In vitro antioxidant activity and total phenolic content of the inflorescences, leaves and fruits of Sorbus torminalis (L.) Crantz.

The antioxidant potential of 70% methanolic extracts from the inflorescences, leaves and fruits of Sorbus torminalis (L.) Crantz was evaluated using three in vitro test systems: the DPPH (2,2-diphenyl-1-picryl-hydrazyl) and the ABTS [2,2-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid)] free radical scavenging assays, and the AAPH [2,2'-azobis-(2-amidinopropane) dihydrochloride]-induced [corrected] linoleic acid (LA) peroxidation test. The results were compared with the activity of the extracts obtained from the model antioxidant Sorbus species (Sorbus aucuparia L.), and also with the activity of phenolic standards such as quercetin, Trolox [(+/-)-6-hydroxy-2,2,7,8-tetramethylchroman-2-carboxylic acid], BHA (butylated hydroxyanisole), BHT (butylated hydroxytoluene) and TBHQ (tert-butylhydroquinone). The radical scavenging capacities of the S. torminalis extracts towards the DPPH radical were in the range of 62.0-244.1 micromolar Trolox equivalents/g d.w. of plant material. They were significantly (p < 0.05) correlated with the results of the ABTS test (r = 0.8535), and with the chain-breaking activities determined in the LA-peroxidation test (r = 0.9831). In comparison with the synthetic standards, the free radical scavenging capacity of the Sorbus extracts was remarkably higher than their chain-breaking activity. Both kinds of antioxidant effects of the extracts were significantly (R2 > 0.8097, p < 0.05) influenced by the total phenolic content (TPC) as determined by the Folin-Ciocalteu method. The plant tissues derived from S. torminalis exhibited lower antioxidant potentials than those of S. aucuparia by a factor of 1.5-3.2, partially due to the lower TPC levels (multiplicity factors of 1.2-1.9). After the original antioxidant capacities of the extracts were recalculated according to the TPC levels, the resulting antioxidant capacities of the phenolic fractions in the S. torminalis extracts were lower than those from S. aucuparia by a factor of 1.1-1.6, suggesting that the distinctive chemistry of the phenolic constituents also influences the antioxidant power of the two species.