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ABSTRACT

This study was carried out on the functional properties of flour produced from abacha (cassava) flour. Four varieties of cassava, namely: 91/02324, 97/4779, 98/2101 and NR87184 were processed into chips (30 x 2.0 x3.0 mm), ‘abacha shreds (0.80, 1.0, 1.6 mm thick) ‘abacha’ slices (0.5 mm x 60 mm) and gari. The mechanical properties of the products, the hydration kinetics of the chips and the ‘abacha’ shreds as well as the chemical, functional, rheological and sensory properties of the products were studied. The results show that gari from chips and fresh cassava roots were comparable in quality in terms of chemical and rheological properties although gari from dried chips was rated low in sensory attributes. Cassava variety NR87184 produced the least gel strength (soft dough) at a water temperature of 100 ⁰C. Generally, gari dough was found to undergo a thinning effect with increase in water temperature and volume. The rate of moisture uptake and the time in while the chips attained equilibrium moisture content varied with soaking temperature and cassava variety. High coefficients of determination (r² =0.9656-1.000) obtained correlating the experimental and predicted moisture uptake values for chips show that the Peleg’s equation can be used to model water uptake of cassava chips from all four varieties. The position (vertical/horizontal orientation) of the chips as well as the cassava varieties from which they were made affected the mechanical properties of the chips significantly (p<0.05). For single-stranded ‘abacha shreds and gari dough, the mechanical properties at the yield point differed significantly (p<0.05) from that at peak value. Production of ‘abacha’ slices using dried cassava chips significantly (p<0.05) lowered consumer acceptance of the product. Cassava variety 97/4779 produced the most acceptable product in terms of chemical and sensory properties. When 97/4779 was studied more concertedly for ‘abacha’ slice production, boiling, peeling and slicing produced the most acceptable ‘abacha’ slices. Boiling 97/4779 for 30 minutes and soaking for 16 hours produced ‘abacha with the highest protein (1.337%), while boiling for 30 minutes and soaking for 20 minutes produced ‘abacha’ with the highest fibre content of 1.49%. The least value of HCN (4.596mg/kg) was obtained when boiling time and soaking time were 75 minutes and 8 hours, respectively. Boiling affected the carbohydrate, ash, protein, fat and fibre contents of ‘abacha’ slices, while soaking time significantly (p<0.05) affected the protein, fat and fibre contents of ‘abacha’ slices made from 97/4779. The pasting properties of flour made from ‘abacha’ slices processed from fresh and dried chips of 91/02324 were higher than those made from other varieties. Its high peak viscosity of 399.54 RVU indicates its suitability for products that require high gel strength and high elasticity. ‘Abacha’ shreds of thickness 1.0mm produced the longest strands. However, consumers preferred ‘abacha’ shreds of thickness 0.8mm as meal and snacks. Variety 97/4779 and 98/2101 were most preferred for making ‘abacha’ shreds. 

 

CHAPTER ONE

INTRODUCTION

1.1 Background       

Cassava (Manihot esculenta Crantz) is one of the most important tropical root crops. It is a major source of dietary energy for more than 500 million people (Cerk, 1985).  The ability of the crop to survive and even thrive in adverse conditions and its high yield potential has endeared it to many farmers.  Cassava is a major staple food crop in Nigeria and supplies about 70% of daily caloric intake of over 50 million Nigerians (Oyewole and Odunfa, 1987).  In sub-tropical Africa, cassava provides caloric intake for over 200 million people (Purseglove, 1994). Nigeria is the world largest producer of cassava with over 34 metric tons of the crop annually (Adeniyi et al.,s1997).

Cassava roots are processed in order to increase the shelf-life of their products, facilitate transportation, detoxify the products, and make the roots more palatable by providing a variety of products that are convenient to prepare and consume (Handerson and Perry, 1981; Eckstein, 1980). There are different processing methods employed in cassava growing areas, which may include a combination of many of several procedures performed in specific sequences (Nweke, 1992).  They include, peeling, washing, crushing, sl icing, chipping, pulping, soaking, drying, toasting, fermentation, boiling and cooking.

Cassava is processed into different types of food and industrial products such as chips, gari, ‘abacha’, flour, ‘fufu’, pellets, starch, alcohol, glucose syrups etc.  It has been estimated that over 70% of the cassava harvested in Nigeria is processed into gari (Olayade et al., 1992). Gari is consumed in all parts of Nigeria across all social strata.  In addition to composite flour for bread making, cassava flour is used in the production of noodles, biscuits, ‘nri-oka’ (fufu from maize-cassava blends) and confectionary (Nweke, 2002; Adeniyi et al., 1997).

Despite the immense potentials of cassava for food and non-food industrial uses, its supply as raw material is epileptic due to poor keeping quality of the fresh roots after harvest (Wenham, 1995; Oyewole and Odunfa, 1990; Oyewole, 1997).  In Nigeria, the flour milling industries must, according to a recent regulation by the Federal Government, incorporate 10 % of cassava flour into wheat flour for bread making (Ukpabi, 2006).  The successful implementation of this policy and the ability to provide raw material to cassava based industries depend, to a large extent, on the ability to process significant quantities of cassava into intermediate shelf-stable forms such as chips and ‘abacha’ which can be converted into different uses as the need arises.

Dried cassava chips are pieces of dried roots the length of which do not exceed 6 cm and have starch content of 70 % or more (Asiedu, 1998; Okaka, 2005). Gari, another product of interest, is a granular product obtained by fermenting peeled and grated cassava root pulp for 24 to 72 hours and then frying/garifying the dewatered mash (Akinrele 1964; Onyekwere et al., 1989). ‘Abacha’ is a shredded or sliced dry or wet product, obtained by shredding or slicing boiled cassava roots, soaking the shreds for 8-24 hours in cold water and washing.  It is consumed as snacks or main meal in the Eastern States of Nigeria.

 

 

1.2 Statement of the Problem.

Despite the importance of cassava as a major source of calorie and raw materials for industries, it still does not have an adequate and safe storage system presently.  Onwueme (1978), Oluwole and Adeyemo (2001) observed that irregular and inadequate supply of raw materials are major obstacles to industrial processing and utilization of cassava.

Storage techniques for fresh cassava roots which include storage in trenches, the use of moist saw dust and rice hulls, and wrapping with polyethylene bags, have been reported (Etejere and Bhat, 1986; Ravi et al., 1996; Booth and Coursey, 1974).  All the techniques have serious limitations at the commercial level.  Traditionally, cassava roots are left in the ground after maturity and are harvested piecemeal, as the need arises.  This practice prevents the land from being used for other agricultural activities in addition to the tendency of the roots becoming fibrous and woody loss of extractible starch and other nutrients (Ingram, 1972; Doku, 1969).

In order to ensure regular supply of cassava as an industrial raw material, there is a need to process it into chips and ‘abacha’ which are shelf-stable intermediate products that can be converted into different products such as gari, flour, ‘abacha’, ‘fufu’ etc when needed.

Oluwole et al (2004) and Ekwu and Ugwuonah (2006) have demonstrated that gari of acceptable quality can be produced using chips.  However, they did not evaluate the engineering properties of the chips and products nor consider the varietal effects of cassava on the quality of the products.  Various studies have shown that the physicochemical, functional and other quality characteristics of products from cassava are significantly affected by varietal differences (Cabrera, 1986; Safo-Kanitanka and Owusu-Nipah, 1992).

Therefore, there is need to investigate the effect of variety and processing conditions on the physiochemical, mechanical and sensory properties of cassava chips, and gari made from fresh cassava, from chips and from ‘abacha’. Shreded ‘abacha’ is sold on the basis of volume. Fragmented ‘abacha’ attracts low economic value for the processor and high rate of material loss during handling, packaging and transportation.  In order to prevent or minimize fragmentation of the product under dynamic and dead loads, there is need to determine the maximum allowable load and other engineering properties of ‘abacha’ made from different cassava varieties.  This will provide the base-data for design of ‘abacha’ handling and packaging equipment.

Re-hydration of dried ‘abacha’ is an integral part of the preparation of the dried product into a meal. However, there is no information in the literature on water uptake during the soaking of cassava products such as ‘abacha’ and chips in relation to varietal factors. Evaluating hydration conditions in order to control and predict the process is vital since hydration governs subsequent operations and the quality of the final product (Hung et al., 1993; Turhan et al., 2002). Hence there is need for an in-depth understanding, description and quantification of hydration kinetics of ‘abacha’ and cassava chips under different soaking conditions. It is necessary to characterize hydration phenomena as a function of time and temperature for the products (Abu-Ghannam and Mekana 1997; Turhan et al., 2002).

 

1.3 Goal Of Study

The broad purpose of the study was to evaluate the functional properties of flour produced from abacha (cassava) flour

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1.4 The specific objectives of this research were to:

1. To evaluate the mechanical and hydration characteristics of the chips and abacha shreds, made from four varieties of fresh cassava.
2. To produce gari and abacha from dried chips and from fresh cassava roots and evaluate their chemical, functional amd sensory properties.
3. To investigate the effect of processing methods on the physico-chemical properties of ‘abacha’ slices.

1.5 Scope of the study.

This study covers the production of cassava chips and ‘abacha’ slices as intermediate products as the well as production of gari and ‘abacha’ slices from fresh and dry cassava chips. Two types of ‘abacha’ products, namely: slices and shreds were studied.

The hydration of the chips and ‘abacha’ shreds which is an important unit operation during processing of these products into foods was thoroughly examined. Since cassava is processed into ‘abacha’ through different methods, the effect of processing methods on the quality of the product was evaluated in details.

The investigation of engineering properties carried out in this study is limited only to the mechanical properties of the chips, ‘abacha’ shreds and gari. The chemical, functional, rheological and sensory properties were also studied.