Evaluation of fixed oil from seeds of maesa lanceolata for phytochemical constituents, physicochemical characteristics and biological activity

Abstract

Plants produce fixed oils with some lipophilic secondary metabolites that possess diverse applications in food/feed, industry, medicine and agriculture. Maesa lanceolata is one of such plant in Ethiopia with its seeds known to bear fixed oils and used for greasing clay made pan while baking “Injera”. The present study reports the yield, physicochemical properties, phytochemical constituents of M. lanceolata seed oil. Report on biological activities (insecticidal & antimicrobial) and acidbase indicator potential of crude oil and major compounds isolated were also included. The oil was extracted by soaking the seeds in petroleum ether for five days and the isolated oil was subjected to physicochemical and phytochemical analysis employing standard test protocols available including AOAC. Pure compound isolation and characterization was carried employing chromatographic separation of crude oil, physical and spectral analysis of isolated compounds. Serial concentration range (0.3125 % to 5 %) of the crude oil and isolated compounds were evaluated for biological activates on three insect pests (Maize weevil, Sitophilus zeamais; Termite, Odontotermes formosus and Bed bug, Cimex lectularius employing no-choice assay) & culture of five pathogenic microorganisms (Bacillus cerus, Staphylococcus aureus, Escherichia coli, Aspargilus niger and Fusarium spp in vitro using disc diffusion test method). Positive and negative controls were included in each test. The acid-base indicator potential of crude oil and major fraction isolated was also evaluated using simple titration method using Phenolphthalein for comparison. The seed has 30.4% oil yield. Physicochemical tests performed gave acid value (0.8±0.15), peroxide value (0.375±0.1) and saponification value (106.59±0.57). Preliminary Phytochemical tests performed on the oil indicate presence of terpenoids, quinines and alkaloids. Insecticidal activities carried using the crude oil and the major fraction isolated (MLO-4) confirm both to possess concentration dependent activities on all pests tested. 100% mortality was recorded for 5.00 % test samples (M. lanceolata oil /MLO-4) at 9/ 6; 3½/ 3½ and 3/- hrs against Maize weevil, worker termite and bed bug respectively. The antimicrobial tests carried confirm the crude oil and its fractions to have effect on all tested microorganisms except Escherichia coli and Aspargillus niger and the crude oil had better activity than its fractions. The Inhibition zones recorded (in mm) for susceptible organisms for the crude oil and its major fraction (MLO-3, (MLO-4) respectively were 9 mm, 12 mm 14 mm and (for Bacillus cerus), crude oil and MLO-2 14 mm & 10 mm, (for Staphylococcus aureus) and 11, 9, 11and8 (MLO, MLO-2, MLO-3 andMLO-4) respectively. The crude oil and its major fraction (MLO-4) both have shown sharp end point color change (from yellow to purple) almost similar to endpoint for Phenolphthalein. Column chromatographic separation of the crude oil led to isolation of MLO-2 (Rf 0.66). Based on spectral data ( 1 HNMR, 13 C and DEPT) and melting point data of MLO-2 we propose this compound to be an isomeric mixture of monohydrated alkylbenzoquinone (2-Acetoxy-5-hydroxy-6-methyl-3-tridecyl-1, 4- benzoquinone and 5-Acetoxy-2-hydroxy-6-methyl-3-tridecyl-1,4-benoquinone).