Adijat Funke Ogundola, Callistus Bvenura and Anthony Jide Afolayan
Department of Botany, University of Fort Hare, Alice, Eastern Cape, South Africa
Objective: To investigate the effect of different soil textures on chemical compositions and antioxidant properties of Solanum nigrum shoot essential oil extracts.
Methods: Four soils of differing texture were formulated from soil collected from a fallow land and Solanum nigrum, a nutraceutical wild vegetable was cultivated on them in the glasshouse. Essential oils were extracted from harvested fresh shoots by Solvent Free Microwave Extraction (SFME) using the Milestone Dry DIST (2004) apparatus. The oils were qualitatively and quantitatively analyzed with Gas Chromatography-Mass Spectrometry (GC-MS). Antioxidant properties were assayed using the DPPH and ABTS and the results were subjected to statistical analysis. Results: The GC-MS profiling revealed variations in the quality index (QI) and number of chemical constituents from S. nigrum oil. Geraniol and citronellol were two principal components of high quality common to all treatments although other compounds such as caryophyllene oxide, geranyl tiglate and geranyl formate were also present. Antioxidant properties of the oil extracts using DPPH and ABTS assays showed variations in their results. Statistical analysis showed that S. nigrum cultivated on clay loam soil had the highest antioxidant power in both assays. The IC50 values ranged from 1.196 to 1.594 μg /ml and 0.067 to 3.59 μg /ml in DPPH and ABTS assays respectively.
Conclusions: The present work indicates that soil texture has an effect on the quality, quantity and chemical compounds synthesised in S. nigrum shoots. Essential oil extracts have good antioxidant properties. The presence of citronellol and geraniol among the major compounds is a good indicator and confirmation of the plant’s role in physiological defensive mechanisms hence its use in the production of herbicides. In addition, the current study indicates that antioxidants respond well to S. nigrum cultivated on clay loam soils, hence cultivation as well as further studies on these soils are encouraged.
Keywords: Soil types, essential oils, cultivated, Solanum nigrum, chemical compounds, antioxidant properties.