CHAPTER ONE
INTRODUCTION
Mycotoxins occurring in food commodities are secondary
metabolites of filamentous fungi, which can
contaminate many types of food crops throughout the food chain (Reddy et
al., 2010). Although, hundreds of fungal toxins are known, a limited number of
toxins are generally considered to play important roles in food safety
(Shephard, 2008; Reddy et al., 2010). Fungal toxins of most concern are
produced by species within the genera of Aspergillus, Fusarium and Penicillium
that frequently occur in major food crops in the field and continue to
contaminate them during storage, including cereals and oilseeds. Among these
mycotoxins, aflatoxin Bl (Arol), fumonisinBI (FBI) and ochratoxin A (OTA) are
the most toxic to mammals, causing a variety of toxic effects including
hepatotoxicity, teratogenicity and mutagenicity, resulting in diseases such as
toxic hepatitis, hemorrhage, oedema, immunosuppression, hepatic carcinoma,
equine leukoencephalomalacia (LEM), esophageal cancer and kidney failure
(Donmez-Altunta et al., 2003; Santos et al., 2001). The AFBI has been
classified as a class I human carcinogen, while FBI land OTA have been
classified as class 2B (probable human) carcinogens by the International Agency
for Research on Cancer (IARC, 20033). Several outbreaks of mycotoxicoses
diseases in humans and animals caused by various mycotoxins have been reported
after the.’ consumption of mycotoxincontaminated food. and feed (Reddy and
Raghavender, 2007).
Several strategies are used at controlling fungal growth and
the mycotoxin biosynthesis in stored grains by chemical treatments with
ammonia, acids and bases or with food preservatives by physical methods and by
biological methods. These methods require sophisticated equipment and expensive
chemicals or reagents. Use of natural plant extracts provides an opportunity to
avoid chemicals or reagents chemical preservatives. Over the years, efforts
have been devoted to search for anti-fungal materials from natural sources for
food preservation (Galvano et al., 2001). Several edible botanical extracts
have been reported to have antifungal activity (Reddy et al., 2009). The
essential oils extracted from clove have been shown to possess significant
antifungal properties (Reddy et al., 2007). The inhibitory effects of neem
plant extracts on mycotoxin biosynthesis have been examined (Reddy et al.,
2009). However, this study will review the developments in control
mycotoxigenic fungi and mycotoxins using plant extracts and plant oils to fill
the existing gaps and to develop effective antimycogenic natural products for
reduction of mycotoxigenic fungi and mycotoxins in foods.
Rice (Oryza sativa) is the most important food crop in
Nigeria and the bulk of rice is grown in wet season. Heavy rainfall and floods,
particularly near harvest, in coastal areas in eastern, southern, and western
regions of the country wet the crop and make panciles more prone to invasion by
Aspergillus flavus specie. Reddy et al (2004)
in a preliminary study, Aspergillus flavus isolated from rice grains were shown
to possess the ability to produce Aflatoxin BI (Reddy et al., 2005). However,
mycotoxin producing fungi is les commonly reported for rice than for many
cereal a crops (Tanaka et al., 2007). But rice represents a very good substrate
for fungal growth since it is used as an ideal culture medium to test the
toxigenic potential of isolated strains (Bars, 1992). Among the aflatoxins,
aflatoxins BI is the most toxic form for mammals and presents hepatotoxic,
teratogenic and mutagenic properties, causing damage such as toxic hepatitis,
edema, immunosuppression (Sperijers and Speijers, 2004).