ISOLATION IDENTIFICATION AND CHARACTERIZATION OF FUNGI ASSOCIATED WITH THE SPOILAGE OF CORN

ISOLATION IDENTIFICATION AND CHARACTERIZATION OF FUNGI ASSOCIATED WITH THE SPOILAGE OF CORN

CHAPTER ONE

INTRODUCTION

1.0       Background Information on Corn

The natural forests of West and Central Africa are rich in resources, and have tremendous biodiversity (FAO, 1983), particularly in trees that provide food, fuel, fibre, medicines and various other products, including construction and building materials (Ladipoet al., 1996).

The tropical rainforests of West and Central Africa is the home to many native economically important trees such as the Irvingia species, namely Dent corn, and Flint corn(Harris, 1996; Lowe et al., 2000).

Maize has Scientific classification as; Kingdom-Plantae; Order-Poales; Family-Poaceae ;Genus-Zea; Species-Z. mays and its Binomial name is Zea mays.

Maize also known as corn, is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The leafy stalk of the plant produces separate pollen and ovuliferous inflorescences or ears, which are fruits, yielding corns or seeds.

Maize has become a staple food in many parts of the world, with total production surpassing that of wheat or rice. However, not all of this maize is consumed directly by humans. Some of the maize production is used for corn ethanol, animal feed and other maize products, such as corn starch and corn syrup. The six major types of corn are dent corn, flint corn, pod corn, popcorn, flour corn, and sweet corn.

Most historians believe maize was domesticated in the Tehuacán Valley of Mexico. Recent research in the early 21st century has modified this view somewhat; scholars now indicate the adjacent Balsas River Valley of south-central Mexico as the center of domestication.

An influential 2002 study by Matsuoka et al. has demonstrated that, rather than the multiple independent domestications model; all maize arose from a single domestication in southern Mexico about 9,000 years ago. The study also demonstrated that the oldest surviving maize types are those of the Mexican highlands. Later, maize spread from this region over the Americas along two major paths. This is consistent with a model based on the archaeological record suggesting that maize diversified in the highlands of Mexico before spreading to the lowlands.

Archaeologist Dolores Piperno has said:

A large corpus of data indicates that it [maize] was dispersed into lower Central America by 7600 BP [5600 BC] and had moved into the inter-Andean valleys of Colombia between 7000 and 6000 BP [5000–4000 BC].

— Dolores Piperno, The Origins of Plant Cultivation and Domestication in the New World Tropics: Patterns, Process, and New Developments. Since then, even earlier dates have been published.

According to a genetic study by Embrapa, corn cultivation was introduced in South America from Mexico, in two great waves: the first, more than 6000 years ago, spread through the Andes. Evidence of cultivation in Peru has been found dating to about 6700 years ago. The second wave, about 2000 years ago, through the lowlands of South America.

Before domestication, maize plants grew only small, 25 millimetres (1 in) long corn cobs, and only one per plant. In Spielvogel's view, many centuries of artificial selection (rather than the current view that maize was exploited by interplanting with teosinte) by the indigenous people of the Americas resulted in the development of maize plants capable of growing several cobs per plant, which were usually several centimetres/inches long each. The Olmec and Maya cultivated maize in numerous varieties throughout Mesoamerica; they cooked, ground and processed it through nixtamalization. It was believed that beginning about 2500 BC, the crop spread through much of the Americas. Research of the 21st century has established even earlier dates. The region developed a trade network based on surplus and varieties of maize crops.

Maize is the most widely grown grain crop throughout the Americas, with 361 million metric tons grown in the United States in 2014 (Production table). Approximately 40% of the crop—130 million tons—is used for corn ethanol. Genetically modified maize made up 85% of the maize planted in the United States in 2009.

Sugar-rich varieties called sweet corn are usually grown for human consumption as corns, while field corn varieties are used for animal feed, various corn-based human food uses (including grinding into cornmeal or masa, pressing into corn oil, and fermentation and distillation into alcoholic beverages like bourbon whiskey), and as chemical feedstocks.

 1.2       Statement of Research Problem

The fungal attack on post-harvest crops is quite alarming (Harris, 1996). These fungi of post-harvest crops, naturally produce mycotoxins which could constitute health hazard to the unsuspecting consumers (Cotty et al., 1994). These mycotoxins may remain in food long after the fungal source has died, and are hardly destroyed by cooking or freezing as mycotoxins can remain stable for up to 268 – 2690C (Frazier and Westhoff, 1988). Mycotoxins resist decomposition or being broken down in digestion, so it remains in the food chain (Mahendra et al., 2012).

Mycotoxins are quite numerous, among which are aflatoxins, Ochratoxins, Fumonisins, Zearalenone. Out of these, aflatoxins have assumed economic importance, because of their influence on the health of human beings and livestock, as well as the marketability of agricultural products. In most developing countries, limited or no facilities exist for monitoring these toxins in foods and feeds. Since aflatoxins are ubiquitous in the food and feeds substances consumed locally, there is therefore the need to monitor their levels so that they do not exceed the World Health Organization (WHO) standard for food samples, which is 20 ?g/kg (Oladejoh and Adebayo-Tayo, 2011).

 1.3       Research Objectives

The aim of this study was to isolate identify and characterize the fungal species that are associated with the spoilage of corn sold in some markets within Edo state. The specific objectives are;

1.         To determine whether the corn sold in some markets within Edo state are attacked by fungi.

2.         To isolate and identify the species of fungi attacking the corn from the markets

3.         To determine whether the fungal species identified were potentially aflatoxic

4.         To determine the aflatoxin concentration or level of the corn of the two species

 1.4       Research Question

The following research questions guided the study;

1.         Is the corn sold in some markets within Edo state attacked by fungi?

2.         What are the species of fungi isolated and identified to be attacking the corn from the markets?

3.         Are the fungal species identified potentially aflatoxic?

4.         What is the aflatoxin concentration or level of the corn of the two species

 1.5       Research Hypotheses

1.         The corn sold in some markets within Edo state are not infested with fungi

2.         The species of fungi infesting corn from the markets cannot be isolated and identified.

3.         The fungal species identified were not potentially aflatoxic

4.         The aflatoxin concentration or level cannot be determined.

 1.6       Significance of Study

Corn is widely consumed by man globally (Matos et al., 2009). The two species of corn are also valued for their health and medicinal benefits (Duguma et al., 1990; Ndoye et al., 1997; Van, 2010). Studies have shown that seed extract of the corn caused a significant reduction in body weight among obese people in Cameroon (Ngondi et al., 2005). These benefits therefore, make the market for corn very robust and economically valuable. Unfortunately, fungi that produce harzardous mycotoxins attack these corn, thereby making them potentially harmful to both man and livestock that consume them (Adebayo-Tayo et al., 2006; Iyayi et al., 2010). One major mycotoxin that fungal contaminated corn possess is aflatoxin (Wu and Khlangwiset, 2010). Aspergillus flavus and Aspergillus parasiticus have been implicated in the possession of aflatoxins (Rizzo et al., 2004), and in this work, Aspergillus flavuswas identified from the samples, including other fungal species that are potentially harmful.

For these reasons, the need to quantify the level of aflatoxin present in the cornsold in some markets in Edo is therefore imperative, as this would provide information on the safety of the corns for human and animal consumption. This research work, therefore, will be of great use to the public as well as the academia with the provision of information on this regard and contribution to the existing body of literature.

 1.7       Scope of Study

The study is focused on the Isolation, Identification and Characterization of Fungi associated with the spoilage of Corn, Edo state. The two types of corn considered were the Dent corn and Flint corn.