presence of aflatoxins in smoked-dried fish sold in abeokuta, ogun ...

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CHAPTER TWO 2.0 LITERATURE REVIEW Aflatoxins are metabolites of Aspergillus flavus and A. parasiticus (Speare, 2005). The compounds are both toxic and carcinogenic to a wide range of animals. A review by Ciegler (1999), complete with bibliography, deals extensively with chemical properties, production conditions, and biological effects of the aflatoxins. A number of investigators have studied the formation of aflatoxins on human food. Marth (2000) observed aflatoxin production on Cheddar cheese and casein, which had been inoculated with A. flavus and A. parasiticus. Frank (2000) studied the production and diffusion of aflatoxins in apple juice, rye and wheat breads, and cheese by using a strain of A. flavus isolated from food. Wildman et al. (1992) inoculated a large number of sterilized and nonsterilized solid foods and fruit juices with A. flavus and obtained aflatoxins. Sterilized beef infusion and beef pieces supported yields of 15 and 11 jug of aflatoxin per g of meat, respectively, but no aflatoxins were produced on raw beef because of bacterial overgrowth. Frank (2000) obtained aflatoxins from A. flavus grown on a large number of foods including smoked fish, condensed and powdered milk, and egg noodles. Molds capable of producing aflatoxins are occasional contaminants of foods. Van Walbeek et al. (2005) found that 16 of 128 fungi isolated from74 food samples produced toxins when cultured on complex media and on shredded wheat. Molds often grow on meats, fish especially cured during storage or aging. Some of these molds have toxinogenic potential. Results obtained from a study carried out on the level of aflatoxins in smoked-dried fish in three markets in Uyo town, Akwa-Ibom State showed that Aspergillus flavus, Aspergillus tereus, A.fumigatus, Absidia sp., Rhizopus sp., Aspergillus niger, Mucor sp. Cladosporum sp., Penicillium italicum, Penicilium viridatus, Candida tropicalis and Fusarium moniliformis were found to be associated with smoked dried fishes sold in different market in Uyo. Aspergillus flavus and Aspergillus tereus, A. fumigates were the dominant mycoflora in decreasing sequential 9
order. Adebayo et al. (2006) reported similar result in marketed bush mango seeds (Irvingia spp.) stored for sale in Uyo. Penicillium viridatus, Candida tropicalis and Fusarium moniliformis occurred less frequently. The presence of A. flavus in the samples might probably make its consumption hazardous to health. According to Akande and Tobor, 1992 in artisanal fishery, freshly caught fish are covered with damp sacks and at times, they are mixed with wet grass or water weeds to reduce the temperature. Fish treated this way is prone to contamination with microorganisms such as bacteria and fungi. This indicates that spoilage of fish starts right from the aquatic ecosystem. Handling fishes are also prone to microbial attack especially in artisanal fishery due to unhygienic methods of reducing temperature. During the smoke drying period, smoking kilns used in artisanal fishery and the overloading of the fishes on the trays leads to improper processing which in turn encourages fungal attack (Eyo, 1992). During storage of smoked dried fish products, good storage practices are not adhering by wholesaler hence stores are not well ventilated and pest can easily gain access into the stores. The environment in which fishes are displayed in the market is not always hygienic and this is another avenue for microbial contamination. Very often, retailers display the smoked-dried fish samples in open trays beside the gutter on refuse heaps, this also encourages fungi attack and subsequent production of toxins. This is in agreement with the report of Akande and Tobor, 1992. 2.1 Fungi Producing Aflatoxins Aflatoxins are produced by the common fungi Aspergillus flavus and the closely related species A. parasiticus. These are well defined species: A. flavus produces only B aflatoxins and sometimes the mycotoxin cyclopiazonic acid (CPA), while A. parasiticus produces both B and G aflatoxins, but never CPA (Pitt, 1993). This simple situation, of just two aflatoxigenic species, has been complicated by more recent taxonomic findings. Kurtzman et al. (1987) described A. nomius, a species closely related to A. flavus but which produces small bullet-shaped sclerotia, as distinct from the large spherical sclerotia produced by many A. flavus isolates. This species is also distinguished from A. flavus by the production of both B and G aflatoxins (Saito et al., 2003). 10
Page 1 and 2: PRESENCE OF AFLATOXINS IN SMOKED-DR
Page 3 and 4: DEDICATION I dedicate this work to
Page 5 and 6: TABLE OF CONTENTS Title Page Certif
Page 7 and 8: CHAPTER THREE 3.0 MATERIALS AND MET
Page 9 and 10: LIST OF PLATES Plate 1: Ethmalosa f
Page 11 and 12: ABSTRACT This study was aimed to es
Page 13 and 14: foods, Nwokolo andOkonkwo (1998) fo
Page 15 and 16: Reactivity: The lactone ring is sus
Page 17 and 18: 1.1.4 Effect on Human Health Accord
Page 19: 1.1.7 Cellular Effects Aflatoxins a
Page 23 and 24: Aspergillus flavus and Aspergillus
Page 25 and 26: Peanuts, maize and cottonseed are a
Page 27 and 28: high proportion of endo-epoxide and
Page 29 and 30: of all mice, but the lesions were j
Page 31 and 32: The mean concentration of aflatoxin
Page 33 and 34: eported and concluded that there wa
Page 35 and 36: Table2: Analytical methods validate
Page 37 and 38: of regulations. Data were not avail
Page 39 and 40: CHAPTER THREE 3.0 MATERIALS AND MET
Page 41 and 42: 3.5 Test Procedure 1. The kit (cont
Page 43 and 44: CHAPTER FOUR 4.0 RESULTS 4.1 Sample
Page 45 and 46: Plate 5: Clarias gariepinus Plate 6
Page 47 and 48: Figure 1: Aflatoxin concentrations
Page 49 and 50: esult also revealed that Aflatoxins
Page 51 and 52: REFERENCES Abulu, E.O., Uriah, N.,
Page 53 and 54: European Commission (2002). Commiss
Page 55 and 56: Hull, J.E., Chen, Z.Y. and Eaton, D
Page 57 and 58: Peterson, S.W., Ito, Y., Horn, B.W.
Page 59 and 60: Wild, C.P., Yin, F., Turner, P.C.,
Page 61: APPENDIX II One -Sample T-test Test

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