ABSTRACT
This work was aimed at determining the occurrence of aflatoxin producing fungi in three (3) foods: Rice (Oryza sativa), Maize (Zea mays) and Groundnut (Arachis hypogaea) sold in and around Umudike, Abia State, Nigeria. Samples were randomly collected from sellers in three (3) different markets (Umudike, Ahiaeke and Amawom). Serial diluted samples were plated on saboraud dextrose agar using spread plate methods and incubated at 250C for five (5) days, after which fungal growth and mycotoxin production were evaluated using standard method. Results obtained showed the presence of five (5) fungal species: Aspergillus niger, Aspergillus flavus, Penicillum species, Fusarium species and Yeasts. Fungal isolates showed varied occurrence: Aspergillus niger (88.9%), Aspergillus flavus (66.7%), Penicillum (66.7%), Fusarium (44.4%) and Yeasts (100%). The occurrence of A. niger in foods showed varying occurrence; rice (66.7%), maize (100%) and groundnut (100%), while A. flavus had 33.3%, 66.7% and100% in seeds respectively. The corresponding values for Penicillum were 33.3%, 100% and 66.7% whereas Fusarium recorded 0%, 33.3% and 100% for the same seeds. Yeasts were present in all the samples (100%). The gross occurrence of aflatoxin detected in foods were: maize (22.2%), groundnut (22.2%) and 0% in rice. The quantitative analysis shows Aflatoxin content ranged 37.76µg/kg to 60.72µg/kg with mean values of 39.80% in maize and 57.01% in groundnut. The variations in the occurrence of fungi, detection of aflatoxin in the seeds and the concentrations of aflatoxin in the foods were noted and it was observed that consumers of these foods are exposed to potential harmful effects. More aflatoxins were in the groundnut than in the maize and rice. Based on the findings, it was therefore recommended that there should be public enlightenment on the incidence of mycotoxins in our foods presently and the high risk associated with it.
TABLE OF CONTENTS
Title
page i
Certification
ii
Dedication
iii
Acknowledgements
iv
Table
of contents v
List
of tables vii
List
of figures viii
Abstract
ix
CHAPTER ONE
1.0 Introduction 1
1.1 Aim and Objectives 3
CHAPTER TWO
2.0 Literature Review 4
2.1 Aflatoxin Producing Fungi 4
2.2 The Health Implications of Aflatoxins in
Humans and Animals 4
2.3 Food Grains that can be Contaminated with
Aflatoxin 6
2.4 Major Diseases (Disease Classification)
Caused by Aflatoxin Consumption 8
2.5 Factors favourable for the Occurrence of
Aflatoxins in Food Grains 10
2.6 Aflatoxin in Contaminated Maize 11
2.7 Possibilities of Maize Being Contaminated
by Aflatoxin Producing Fungi 14
2.8 Aversion of Aflatoxins in Maize 15
2.9 Aflatoxin Contamination in
Groundnut 17
2.10 Prevention of Aflatoxins in Groundnut 18
2.11 Aflatoxin in Rice (Oryza sativa) 19
CHAPTER THREE
3.0 Materials and Methods 21
3.1 Source of Materials 21
3.2
Sampling, preparations 21
3.2.1
Sampling and sample preparation 21
3.2.2
Media preparation 21
3.3 Isolation of fungi contaminants of the
seeds 22
3.3.1.
Characterization of fungi isolates 22
3.3.2.
Identification of fungi isolates 23
3.4 Determination of aflatoxin 23
3.4.1.
Extraction of aflatoxin 23
3.4.2
Preparation of thin layer chromatography plate 24
3.4.3
Detection of Aflatoxin 24
3.4.4 Determination of aflatoxin content 25
CHAPTER FOUR
4.0 Results 28
CHAPTER FIVE
5.0 Discussion, Conclusion and
Recommendation 33
5.1 Discussion 33
5.2 Conclusion 35
5.3 Recommendations 35
References 36
LIST OF TABLE
Table Title Page
1:
Aflatoxin
Content of Seed Foods in Umudike 32
LIST OF FIGURES
Figure Title Page
1:
Occurrence
of Fungi Isolates 29
2:
Detection of Aflatoxin in
Seeds 30
CHAPTER ONE
1.0 INTRODUCTION
We
are all concerned with the quality and safety of food. Harmful components in
plants derived foods may be manmade sources or from the activities of
microorganisms. Cereals and legumes are some of the foods consumed in most
parts of Africa and the world over (Chauvin et al., 2012). Rich in different nutrients such as carbohydrates,
proteins and vitamins, these cereals and legumes are also susceptible to fungal
infections both on growing fields and in stores (Piotrowska et al.,
2013; Pereira et al., 2014). Aflatoxins occurring in food commodities are
secondary metabolites of filamentous fungi, they are group of chemically
similar compounds that contaminate many crops in hot, humid climates.
Aflatoxins are natural contaminants in raw materials, food and feeds (Bosco and
Mollea, 2012). They are usually produced as metabolites by these microorganisms
(fungi) and are described as mycotoxins.
Aflatoxins
(Afs) are produced by the three main genera Aspergillus,
fusarium and penicillium during
crop growth, harvesting or storage. They are produced primarily by two species
of Aspergillus (A.flavus and A. parasiticus) fungus which are
especially found in areas with hot, humid climates. These metabolites may not
be necessary for the growth and development of the fungi, it could help them to
eliminate and compete with other microorganisms in the same environment.
Aflatoxins are highly toxic and carcinogenic substance and are produced and
deposited in a variety of agricultural products including cereals and some
legumes. According to Gorya et al.,
(2009), these toxins have carcinogenic and mutagenic properties as well as
nephrotoxic and hepatotoxic properties which altogether make them harmful to
both humans and animals. These fungi affects cereals notably peanuts, corn,
wheat and rice. Aspergillus and penicillium were reported as the most
dominant genera in the African peanut seeds.
PrH,
(2000) reported that the major naturally produce aflatoxins are aflatoxin B1,
aflatoxin B2, aflatoxin G1 and aflatoxin G2. A.flavus is ubiquitous favoring the aerial parts of plants (leaves,
flowers) and produces B aflatoxins. A.parasiticus
produces both B and G aflatoxins, is more adapted to soil environment and has
more limited distribution (EFSA, 2007). A.
bombysis, A. ochraceoroseus, A. nomius and A. pseudotamari are also aflatoxins producing species, but are
encountered less frequently. Aflatoxin B1 is the most common in food and
amongst the most potent genetoxic and carcinogenic aflatoxins, it is the most
important and toxic to human beings from the public health point of view. It is
the most toxic and potent carcinogen, teratogen and mutagen to human and
animals (Sweeney and Dabson, 1998; Shahidi, 2004; Seo et al., 2011), causing damage such as toxic hepatitis, hemorrhage,
edema, immunosuppression and hepatic carcinoma (Speijers and Speijers, 2004,
Peng and Chen, 2009; Woo et al.,
2011). Aflatoxin M1 and M2 were also isolated and identified as mammalian metabolites
of aflatoxin B1 and B2.
Due
to the fact that these crops serve as staple crops and are consumed on a daily
basis, concerns have grown recently on the possible occurrence of mycotoxins in
these crops and the implications of these mycotoxins on human and animal
health. This has led to the introduction of maximum tolerated limits for
mycotoxins in several foods and food products in various countries. Developing
maximum limits requires information about the toxicity and the occurrence of
mycotoxins in food (Wagacha and Muthomi, 2008). Reports show that contamination
of cereals with toxic producing microorganisms may occur before during or after
harvest especially during storage. Poor hygiene of handlers and their
environment in addition of high temperature and moisture are factors that aid
microbial contamination of cereal at post-harvest level and there are often the
situations in most African settings (Jackson et al., 2008). Researchers and public health personnel are in
agreement with the report of Ngeda et al.,
(2011) that there is need to for mycotoxin surveillance, because of their wide
occurrence in contaminated commodities. In line with the above assertions, this
project was undertaken to survey the occurrence of aflatoxins in some seed
foods sold in and around Umudike (a university community) as one way of
determining the potential dangers to which consumers have are exposed.
1.1 AIM AND OBJECTIVES
The
aim of this project was to determine the occurrence of aflatoxin producing
fungi in three foods, Rice (Oryza sativa),
Maize (Zea mays) and Groundnut (Arachis hypogaea) sold in and around Umudike.
The
objectives of the study include the following:
1. To
isolate and identify fungi in the three test foods.
2. To
screen the fungal isolates for their ability to produce aflatoxins.
3. To
determine the relative occurrence of the fungi that produce aflatoxin in the
foods.
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