Determination of fungi and mycotoxins in South African wheat and wheat-based products

M.Tech.Mycotoxins are toxic substances naturally produced by moulds (fungi) that may contaminate agricultural commodities by growing on grain or feed. These moulds produce in a variety of dangerous mycotoxins, such as aflatoxin, fumonisin, deoxynivalenol (DON), ochratoxin, and zearalenone, and may induce acute or chronic effects (carcinogenic, mutagenic, tetragenic and oestrogenic) in humans and animals if ingested. Wheat is an important cereal grown in most provinces of South Africa and yet little is known with respect to incidence of its infection with fungi, contamination with mycotoxins or what carry over of these toxins is into human food. The purpose of this project is to investigate the incidence of fungi and mycotoxins in samples of wheat taken from specified areas in South Africa with a view to finding out if there is indeed a problem and, if so, what would be its impact on the industry and consumers. This pilot project would then form the basis for further studies in other geographical areas and how wheat-based foods for human consumption are affected. Mycotoxins have probably been present in food and feed since the beginning of human existence. Some of their effects have been known for hundreds of years. The technology to detect and chemically characterize them has only really developed in the last 40 years, particularly since 1980. Very small quantities of many of the important mycotoxins can now be detected and accurately measured in foods and feeds. In addition to those already known, many others are known to exist, but have not yet been chemically characterized. Scientists are now identifying toxic compounds in food faster than the information can be processed. However, to maintain perspective, it must be remembered that these substances have always been there, that humans have always been eating the food in which they occur and in the case of many substances, only the dose makes the poison. This study investigated the presence of toxigenic fungi and mycotoxins in wheat and wheat-based products, and also did a pilot study on a few heavily contaminated field wheat (HCFW) samples. Fusarium species dominated the mycological contamination at 40 to 65%, Aspergillus 45%, Penicillium 41% Mucor and Rhizopus were also detected. Among the Fusarium species isolated, six were identified as F graminearum, F. solani and F. vertillioides-like and F subglutinans. Phoma species were also isolated. Quantitative and qualitative analysis by, multi-mycotoxin screen method and VICAM method to analyze foods and feeds was used. Deoxynivalenol was the most prevalent at 45% incidence in samples with a mean concentration of 4.6ppm, aflatoxins in 12% of the samples with a mean concentration of 1.2ppb, ochratoxin in 16% of the samples with a mean of 1.5ppb, zearalenone in 18% of the samples with a mean of 0.1ppb. Attention was drawn to the potential presence of fumonisin in wheat, where fumonitest VICAM method was used, fumonisins were detected on few samples at very low levels of 1 to 2ppm in commercial wheat, and a high reading of 49ppm was recorded on one of the heavily contaminated field wheat (HCFW) samples. Confirmation of these results was carried out with the use of the liquid chromatography coupled with mass spectrum (LC/MS) and high-pressure liquid chromatography (HPLC) system. These results indicate an incidence of mycotoxin in these products, a recommendation of monitoring for prevention of moulds and mycotoxins is suggested. Since health concerns related to dietary exposure to mycotoxins depend on the levels of mycotoxins in the food as consumed, on the amount of food consumed and on the body weight and physiology state of the individual. Therefore, there is a likely possibility that in South Africa, some of the population is exposed to mycotoxins through consumption of wheat and its by-products