Antioxidant activity and phenolic composition in 'Beauregard' sweetpotato are affected by root size and leaf age

Phenolic acids are considered important antioxidants that may help to prevent many human chronic diseases. The antioxidant activity and phenolic content of sweetpotato [Ipomoea batatas (L.) Lam.] roots and leaves of different sizes and ages, respectively, were quantified. Small roots (approximate to 4 g root weight) had a higher antioxidant activity and phenolic content compared with full-sized marketable roots (approximate to 300 g root weight). Phenolic content in marketable roots was significantly higher in the cortex tissue than in the internal pith tissue. The highest total phenolic content [chlorogenic acid equivalents (10.3 mg.g(-1) dry weight)] and antioxidant activity [Trolox equivalents (9.7 mg.g(-1) dry weight)] was found in cortex tissue of small-sized roots. Sweetpotato leaves had a significantly higher phenolic content and antioxidant activity than roots. Young, immature unfolded leaves had the highest total phenolic content (88.5 mg.g(-1) dry weight) and antioxidant activity (99.6 mg.g(-1) dry weight). Chlorogenic acid was the major phenolic acid in root and leaf tissues with the exception of young immature leaves in which the predominant phenolic acid was 3,5-dicaffeoylquinic acid. The results suggest that small-sized roots, which are typically discarded in the field, and young immature leaves may be concentrated sources of phenolic antioxidants.