Chemical composition, antioxidant and anti-diabetic activities of Scorzonera Phaeopappa Boiss

Abstract

Wild edible plants have attracted an increasing interest from researchers as they represent important inexpensive sources of nutrients, minerals, antioxidants and vitamins, as well as natural treatments for diseases. The genus Scorzonera includes about 170 species distributed worldwide, many species of this genus are either consumed as raw vegetables or cooked. In addition to their edible properties, some of the species ha ve been used in traditional medicine for various purposes. Nine species of the genus Scorzonera are found in Lebanon, with one of the nine species, Scorzonera Pheopappa Boiss, found in Lebanon and used (its leaves) in in the Lebanese cuisine. Oxidative stress has been implicated in various pathological conditions including diabetes. The presence or intake of antioxidants protect the human body from oxidative stress. The aim of this study is to determine the total phenol, total terpene and total flavonoid contents, and antioxidant and anti-diabetic activities of Scorzonera Phaeopappa Boiss. Using dichloromethane, dichloromethane (pretreated with NH4OH), methanol acetone and ethanol, extracts were prepared from the edible leaves of the plant. The extracts were assessed for their total phenolic content using Folin-Ciocalteu method, total terpene content using Salkwoski test and total flavonoids content using aluminum chloride method. The antioxidant activity and the anti-diabetic activity were determined by 2, 2-diphenyl-1-picrylhydrazyl (DPPH) scavenging/ Fe2+-chelating assays and alpha-amylase/ alpha-glucosidase inhibitory assays, respectively, acarbose, a pharmaceutical drug used for treatment of diabetes, was used as standard reference. Dichloromethane (pretreated with NH4OH) was found to have the highest extraction capacity on phenols (2.73 mg Gallic acid equivalent /100 mg leave extract) and terpenes (232.42 mg linalool equivalent/100mg leave extract)methanol was found to have the highest extraction capacity on total flavonoids (63.05 mg Quercetin equivalent/100mg leave extract). In addition, the methanol extract exhibited the highest DPPH scavenging activity (IC50 0.07 mg/mL) and the highest chelating activity compared to other extracts (0.08mg/ml, chelating activity 50%). Acetone extract (0.21mg/ml) was two times more active than acarbose (0.47mg/ml) against alpha amylase enzyme and was the most active against alpha glucosidase (6.3mg/ml). Significant positive strong correlations were observed between total phenol content and alpha glucosidase inhibitory assay (r: 0.900 p: 0.037) and total terpene content and alpha glucosidase inhibitory assay (r: 1.000 p>0.0001). Further investigation for the anti- diabetic activity should be performed in order to identify and isolate the bioactive metabolites responsible for the activity.