Chemical, Nutritional and Some Biological Studies of theTubers Extracts of Plectranthus edulis

Abstract

Plectranthus edulis is a tuberous crop found in some parts of Ethiopia. Though this plant iscommon, the nutritional and medicinal potential has not been systematically investigated. Inview of this, the tubers were successively extracted with hexane, EtOAc and MeOH to furnish0.3, 0.7 and 2.5% yield, respectively. The yellowish oil hexane extract was analyzed by GC-MSafter conversion to fatty acid methyl esters using BF3-MeOH. Results revealed the presence ofpalmitic, stearic, oleic and linoleic acid with the latter accounts for 42%. The hexane and EtOAcextracts after silica gel column chromatography afforded three compounds namely methyllinoleate, α-spinasterol and 3,5,7-trihydroxy-6,4’-dimethoxyflavone. The study also demonstratesthat the EtOAc (76%) and MeOH (84%) extracts showed strong antioxidative activity in bothferric thiocyanate and DPPH assay. This is likely attributed to the presence of 3,5,7-trihydroxy-6,4’-dimethoxyflavone which scavenge the DPPH radical by 88%. The extracts were alsoexamined for their antibacterial activity against S. aurous, E. coli, P. mirabilis and K.pneumonia using disc diffusion method. The EtOAc extract displayed modest activity (inhibitionzone of 11 mm at 100 mg/mL) compared with ciprofloxacin used as standard drug. Theproximate compositions were determined and had ash, crude fat, crude fiber, moisture, proteinand carbohydrate contents ranged from 1.5 to 1.8%, 1.1 to 1.8%, 4.46 to 5.99%, 69.00 to75.00%, 6.65 to 10.24% and 6.17 to 11.99%, respectively. The protein, crude fat, carbohydrateand fiber contents of the tuber of P. edulis were superior to those values reported for sweetpotato. The mineral composition including Cd, Cr, Cu, Ni, Pb and Zn were analyzed using AASwhile the Ca, K and Na contents were determined using flame photometer. The level of Cr, Cu,Ni, Pb, Zn, Ca, K and Na were found to be in the range of 0.008-0.030, 0.100-0.191, 0.330-1.065, 0.016-0.023, 0.135-0.357, 13.800-22.800, 325.00-502.50 and 12.80-13.50 mg/100g on thedry weight basis, respectively. Therefore, the tuber can contribute enormously to the supply ofboth macro and micronutrients in our diet. The ratio of Na/K in the tuber is less than 1indicating the usefulness of this plant as nutraceutical against hypertension. Therefore, thenutritional profile and biological activities recorded in the present study demonstrated theusefulness of this plant as natural food and medicine.