A survey of South African commercial feed grade maize for mycotoxins with particular reference to fumonisins using different analytical techniques

• Main Author: Chilaka, Cynthia Adaku
• Published: 2012
• Subjects: Corn - Diseases and pests; Mycotoxins
• Online Access: http://hdl.handle.net/10210/8057

M.Tech. === Maize (Zea may) is the third most important cereal in the world serving various purpose of economic importance especially as staple diet to the Africans and as a major component of animal feed. Unfortunately, this commodity serves as a suitable substrate for pest and fungi development which may result in the production of mycotoxins. Mycotoxins are secondary metabolites of varying chemical structures produced by filamentous fungi, which may contaminate agricultural commodities either in the field or at storage. Mycotoxins have been implicated to cause several diseases in humans and animals ranging from acute to chronic. This study was designed to determine and quantify the occurrence and levels of mycotoxins in South African feed grade commercial maize. A total of 40 commercial feed grade maize samples were randomly sampled from two factory sites (Factory A and Factory B) of a commercial feed company source from known South African maize producers. The samples were screened for fungi using the conventional method while the mycotoxin screening and quantification was done by thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). In addition to TLC and HPLC, VICAM/HPLC, VICAM/fluorometer, enzyme linked immuno-sorbent assay (ELISA) and lateral flow method were used for determination and quantification of fumonisins. The mycological investigation revealed the occurrence of several fungal species of Fusarium, Aspergillus and Penicillium with Fusarium being the most prevalent (100%). Among the Fusarium spp. were F. verticillioides, F. proliferatum, F. oxysporum and F. graminearum, F. subglutinans, F. chlamydosporum, F. solani, F. poae and F. dimerum. Fusarium verticillioides and F. proliferatum had the highest incidence rate of 89% and 73%, respectively, followed by F. oxysporum (65%) and F. graminearum (48%). The rate of occurrence of A. fumigatus, A. flavus and Penicillium spp. were 45%, 43% and 38%, respectively. Further analysis on the isolated fungal strains proved that over 50% of the fungal spp. were toxigenic. Mycotoxicological study on the samples revealed that the samples were contaminated with fumonisins (FB), aflatoxins B (AFB), ochratoxin A (OTA) and zearalenone (ZEA) on TLC. Mycotoxins levels in the samples were confirmed on HPLC, with the levels ranging from 0.064-1.035 ppm for FB, 0-0.762 ppm for iii AFB, 0-0.194 ppm for OTA and 0-0.135 ppm for ZEA. There was no significance difference on mycotoxin concentration in the feed grade sample between the two factory sites. Results obtained from the VICAM methods, ELISA and lateral flow method for FB determination showed 100% incidence rate of the feed grade maize samples similar to that observed on HPLC. Although ELISA (0.190-2.450 ppm) and lateral flow method (0.350-2.700 ppm) showed higher concentration of FB compared to HPLC (0.064-1.035 ppm), recovery analysis on sample using lateral flow gave high value (85%) comparable to HPLC. Further analyses were performed to determine the cytotoxic potential of the feed grade maize samples using the fumonisin fraction (FFraction). The data obtained showed that the feed grade maize extracts were toxic on human peripheral blood mononuclear cells (HPBMC) and the degree of effect on the cells is dependent on the concentration of FB and the duration of exposure. However using oneway ANOVA to determine the effect of different concentration (volumes) of toxin and time of exposure on HPBMC in this study, it was observed that there was no significant difference regardless of the concentration and time.