Evaluation of fungal and mycotoxin contamination of maize consumed in the North West Province of South Africa

Abstract

The North West province of South Africa ranks the second major maize producing region in the country after the Free State, South Africa. In the North West province, as is the case in much of the world, fungal and subsequent mycotoxin contamination of maize is of great concern. This is because maize constitutes the major staple food, and is produced on a small scale and also commercially. It is also extensively used as livestock feed and also serves as an export crop. Losses incurred as a result of fungal growth and contamination of cereal grains are not only of trade and industrial importance, but are also of significant public health and animal health concern due to possible production of mycotoxins by these fungi. Mycotoxins are prevalently toxic compounds produced as secondary metabolites by various fungi and excreted on agricultural crops at pre and post-harvest stages of food and feed production under a wide range of climatic conditions. This present study was carried out to evaluate the incidence of fungal species and mycotoxins contaminating small -scale and commercial maize grains in the North West province of South Africa and to evaluate potential health risks for consumers based on South African and international regulations. A total of 100 maize samples were randomly collected from commercial and small-scale farmers across the North West province of South Africa. Samples were investigated for funga l contamination using conventional (macroscopic and microscopic) and molecular phylogenetic methods to identify fungal species. Mycotoxin analysis was also carried out using validated methods. The percentage incidence of different genera isolated revealed the predominance of Fusarium (82%), Penicillium, (63%) and Aspergillus species (33%) compared to other genera. Among the species, Fusarium verticilloides had the highest incidence of 70 and 76% in commercial and small-scale maize respectively, while P. digitatum had 56% total incidence and Aspergillus fumigatus (27%) were also the most dominant of these genera. The data obtained from HPLC, ELISA and TLC revealed that the maize samples were contaminated by FB, ZEA, OTA and AFB. Furthermore, the analysis of mycotoxins by HPLC revealed that FB1 was the most contaminant mycotoxin in the small-scale and commercial maize samples with the incident rate of I 00 and 98.6% respectively. Aflatoxins contamination in both samples occurred at incidences of 26.7% in small-scale samples and 25.0% in commercial samples. The levels of AFs varied between 0.080-9.34 μg/kg and 0.32-8.60 μg/kg in small scale and commercial samples

respectively. Furthermore, OTA had a high incident rate of 97.8% and 93.0% which ranged from 3.60-19.44 to 1.60-9.89 μg/kg respectively in small-scale and commercial maize samples while ZEA occurred in 50 and 55% of small-scale and commercial maize samples respectively with mean concentrations of 39.2 and 17.5 μg/kg respectively. In addition, sample contamination levels for ZEA ranged between 0.2-51 .3 to 0.1-36.8 μg/kg respectively and the values were below the acceptable limits of I 00 μg/kg for ZEA in maize intended for human consumption (EU, 2007). Furthermore, most of the maize samples analysed showed simultaneous occurrences of two or more mycotoxins. The low incidence of mycotoxins m the maize samples is in contrast to results from other provinces (Limpopo, KwaZulu Natal, Gauteng and Eastern Cape) of South Africa and other countries in Africa. The arid and semi-arid climatic conditions that characterised the sampled area might be responsible for this.The results also showed that maize from small-scale farmers may contribute to dietary exposure to mycotoxins. Farmers and consumers should be aware of the dangers of fungal and mycotoxin contamination of maize with resultant health risks. However, several researchers have analysed and quantified mycotoxins in different parts of the country, especially fumonisins but the novelty of this study is that to our knowledge there are limited reports from North West province so far on the occurrence of fungi and mycotoxins on food commodities.