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Flavonols, phenolic acids and antioxidant activity of some red fruits

Red fruits (blueberry, blackberry, chokeberry, strawberry, red raspberry, sweet cherry, sour cherry, elderberry, black currant and red currant) were analyzed for flavonols (quercetin, myricetin, and kaempferol), hydroxycinnamic acids (caffeic, ferulic, p-coumaric acid) and hydroxybenzoic acids (p-hydroxybenzoic, ellagic acid) by using HPLC method. Compounds were analyzed as aglycons after acid hydrolysis with 1.2 mol dm-3 HCl. Each fruit sample was analyzed for total polyphenols (TP) and total anthocyanins (TA). TP ranged from 1763 to 7194 mg kg-1 fresh weight (FW) in red raspberries and chokeberries, respectively. TA ranged from 169 to 4069 mg kg-1 FW in strawberries and blueberries, respectively. Flavonols varied from 4 mg kg-1 in red raspberries to 183 mg kg-1 in blueberries. Hydroxycinnamic acids were found in relatively high concentrations in blueberries (92 mg kg-1) and in black currant (70 mg kg-1) and represented significant portion in sour and sweet cherry phenolics. The amount of ellagic acid was high in blackberry (121 mg kg-1), strawberry (41 mg kg-1) and red raspberry (32 mg kg-1). The strongest antioxidant activity determined by DPPH• and ABTS• + assays showed chokeberry, followed by blueberry, black currant and elderberry. Antioxidant activity correlated better with TP than with TA, total flavonols (TF), or total hydroxycinnamic acids. Additionally, linear relationship was observed between antioxidant activity of fruits and content of caffeic acid, quercetin and p-coumaric acid. Overall results showed that red fruits can serve as good source of bioactive polyphenols in human diet, but due to high concentrations of anthocyanins, flavonols, phenolic acids and strong antioxidant activity, chokeberry, blueberry, elderberry and black currant can be regarded as good candidates for nutritional supplement formulations.

red fruits; berries; flavonols; phenolic acids; antioxidant activity

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