. caesius, at Different Maturity Stages of Fruits

Abstract   Background and Objectives Antioxidants can harness the oxidative stress caused by free radicals by releasing single electrons and hydrogen ions. Myriad plants including vegetables and fruits express enzymatic and non-enzymatic antioxidant properties which are used by humans to maintain health.. In this study we aim to compare the level of antioxidants and the amount of total phenolic and flavonoid compounds at three different stages of fruit ripening including immature, semi-ripen and fully matured fruits in two species of raspberry after a period of storage at freezer.   Materials and Methods Fruits of Rubus persicus and R. caesius were collected at different maturity stages including immature, semi-ripen and fully matured stages from natural habitats. The extracts of fruits were stored at -20 °C for 6 months. The antioxidant activities of extracts were determined using DPPH free radical purification and ferric iron regeneration ability (FRAP) methods in June, 2013 in Research Laboratory of Science and Technology Park of East Azerbaijan province. The content of phenolic and flavonoid compounds was also quantified according to Folin–Ciocalteu’s phenol and aluminum chloride methods, respectively. The antioxidant activity and total phenolic and flavonoid contents were compared between species at three maturity stages in a completely randomized factorial design with three replicates.   Results Both methods applied to examine the antioxidant activity revealed a high mean value in extracts from fully matured fruits compared with immature and semi-ripen fruits. The magnitude of antioxidant activity was significantly higher in R. caesius than R. persicus except that the amount measured by DPPH free radical purification level was similar between species at only fully matured stage. A significant difference was observed in both total phenolic and flavonoid contents between immature, semi-ripen and fully matured stages in both species (P < 0.05) except that the total flavonoid content was similar between semi-ripen and fully matured fruits in R. caesius.   Discussion Results showed that the highest antioxidant capacity was found in the fully matured stage of fruits in both species and thus the fully matured fruits might be capable of counteracting and even neutralizing free radicals. The results also showed that different species had different level of antioxidant activity. The level of total phenolic and flavonoid content at fully matured fruits was also higher than immature fruits in both species. Our results suggest that the antioxidant potential of raspberry can have several medicinal applications and play an important role by reducing the oxidative stress.