In vitro antioxidant activities and phenolic content in crop residues of Tunisian globe artichoke

The phenolic content and in vitro antioxidant activity of the bracts, leaves and floral stems of two Tunisian globe artichoke cultivars ('Violet d'Hyéres' and 'Blanc d'Oran') were assessed; the tests used to assay antioxidant activity were based on ABTS [2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid] and DPPH [2,2-diphenyl-l-picrylhydrazyl]. In addition reducing power was measured and the phosphomolybdenum total antioxidant activity assay was included. The bracts of 'Violet d'Hyéres' possessed, on average, twice the quantity of phenolic compounds than those of 'Blanc d'Oran'. They also had a higher content of 3,5-O-dicaffeoylquinic acid. The bracts and floral stems contained high levels of total caffeoylquinic acid, whereas the leaves provided a potentially exploitable source of luteolin. Ethanolic extracts of both cultivars exhibited a high level of antioxidant activity. The ABTS EC50 value was high in extracts from the leaves of both cultivars, whereas the DPPH test showed no variation between the bracts, floral stems and leaves. The bracts were associated with strong reducing power and total antioxidant activity. Overall, the leaves were associated with more antioxidant activity than the bracts or the floral stems. The implication is that globe artichoke crop residues could provide a useful source of antioxidant compounds.