THE CHEMICAL IDENTITY OF THE BIOACTIVE COMPOUNDS RESPONSIBLE FOR THE OBSERVED ANTIFUNGAL ACTIVITY.

CHAPTER ONE

1. 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).