Determination of phenolic content, antioxidant activity, and brine shrimp toxicity of the aerial part extracts from Sinapis alba and Sinapis arvensis (Brassicaceae) growing wild in Sicily (Italy).

Abstract

As part of a project aimed at the valorization of taxa included in the Brassicaceae family belonging to the spontaneous flora of Sicily, our research team has recently focused on studying the taxa of Sinapis L., utilized as food plants and in traditional medicine as sources of bioactive compounds with application in pharmaceutical, nutraceutical and cosmetic fields. In Italy, the genus is represented by Sinapis arvensis L., S. pubescens L., and S. alba L., the latter consisting of three infra-specific subdivisions namely subsp. alba, subsp. dissecta (Lag.) Bonnier, subsp. mairei (H.Lindb.) Maire. All these specific and intraspecific taxa are present in Sicily. Particularly, current research is focused on the aerial parts (leaves, flowers, and stems) of Sinapis alba (white mustard) and Sinapis arvensis (wild mustard). The total phenolic and flavonoid content of the 70% methanol extracts from the aerial parts of the selected species has been spectrophotometrically quantified. Moreover, the antioxidant properties were determined by in vitro methods based on different mechanisms: the primary antioxidant activity was evaluated by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and reducing power assays, while the ferrous ion chelating activity assay estimated the secondary antioxidant properties. Finally, Artemia salina lethality bioassay was performed for the preliminary toxicity assessment. The total phenolic content was found to be higher in S. alba leaf, flower, and stem extracts (68.53 ± 2.57, 69.33 ± 1.83 and 47.01 ± 1.56 mg GAE/g extract, respectively) than those of S. arvensis. The same trend was also observed for the flavonoid content (32.94 ± 0.91, 29.93 ± 0.67 and 17.36 ± 0.41 mg QE/g extract, respectively). Concerning the antioxidant properties, all the extracts of the two species showed mild to moderate DPPH radical scavenging activity compared to the standard butylated hydroxytoluene (BHT); among the extracts, S. alba flower extract displayed the best activity, reaching 95% inhibition at the highest concentration tested (IC50 reducing power assay, both species showed mild to moderate reducing power, compared to the standard BHT being S. alba extracts more active than those from S. arvensis. In the ferrous ion chelating activity assay, S. arvensis extracts displayed good secondary antioxidant properties, higher than those from S. alba, with flower extract being the most active (IC50 = 0.15 ± 0.09 mg/mL) followed by stem and leaf extracts (IC50 = 0.22 ± 0.005 and 0.37 ± 0.08 mg/mL, respectively). The results of the antioxidant tests indicate that the extracts of the two Sinapis taxa possess antioxidant properties based on different mechanisms: the best primary antioxidant activity was observed for S. alba extracts, whereas those from S. arvensis displayed better secondary antioxidant properties. At last, the results of A. salina lethality bioassay showed the absence of toxicity against brine shrimp larvae for all the extracts. Overall, the obtained results improve the knowledge of the Sinapis taxa, also indicating S. alba and S. arvensis, belonging to the spontaneous flora of Sicily, as safe sources of antioxidant compounds.