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EFFECT OF FERMENTATION TIME ON THE QUALITY CHARACTERISTIC OF CASSAVA FLOUR

CHAPTER ONE

INTRODUCTION

BACKGROUND OF THE STUDY

Cassava (Manihot esculeuta Cranz) ranks fourth on the list of the main food crops in developing regions after rice, wheat and maize (Bokanga, 1999). Cassava is an important root crop in Africa, Asia and Latin America (Achi and Akomas, 2006), providing nutrition and energy for over 800 million people (Bokanga and Oto, 1994).

Cassava roots are potentially toxic due to the presence of high levels of cyanogenic glycosides linamarin, lotaustralin and anti-nutritional factor cyanide (Akinrele et al, 2000). Cassava contains 10 – 500 mg/Kg of roots, the value exceeding 1000 mg/Kg in some varieties (Aworh, 2008). Cyanogenesis is initiated in cassava when the plant cell is damaged. Rupturing of the vacuoles releases linamarin which is hydrolysed by linamarinase, a cell wall-associated glycosidase (Akinpelu et al., 2011). The linamarin content of cassava have been reported to be more than double during drought, leading to the outbreak of the disease called Konzo (Cardoso et al., 2005). More than 100 cases of the disease were reported during the drought of 2005 in Nampula and Zambezia provinces of Mozambique (Cliff et al., 2011).  Continuous ingestion of varying doses of cyanide from cassava products over time results in acute cyanide toxicity with symptoms of dizziness, headaches, diarrhoea, and sometimes death. Other symptoms include increased prevalence of goitre and cretinism in iodine deficient areas (Bokanga, 1999, Aworh, 2008). Children are more susceptible to cyanide poisoning since its lethal dose is proportional to body weight.

Cassava (Manihot esulenta crantz) constitutes one of the main staple foods in many sub-Saharan countries in Africa. Cassava is a significant source of calories for more than 500 million people world wide (cook 1985). It plays a food security role in providing a stable food base in areas prone to drought and famine. One main disadvantage of cassava is its rapid microbiogical determination occurrence (Sanni 1992). This cassava is processed into flour (cassava flour) and preserved.

Cassava flour is a fraction of cassava obtained from the roots. It is a good source of carbohydrates but a poor source of protein. Cassava flour differs from tapioca four in that tapioca is made from the cassava staunch of the cassava plant where cassava flour is the ground root. It is naturally glutten free. It is a good for bread, other baked food and celiac diet. Cassava flour is a good substitute for wheat flour. As a side note; insects will not eat cassava flour not even cockroach. Cassava flour may be fermented or unfermented.

Quality characteristics of cassava describes the properties and nutritional qualities/chemical characteristics of cassava flour which include the moisture content, protein content, fibre content, starch quality, cynagenic compounds present etc varying amount of these elements mentioned have been said to significantly reduce when the cassava flour is subjected to fermentation process.

Fermentation derived from the latin word feven meaning to be boiling. The best known example is the degradation of sugars in alcohol by yeast as exemplified in the spontaneous transformation of fruit juice into wine or cider with vigorous evolution of carbon (iv) oxide given the impression of boiling. The term is now used generally to describe metabolic process in which chemical changes are effected, not only on sugars but in many organic substrate by micro organism or derived enzymes. In food processing, fermentation is typically the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria or a combination of the two. Food fermentation has been said to serve five main purpose which include the enrichment of diet through development of a diversity of flavours, aromas and textures in food substrate, preservation of substantial amount of food through lactic acid, alcohol acetric acid and alkaline fermentations, biological enrichment of foods substrates with protein, essential amino acids, essential fatty acids and vitamins, elimination of antinutrients and a decrease in cooking time and fuel requirement. Natural fermentation proceeds human history. Since ancient times, however, humans control fermentation process.

Fermentation time describes the period allowed for the fermentation to take place. That is, the time allotted for fermentation to occur in a given food substrate.  

STATEMENT OF THE PROBLEM

Many processing methods have been developed empirically for reducing cassava toxicity in most cassava producing populations (Njoku and Obi, 2010). These processing techniques consists of a combination of procedures such as peeling, boiling, steaming, pounding, slicing, grating, roasting, soaking, pressing and fermentation (Hahn and Kersey, 1985). Fermentation is one of the oldest and most important traditional food processing and preservation techniques (Aworh, 2008). Natural fermentation of plant materials is widely used in under-developed countries to transform and preserve vegetables because of its low technology and energy requirements and the unique organoleptic properties of the final products (Daeschel et al., 1987).  During fermentation, endogenous linamarase present in cassava roots hydrolyses linamarin and lotaustralin releasing hydrocyanide (HCN). Crushing of the tubers exposes the cyanogens located in the cell vacuoles to the enzyme which is located on the outer cell membrane, facilitating their hydrolysis (Aworh, 2008). It has been reported that most processes to which cassava is subjected in preparation of food products lead to reduction in protein, vitamin and mineral content (Lancaster et al, 1982). Bokanga (1999) reported that protein is reduced by 50 – 87% in the preparation of food stuffs from cassava roots in Cameroon, while vitamin C, niacin and thiamine undergo considerable losses (Favier et al., 1971). However, Riboflavin levels has been found to be higher in fermented cassava products than in fresh cassava roots, thereby suggesting that fermentation leads to synthesis of this vitamin (Watson,1976).

OBJECTIVE OF THE STUDY

This study is aimed at investigating how different fermentation times influence the quality characteristics of cassava flour.

SIGNIFICANCE OF THE STUDY

In Nigeria, cassava has been processed into many fermented and unfermented products in many ways.  Some of the fermented products include cassava flour (Lafun) produced by drying and milling of fermented cassava tubers, cassava flakes (Gari) produced by grating, soaking, fermenting, roasting of cassava mash. Other products include fermented cassava slurry used to produce “Fufu”.

The quality of these fermented cassava products varies from one processor to the other and the length of fermentation employed. There is therefore need to document the effects of length of fermentation on these products. This work is focused on monitoring the changes in the composition of fermenting cassava mash intended for production of roasted cassava granules (gari) in order to determine the optimum fermentation period at which the maximum nutritive composition is achieved and to determine the fermentation time at which the hydrocyanide content is at a safe level.

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