Influence of the harvest stage on the phenolic composition and bioactive properties of Cynara cardunculus L. var. altilis heads
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Cynara cardunculus L., commonly known as cardoon, is an erect perennial herbaceous plant. It belongs to the Asteraceae family and it is native to the Mediterranean area. This species comprises three taxa: the wild cardoon (var. sylvestris), the domesticated cardoon (var. altilis) and the globe or head artichoke (var. scolymus) [1]. Their edible capitula are widely used in several food recipes and as an herbal medicine, due to their known health-promoting effects and richness in bioactive compounds. The diverse industrial applications attributed to this crop (e.g. cheese manufacturing, biomass production, bioenergy and solid biofuels production, and pharmaceutics) make its cultivation highly important and with economic impact [1-3].
Thus, due to its increasing consumption and commercial interest, the present study purposes the analysis of phenolic compounds and bioactive properties of cardoon heads at different harvest stages. Cardoon (var. altilis) head samples were collected in Greece, at five different harvesting times, presenting therefore different maturation stages. The phenolic composition was determined in hydroethanolic extracts by HPLC-DAD-ESI/MS. The antimicrobial activity was tested against three Gram-positive and three Gram-negative bacteria, and six fungi species using the microdilution method. The cytotoxic effects were evaluated against four human tumor cell lines and in a porcine liver primary cell culture using the sulforhodamine B assay. The anti-inflammatory activity was evaluated through the inhibition of NO production using lipopolysaccharide-stimulated macrophages. Finally, the antioxidant activity was measured by TBARS and OxHLIA assays.
Nine phenolic compounds were tentatively identified, with cis 3,4-O-caffeoylquinic acid and apigenin-O-glucuronide being present in higher quantities. The content of phenolic compounds decreased with maturation process; the latest harvest caused a loss of 78% of the phenolic content. All the tested samples exhibited antibacterial and antifungal activity; but unlike the findings for phenolic content, the mature heads revealed the lowest MICs. Regarding the cytotoxic activity, the earliest harvest (immature heads) revealed activity against all the tumor cell lines tested, except for breast cancer cell lines for where the latest harvest had the highest potential. Moreover, the mature head extracts presented capacity to protect erythrocytes from the free radicals generated in the reaction system. Regarding the anti-inflammatory activities and TBARS inhibition, the immature heads revealed the highest activity. The heterogeneity of the biological results reveals that other compounds than phenolic ones may be correlated with these bioactivities.
This study proved the high biological potential of cardoon heads as also its possible use as a source of important bioactive compounds. Nevertheless, further studies are needed to understand which compounds are responsible for the observed bioactivities, as well as to find the stage of maturity that provides the best bioactive properties.
