Variety and ripening impact on phenolic composition and antioxidant activity of mandarin (Citrus reticulate Blanco) and bitter orange (Citrus aurantium L.) seeds extracts

Changes of antioxidants in the seeds of mandarin (Citrus reticulata) and bitter orange (Citrus aurantium) fruits during three stages of ripening (IM, SM and CM) were evaluated. Comparison between the two varieties showed that Mandarin exhibited the highest total polyphenols and flavonoids contents at IM and SM stages, respectively while bitter orange possesses the highest tannins content at SM stage. A total of 22 phenolic compounds were identified in mandarin and bitter orange seeds, including hydroxybenzoic acids (3), hydroxycinnamic acids (6), flavanones (3), flavanols (2), flavonols (3), flavones (3), simple phenol (1) and coumarin (1). The percentages of phenolic classes were found to vary during ripening which extents depended on the variety. During mandarin ripening, IM, SM and CM stages were characterized respectively by the presence of naringin, hesperidin and gallic acid as the most abundant mandarin compounds. In the case of bitter orange, naringin and neohesperidin were the major compounds during fruit maturation. Antioxidant activity was employed by two complementary test systems namely DPPH free radical scavenging and β-carotene/linoleic acid systems. The antioxidant capacity varied during ripening with bitter orange activity being higher than that of mandarin.

► Ripening stage influence phenolic content and antioxidant activity of citrus seeds.
► The highest polyphenols and flavonoids contents are found at maturity in mandarin seeds and at immature and semi matures stages in bitter orange.
► Mandarin seeds are rich on gallic acid at maturity.
► Bitter orange seeds are a source of naringin and neohesperidin during ripening.