CHAPTER ONE

INTRODUCTION 

1.1       BACKGROUND OF THE STUDY

Cassava (Manihot esculenta Crantz) is a tuberous root crop grown in the tropics between latitudes 30°N and 30°S, with low cost vegetative propagation. It belongs to the family of Euphorbiaceae and originated from South America (Nhassico et al., 2008). The root is drought resistant and capable of growing in different types of soil and seasons (Taiwo, 2006). As one major staple food in the tropical and subtropical region, cassava provides food for a population of more than 500 million across Africa, Latin America and Asia (Opara, 1999; Montagnac et al., 2009). The root, which is the major edible part of the crop, is rich in carbohydrates, and the starch content (86.49 ± 2.68%) is higher compared to other root and tuber crops such as yam (10.7 ± 1.1%), sweet potato (69.15 ± 5.85%), and taro (11.2 ± 1.26%) (Lebot et al., 2009). However, it is low in protein, fat, fibre as well as some vitamins and minerals (Charles et al., 2005). Utilisation of cassava root as a food source and as industrial raw material is limited because of the rapid postharvest deterioration which starts within two days after harvest (Sánchez et al., 2006; Opara, 2009; Iyer et al., 2010). This situation shortens the shelf-life of the root, leading to postharvest loss, low products yield and poor market quality of fresh root and minimally processed cassava food products such as cassava flour and flour (Van Oirschot et al., 2000).

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).

Globally, there is a notable increase in demand and price of cereals, especially wheat, which consequently influences the price of cereal-based products (FAO, 2013). The rising cost of importing wheat flour for food in many developing countries such as Nigeria has spurred the need for research to develop suitable flour from local agricultural materials such as cassava, which are cheaper but also possesses suitable quality attributes and functional properties. Furthermore, wheat flour contains gluten which causes celiac disease especially to gluten intolerant persons (Briani et al., 2008). Studies have recommended gluten-free diet as a suitable treatment for patients with celiac disease, gluten intolerance and wheat allergic reactions (Gaesser & Angadi, 2012; Alvarez & Boye, 2014). Therefore, non-wheat gluten-free flour developed from root and tuber crops such as sweet potato (Ipomoea batatas), cassava (Manihot esculenta), potato (Solamum tuberosum), yam (Dioscorea spp) and cocoyam (Xanthosoma sagitifolium) offer the potential to alleviate the double burden of rising cereal prices and gluten intolerance (Aryee et al., 2006; Ammar et al., 2009; Sanful & Darko, 2010). In particular, the use of gluten-free flour from high quality cassava root as composite flour in highly sought after foods such as bread has gained popularity in many developing countries (Eddy et al., 2007).

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). Flour and other materials used in manufacturing food products need to be packaged and stored properly prior to utilisation to ensure the quality, safety and storage stability. To realise the full potential of cassava flour in food processing, either alone or in combination with other raw materials such as wheat flour, knowledge of the effects of package types and storage conditions on quality and shelf-life stability of cassava flour is important.

1.2       PROBLEM STATEMENT           

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).

 Traditional processing of cassava by fermentation is centered on reduction of cyanide in the resultant product through extended period of fermentation for up to 7days as important strategy for the safety of product (Sanni, 2005). However, the traditionally processed cassava flour contain varied amount of residual cyanide because of the tendency by local processors to shorten the duration of fermentation in order to meet growing market demand (Nweke et al., 2002).

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). Since lethal dose is proportional to body weight, children tend to be more susceptible to outright poisoning than adults. In regions where there is iodine deficiency, which causes goiter and cretinism, cyanide intake from cassava exacerbates these conditions (Delange et al., 1994). In west Africa particularly Nigeria, there is a disease called tropical ataxic neuropathy (TAN), which generally occurs in older people who have consumed a monotonous cassava diet over years. TAN is progressive and causes unsteady walking, produces loss of sensation in hands, loss of vision, deafness and weakness (Dulcer et al., 2008). Until recently, long term cyanogenic intake was linked with the occurrence of TAN but recent work has shown that the situation may be more complex. Also, when cassava and its products are eaten, most of the ingested cyanide is converted into thiocyanate, a reaction catalyzed by the enzyme rhodanese, which uses up part of the pool of S-containing essential amino acids, methionine and cystein (Cardoso et al., 2004). These amino acids are essential in the diet because they can only be obtained from the food consumed. A shortfall of this S-containing amino acid would limit protein synthesis and could cause stunting in growing children, as was found in a study of children in DRC (Dulcer et al ., 2008).

 It is therefore the object of this work to note new methods of processing and technology towards reducing human cyanide intake.

1.3        OBJECTIVES OF THE RESEARCH

The main objective of this research is to study the effect of fermentation time on the quality characteristics of cassava flour. 

The specific objectives of this research work are as follows;

•           To produce cassava flour at controlled conditions of temperature, relative humidity    and time.

•           To monitor the fermentation time for breakdown and removal of cyanogenic compounds and cyanide.

•           To determine the proximate composition, functional and pasting properties of the final products.

•           To determine the sensory attributes of the products.

1.4       JUSTIFICATION 

There is need to optimize the local cassava flour processing methods as well as its industrialization especially by reducing the fermentation time and achieving the elimination of cyanide while maintaining cassava flour quality.  

 This present study considered the variability in the environment and fermentation conditions (temperature, relative humidity and duration of fermentation) during fermentation of cassava mash as they affect quality characteristics of cassava flour and reduction of cyanide.

1.5       SCOPE OF STUDY

This research work covered obtaining the samples, processing it (fermenting the cassava mash at different combined fermentation variables; temperature, relative humidity and time). The samples were analysed for pH, TTA and HCN. Thereafter, the samples were toasted to obtain the final product (cassava flour) which were analysed for proximate, chemical, functional, pasting and sensory properties. 

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