Doctor of Philosophy / Fumonisins B1 6 and B3 8 are toxic secondary metabolites of the fungus Fusarium moniliforme that inhibit enzymes of sphingolipid biosynthesis. This dissertation describes work towards the stereocontrolled total synthesis of the fumonisin natural products. The proposed highly convergent strategy allows for the late stage stereocontrolled coupling of the two fragments C1-C10 58 and C11-C20 57 with concomitant installation of the C10 hydroxyl using key boron aldol methodology. A directed hydrogenation installs the final methyl-bearing stereocentre at C12. Syntheses of the left- and right-hand fragments 57 and 58 by means of substrate-based stereocontrol and asymmetric catalytic methods is reported. A completed synthesis of the protected FB3 carbon backbone 59 is achieved in a linear reaction sequence of 14 steps. Tentative assignment of stereogenic centres within 59 was made by analogy to the C4-C20 fragment 190 of fumonisin B3. Synthesis of C4-C20 190 by the coupling of C11-C20 57 with heptaldehyde is also described.

Doctor of Philosophy / Fumonisins B1 6 and B3 8 are toxic secondary metabolites of the fungus Fusarium moniliforme that inhibit enzymes of sphingolipid biosynthesis. This dissertation describes work towards the stereocontrolled total synthesis of the fumonisin natural products. The proposed highly convergent strategy allows for the late stage stereocontrolled coupling of the two fragments C1-C10 58 and C11-C20 57 with concomitant installation of the C10 hydroxyl using key boron aldol methodology. A directed hydrogenation installs the final methyl-bearing stereocentre at C12. Syntheses of the left- and right-hand fragments 57 and 58 by means of substrate-based stereocontrol and asymmetric catalytic methods is reported. A completed synthesis of the protected FB3 carbon backbone 59 is achieved in a linear reaction sequence of 14 steps. Tentative assignment of stereogenic centres within 59 was made by analogy to the C4-C20 fragment 190 of fumonisin B3. Synthesis of C4-C20 190 by the coupling of C11-C20 57 with heptaldehyde is also described.

Thesis (Ph. D.)--University of Sydney, 2004. / Title from title screen (viewed April 6, 2009). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Chemistry, Faculty of Science. Degree awarded 2004; thesis submitted 2003. Also available in print form.

The mycotoxin zearalenone is known for its harmful effects on livestock reproduction. Animal exposure occurs through feed sources colonized by Fusarium species which produce the mycotoxin. Since regular screening procedures for zearalenone are not conducted on Western Canadian barley, a survey was carried out to test for possible significant levels of contamination. All samples were found to be negative at a detection level of 500 ppb; therefore, feeds formulated from the barley samples sources would not likely cause zearalenone toxicosis problems in livestock. Also, an ELISA method, Agri-Screen™, developed by Neogen Corporation (Lansing, Michigan) was tested and found to be a simple and economical method for pre-screening of feed samples in the field. To study direct toxicological effects of zearalenone on in vitro murine blastocyst development, murine embryos were cultured in medium (Ham's F-10 + estrous cow serum) containing various levels of the mycotoxin. The critical concentration range for zearalenone to cause detrimental effects on blastocyst development was determined to be between 70-160 μg/ml medium. Additionally, a concentration effect on the length of time required to exert deleterious actions was demonstrated. At mycotoxin concentrations of 500 μg/ml medium and above, blastocysts degenerated after 6 h of culture. At a lower concentration level of 160 μg/ml, blastocysts were not affected until 28 h of culture. In order to investigate the direct toxicological effects of zearalenone on in vitro porcine pre-implantation embryo development, attempts were made to develop a successful culture system. Since a suitable system was not developed, toxicological studies were not possible. Possibly, steps in the recovery process could have resulted in detrimental effects before the embryos were placed in culture. Alternatively, the media chosen (Ham's F-10 + estrous cow serum; Minimum essential medium + fetal calf serum) may not be suitable for in vitro culture of porcine pre-implantation embryos. Finally, at a zearalenone concentration level (250 μg/ml medium) found to cause degeneration of murine blastocysts, the in vitro maturation of bovine oocytes in Tissue Culture Medium 199 was not affected. It was suggested that the surrounding cumulus layer acts as a barrier to prevent the mycotoxin from directly acting on the oocyte. / Land and Food Systems, Faculty of / Graduate

No description available.

M.Tech. / A study to determine the occurrence of fungi and their mycotoxins in rural food and their effect on human health was carried out at N’wamitwa (Tzaneen), a rural area of Limpopo province (South Africa). Fifty-eight maize and twenty-nine bambara nuts samples were collected from selected house holds and taken to the storage facilities of the Food, Environment and Health research group (FEHRG) laboratory at the University of Johannesburg for analysis. The samples were analysed for moisture content, fungal infestation, mycotoxin contamination and their toxicity. The moisture content of the samples were at a range of 3-20% moisture. Fungi which included species of the genus Aspergillus, Fusarium and Penicillium were detected at all moisture ranges but more dominant in samples with higher moisture levels. Fungi in this study were able to produce mycotoxins which included deoxynivalenol (DON), zearelenone (ZEA), aflatoxins (AFs), T2- toxin, fumonisins (FBs), ochratoxin A (OTA) and citrinin. The most dominant toxins in maize samples quantified by VICAM were AFs followed by DON, FBs and lastly ZEA and in bambara nuts were FBs followed by DON, AFs and ZEA. HPLC was able to detect higher concentrations of FBs than VICAM. The toxins were then tested for their toxicity using human lymphocytes and the most toxic was DON followed by AFs, FBs and lastly ZEA. Three vials of the same toxin with different concentrations, one with the highest and others with the middle and the lowest concentrations were used to treat the human lymphocytes.

M. Tech.

Mycotoxins are secondary metabolites of fungi, which may contaminate animal feed and human food at all stages of the food chain. This has become a global concern and considered an important risk factor mostly for human and animal health. The aim of this project was to elucidate the general health and productivity of domesticated animals in selected rural areas of the Limpopo Province in relation to fungi and mycotoxin and find out possible solutions to avoid in the future further exposure and to improve animal production in rural areas. A total of 95 animal fresh faeces (50 from Mapate and 45 from Nwanedi districts), 50 feed samples (24 from Mapate and 26 from Nwanedi) and 50 fresh milk samples from cattle and goats were screened for fungi and mycotoxin contamination. The multi mycotoxin extraction method was used, followed by thin layer chromatography, also the VICAM immunoaffinity clean up, high performance liquid chromatography, gas chromatography mass spectrophotometry and the ELIZA enzyme linked kit method were used for further mycotoxin determination and quantification. The results obtained from this study revealed that species of Aspergillus, Fusarium and Penicillium fungi contaminated both feed and animal faeces samples. The species Aspergillus niger, A. clavatus, A. flavus, A. fumigatus, Fusarium verticillioides, F. graminerium and F. proliferatum were the most prevalent fungi. Fumonisin B1 and B2, aflatoxins B1, zearalenone and deoxynivalenol (DON) were found in animal feed. Fumonisins B1 and B2 were also found in faecal samples which indicated animal exposure to these mycotoxins. Cattle were the most exposed as compared to goats and pigs. In addition, aflatoxin M1 and traces of fumonisin B1 was detected in cattle and goats milk samples collected from both Mapate and Nwanedi districts. Late harvesting and poor handling of crops during storage seemed to be the reason for the results indicating feed contamination with high levels of fungi and mycotoxins. Daily exposure to this contaminants may influence or/and induce several symptoms such as dermatosis, immunosupression, liver and oesophageal cancer in both animal and human being. There is an urgent necessity to teach rural populations simple and cheap methods of crops storage and techniques to prevent feed and food contamination. / Prof. Mike F. Dutton Mr. F. Eric Van-Zyl

Maize (Zea mays L.) is an important cereal world-wide, serving as seed for growers, food for man and livestock as well as an industrial raw material. Unfortunately, it is also a suitable substrate for growth, development and activity of spoilage fungi. Fungal growth is a major problem in cereal grains throughout the world and may lead to poor quality of the products, as well as adverse effects to human and animal health due to mycotoxin production. Maize is usually harvested at high moisture content and then dried to bring down the moisture content to a safe level before storage. Delay in drying to safe moisture levels increases risks of mould growth and mycotoxin production. In rural villages maize is dried using only sun drying and they rely on sacks, thatched silo and drums as their storage facilities. This is insufficient to prevent damage by insects, rain, and rodents, which in turn allows fungi to invade these storage facilities. Maize was sampled in two rural areas of Venda (Limpopo Province) and the percentage moisture content was determined and then screened for total fungal contamination. The samples were also analysed for mycotoxins that have been reported to commonly occur in maize. There was no significant difference in the extent of fungal contamination in Mapate and Folovhodwe villages. Of the fungal species detected, Aspergillus species were the most common with Aspergillus flavus being the most predominant. On analysis by the multi-mycotoxin screen, aflatoxin had the highest incidence amongst mycotoxin, followed by T-2 toxin. However on using the VICAM method of analysis aflatoxins, deoxynivalenol and fumonisin were the most predominant mycotoxins in the samples, while zearalenone toxin was also amongst predominant mycotoxins but with the highest level of 0.1 ppm. Most of the mycotoxin-containing extracts were found to reduce the % cell viability of human lymphocytes, after 24 hours of incubation as determined by the methyl thiazole tetrazolium salt assay. vii In conclusion the co-occurrence of these toxins in maize and maize meal may highlight the problems associated with the intake of numerous toxins that could in turn lead to more adverse health effects such as liver, oesophageal, breast and cervical cancer, male reproductive tract damage and gynacomastasia. There is, therefore, need to disseminate information to these people, using simplified methods such as programs on radio and televisions on mycotoxin hazards and discussion on the issue should also feature regularly on daily newspapers and magazines, about the dangers and management aspects of mycotoxins, and the susceptible produce. / Prof. M. F. Dutton Mr. F. E. van Zyl

M. Tech. / Fusarium species are common contaminants of maize and are also capable of producing mycotoxins, in particular the fumonisin. These are implicated in animal and human mycotoxins fumonisin B1 (FB1) for example, has been associated in the aetiology of oesophageal cancer in South Africa and other parts of the world, i.e., China and Iran. Because maize is the staple diet of the South African rural population, this study was designed with the aim of monitoring Fusarium spp. and FB1 in the food of rural people of Venda, Limpopo province of South Africa, during the course of processing maize into porridge which gave a means of estimating dietary exposure to this mycotoxin. Measurement of fumonisin in the excreta of these people allowed a determine of the extent to which FB1 the body is actually exposed to the mycotoxin.Fumonisin B1 has been identified as a major fungal contaminant on maize, especially in the home grown crops intended for human consumption. Thus the rural population of Limpopo Province is at high risk from FB1 exposure and it is therefore of importance to assess this exposure by the analysis of suitable samples.It can be seen that levels of FB1 in maize from Venda are quite high, as several of these samples had exceeded levels above 1750 μg/kg as recommended as maximum tolerance levels by theEuropean Commission. It is equally seen that a much higher proportion of this mycotoxin was destroyed by processing maize to porridge. And because porridge and other maize-based products are usually consumed on a daily basis, the low levels found in the present study must not be under-estimated, as such levels may accumulate over time and cause more severe chronic effects in humans. When setting daily tolerable levels of FB1 in foods in South Africa, it is imperative to take into account the food habits, especially those within the rural communities