Antioxidant activity and effective compounds of immature calamondin peel

► Water extract of immature calamondin peel (ICW) had the best antioxidant activity. ► The flavonoids in immature calamondin peel were higher than that in mature peel. ► The contents of polymethoxyflavones increased in calamondin peel during ripening. ► Naringin and hesperidin were the major antioxidants in ICW. ► 3′,5′-Di-C-β-glucopyranosylphloretin contributed to antioxidant activity in ICW.