Effect of Heavy Metals on Fermented Cassava

1.1 Introduction

Cassava (Manihot esculenta) is an extensively cultivated tuber crop and a staple food for millions of people in the tropical regions of Africa, Latin America and Asia. Globally, in terms of annual production, it is the fifth most important food crop after maize, rice, wheat and potato. Despite all the usefulness of cassava, its use as a food source is limited by its perishability, its low protein content and its potential toxicity. Cadmium (Cd), chromium (Cr) and lead (Pb) are the heavy metals of most concern because they can affect human health even in small quantities. In addition, Atafar et al. (2010) were also observed that application of some non-heavy metal fertilizers can potentially increase concentrations of Cd, Cr, and Pb in plants.

Cassava contains two cyanogenic glucosides, linamarin and a small amount of Lotaustralin, which are catalytically hydrolyzed to release toxic hydrogen cyanide (HCN) when tine plant tissue is crushed. Several varieties of cassava have been identified and grouped into bitter and sweet depending on the quantity of Linamarin in the tuber. The consumption of cassava and its derived products which contain Large amounts of HCN may be responsible for such visible manifestations as goiter and cretinism, tropical ataxic neuropathy (Bradbury, 2004).

As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the study. Others are Significance of the study, Scope of work, Limitations of the Study and Definition of technical terms.

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1.2 Background of Study

Cassava flour production till date is carried out at local levels mostly by local women who do so to enhance household food security (Fapojuwe, 2008), and according to Nweke et al. (2002), production of cassava flour remains labour-intensive. Large scale production of cassava flour in Nigeria failed probably due to the limited information on processing variables that promote detoxification in cassava, and fermentation to produce unique flavor characteristics associated with cassava flour (Achinewu and Owuamanam, 2001; Nweke et al., 2002).

Fresh cassava root contains a toxic compound (hydrogen cyanide), which is harmful for human consumption and apparently detrimental for the use of cassava in food industries (Iglesias et al., 2002). However, research have shown that processing techniques such as peeling, fermentation, soaking and drying can detoxify and reduce the cyanide content, improve palatability and add value to the root (Cardoso et al., 2005; Burns et al., 2012). Converting cassava root into food forms and raw materials such as fufu, cassava flour, tapioca, flour, chips and pellets can extend the shelf-life, facilitate trade and promote industrial use (Taiwo, 2006; Fadeyibi, 2012).

High quality cassava flour is white or creamy, unfermented and gluten-free flour obtained from cassava root and it is used in the food industry for the production of pasta and confectionery (Taiwo, 2006; Shittu et al., 2008). When wheat was substituted by up to 20% in bread, Eddy et al. (2007) found that cassava flour added no foreign odour or taste to the product formed and no significant changes were observed in other bread characteristics. The physicochemical properties of cassava flour offer the benefit of good functionality as raw material for the manufacturing of various food products. For instance, the high starch content of cassava flour contributes to crispy texture of processed products (Falade & Akingbala, 2010), while its low fat content is an excellent attribute for controlling rancidity and enhancing shelf-life stability of the product (Charles et al., 2005; Eleazu et al., 2011).

Accordingly, determining the available forms of heavy metals in soils is an important approach to the soil contamination assessment, especially in greenhouse areas which have great impact on environment and human health due to intensive use of fertilizers and pesticides containing heavy metals. The intensification of agricultural soil use, and changes in farming practice, characterized by intensive application of fertilizers and pesticides may cause soil pollution by heavy metals in greenhouses (Nouri et al., 2008). Namely, many chemical products used in agriculture, especially nitrogen and phosphate fertilizers, contain certain amounts of heavy metals, as result of their production from minerals used as a source of these elements.

Therefore, in Nigeria where the research was carried out, the activities that was conducted is to know the Effect of Heavy Metals on Fermented Cassava.

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1.3 Statement of Problems

Investigation revealed that in cassava food processing, it is often necessary to carry out trace element analysis to ensure that harmful and non-essential elements are kept at low concentrations as much as possible. Most of these ions are toxic to human beings by interfering with enzyme functions while some may have stimulatory effects. When the metals intake is at low concentration, the body system might not be able to remove it and it will remain in the body as impurities for a short time.

The increase of cyanide and some metal toxicants in cassava flour can cause toxic effects for consumers. The gravity of toxic effect depends on the nature, quantity, chemical form on body resistance and on synergetic or antagonistic effects of other chemical contaminants. Sometime in 2008, it was widely reported about a family who was nearly wiped out after eating food prepared from fermented cassava flour in Ondo state. Such food poisoning could result from pollution by known and unknown toxicants.

It is difficult to understand how cassava and cassava products such as cassava flour can be promoted without giving proper consideration to the fact that it contains cyanogens (linamarin) that liberates poisonous cyanide in the body. Consumption of cassava and its products containing amounts of cyanide can cause acute intoxication, with symptoms of dizziness, headache, nausea, vomiting, stomach pains, diarrhea and sometimes death (Oluwole et al., 2003).

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1.4 Aim and Objectives of Study

The aim of the study is to investigate the Effect of Heavy Metals on Fermented Cassava. In achieving this aim, the following specific objectives were laid out as follows:

1. To examine the concentration of total and available forms of heavy metals (Ni, Cr, Cu, Zn, Pb and Mn) in the greenhouse soils as well as the distribution of heavy metals in Cassava.
2. To examine the dietary exposure to heavy metals through consumption of cassava flour and create public awareness;
3. To estimate the rate of heavy metal in some cassava varieties;
4. To monitor the cassava fermentation time for breakdown and removal of heavy metal; and
5. To find out if there is any significant differences in the concentration levels of heavy metals in fermented cassava flour sourced from urban and rural areas of these states.

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1.5 Research Questions

The study came up with research questions so as to be able to ascertain the above stated objectives. The specific research questions for the study are stated below as follows:

• What is the concentration of total and available forms of heavy metals (Ni, Cr, Cu, Zn, Pb and Mn) in the greenhouse soils as well as the distribution of heavy metals in Cassava?
• What is the dietary exposure to heavy metals through consumption of cassava flour and create public awareness?
• What is the rate of heavy metal in some cassava varieties?
• What is the cassava fermentation time for breakdown and removal of heavy metal?
• What are the differences in the concentration levels of heavy metals in fermented cassava flour sourced from urban and rural areas of these states?

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1.6 Research Hypothesis

In order to pursue the objective of this study, the following generalized statements have been designed to guide and aids in obtaining the result for the experiment to be conducted. For this work, the null hypothesis will be represented with H0 while the alternative hypothesis will be represented with hypothesis H1.

Hypothesis One

• H0: There are no significant differences in the concentration levels of heavy metals in fermented cassava flour sourced from urban and rural areas of these states.
• H1: There are significant differences in the concentration levels of heavy metals in fermented cassava flour sourced from urban and rural areas of these states.

Hypothesis Two

• H0: There is no significant effect of fermentation time for breakdown and removal of heavy metal in Cassava
• H1: There is significant effect of fermentation time for breakdown and removal of heavy metal in Cassava

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1.7 Significance of Study

The relevance of the study will help ascertain the risk to public health owing to the fact that fermented cassava constitutes one of the major staple foods in Nigeria. The study will make people to know the inherent dangers of consumption of cassava flour and other food products that may contain heavy metals above the W.H.O (World Health Organization) guideline or permissible level.

This study will also be of immense benefit to other researchers who intend to know more on this study and can also be used by non-researchers to build more on their research work. This study contributes to knowledge and could serve as a guide for other study.

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1.8 Scope of Study

The scope of this research is focused on the Effect of Heavy Metals on Fermented Cassava in Nigeria.

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1.9 Limitations of the Study

During the course of this study, many things militated against its completion, some of which are:

1. Time Constraint: The time frame given to accomplish this project was very short due to school academic calendar and it was carried out under pressure which made the researcher not to implement some necessary features.
2. Research material: availability of research material is a major setback to the scope of the study.
3. Frequent power failure: This made the researcher append more money on fuel to ensure sustainable power.
4. Financial Constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet).

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