Antifungal secondary metabolites from monanthotaxis littoralis with activity against mycotoxigenic fungi from maize

Abstract

This study involved isolation of compounds from the plant Monanthotaxis littoralis, screening and evaluating the activity of the compounds against mycotoxigenic fungi The non volatile secondary metabolites were extracted from the plant using methanol. The methanol extract was suspended in water and extracted with ethyl acetate. Hydro-distillation was used in the extraction of essential oils. Column chromatography and Preparative Thin Layer Chromatography (PTLC) was used in purification of compounds. The solvent system used for separation in this study was 9:1 chloroform ethyl acetate mixture. The isolated compounds were tested for their anti-mould activity against 31 most common and damaging mycotoxigenic moulds from three genera of fungi (Aspergillus, Fusarium and Penicillium) using paper disc diffusion inhibition method. The structural elucidation of the bioactive compounds was carried out by a combination of spectroscopic techniques that include 1 and 2 D high field NMR spectroscopy GC-MS spectroscopy and Mass spectrometry. The oil had eight major compounds which include (-)-Beta-necrodol, (+,-)-tetramisole among others while from the crude extract flavonoids 3, 5-dihydroxy-7-methoxy anthocynidines and 3, 7, 5’- trihydroxy anthocynidines were isolated and compound M whose structure could not be elucidated because of the limitation of the purification methods used was also isolated. The highest activity of the oil was against Penicillium purporogenum, Penicillium islandicum and Aspergillus niger with MIC of 26 mg/ml. These species had inhibition zones of 39.17 mm, 29.60 mm and 15.67 mm respectively. The extent of inhibition of fungal growth was dependent on the concentration of the secondary metabolites. The oil MIC generally ranged from 26 mg/ml and 103 mg/ml. The flavonoids mixture had the highest activity against Aspergillus ochraceus where MIC of 1 mg/ml. In general the non volatile compounds had MIC values ranging from 1 to 4 mg/ml against the mycotoxigenic fungi. These results show that the secondary metabolites isolated from Monathotaxis littoralis have antifungal activities against mycotoxigenic fungi found in foods. Thus these compounds are potential antifungal that can be used in food preservation systems to inhibit the growth of moulds and retard subsequent mycotoxins production.