ABSTRACT

Fresh peeled and grated cassava mash was blended with toasted African yam bean seed flour (TAYBSF) in ratios of 95:5, 90:10, 85:15 and 80:20 w/w cassava : African yam bean seed prior to fermentation (PreGAF samples) and after fermentation (PoGAF samples). Gari without African yam bean seed flour served as the control. Fermentation was done for 2 days after which the samples were dewatered. The dewatered samples were sieved, toasted and evaluated for chemical composition and functional properties. The level of TAYBSF and stage of inclusion had significant (p < 0.05) effect on the composition and functional properties of the samples. The PreGAF samples had higher chemical constituents than the PoGAF samples. Addition of TAYBSF led to an increase in the protein content of PreGAF samples from 2.60 to 13.74 %, crude fat from 0.52 to 0.79 % and the ash content from 0.47 to 1.91 %. Addition of TAYBSF also led to an increase in the crude protein content of PoGAF samples from 2.60 to 12.07 %, crude fat from 0.52 to 1.25 % and the ash content from 0.47 to 1.67 %. The total amino acid (TAA) content of PreGAF and PoGAF samples were significantly (p < 0.05) higher than that of the control sample with values ranging from 59.83 to 78.74 g/100g  and 58.04 to 66.34 g/100g for PreGAF and PoGAF samples respectively while the control sample had a TAA content of 55.83 g/100g. The total essential amino acid (TEAA) content of PreGAF samples increased from 25.64 to 35.62 g/100g while that of PoGAF samples increased from 25.64 to 30.30 %. The anti-nutrient (hydrogen cyanide-HCN) content of PoGAF samples slightly increased from 0.0460 to 0.1020 mg/100g while the HCN of PreGAF samples increased from 0.0460 to 0.0750 mg/100g with increase in the level of inclusion of TAYBSF. Increasing the level of TAYBSF addition increased (p < 0.05) the bulk density of PreGAF samples from 0.56 to 0.71 g/cm3 and in PoGAF samples from 0.56 to 0.67 g/cm3 but caused significant (p < 0.05) reduction in the water absorption capacity from 475 to 276 % and from 475 to 320 % for PoGAF and PreGAF samples respectively. The peak viscosities of the samples were reduced from 1370 to 153 cp in PreGAF and from 1592 to 1206 cp in PoGAF as the level of TAYBSF addition increased while the control sample had a peak viscosity of 2264 cp. Acceptability of the fortified samples decreased (p < 0.05) with increase in the level of addition of TAYBSF. Samples fortified with the lowest level of TAYBSF after fermentation (PoGAF5) compared favourably with the control sample in appearance, flavor, texture, mouldability and general acceptability with sensory scores of 7.33, 6.70, 7.03, 6.97 and 7.10 respectively. Samples that were fortified post fermentation with the lowest level of TAYBSF were most preferred by the panelists.                                                                                                                                                                                                                                                                                                                                  

     CHAPTER ONE

INTRODUCTION

1.1 Background of study

      The search for solution to malnutrition problem in its various forms particularly in developing countries necessitated the enhancement of nutritive quality of staple foods through improved processing, enrichment and fortification. “Gari” (toasted cassava meal) is one of such basic staples that demand attention considering its position in the dietary regime of a developing country like Nigeria (Okafor, 1992).

      Gari is a fermented, dewatered and toasted starchy granule from cassava which is widely consumed all over West Africa and in Brazil where it is known as ‘farinha de manioca’ (Lancaster et al., 1982). Gari is one of the most popular forms in which cassava (Manihot esculenta Crantz) also known as manioc is consumed in Nigeria and some other parts of West Africa (Kordylas, 1990). It is a major component of everyday diet in Nigeria providing about 11.835kJ/person/day (Osho, 2003). Traditionally, it is produced by pressing the juice out of peeled, grated cassava roots and allowing a natural lactic acid fermentation to take place for 2-5 days. The fermented mash is then toasted in an open aluminum pan over open fire until the starch gelatinizes and the moisture content reduces to less than 12% dry basis (Chuzel et al., 1986).

      Cassava from which this important staple is produced is low in protein and deficient in essential amino acids. The crude protein content of locally produced gari vary between 1.03 %    -2 % and the level of cyanide  vary from 0 to 32mg HCN equivalent Kg-1 depending on the cassava variety and processing method (Oke, 1994; Ojo and Deane, 2002). Gari has been shown to be a rich source of energy but of poor protein source (1.03 %) compared to other food groups like grains (FAO, 1997). Gari has low levels of methionine, tryptophan, lysine and phenylalanine (Okigbo, 1980). High protein foods of animal origin such as meat, fish, milk and eggs are very expensive especially for the low income earners who are in the majority among the population of West African sub-region. Although efforts to increase the local production of these animal protein sources to make prices affordable are still ongoing (Akerele, 1967), fortification of gari with plant protein may be another alternative. There is therefore, need to search for cheaper but good quality protein sources that are readily available (Oluwamukomi, 2008). Gari is never eaten alone as a full meal but is rather taken with vegetable stew that can provide other nutrients like protein (Obadina et al., 2006). However, the exorbitant cost of animal protein for low income earners deters the inclusion of such animal protein source in the soup that gari is eaten with. This fact makes the need to improve the protein quality of gari imperative (Osho, 2003; Oluwamukomi et al., 2005). It is therefore, logical to source protein fortificants from plant sources like African yam bean, soybeans, cowpea and bambara nuts among others.  African yam bean unlike other afore mentioned plant protein sources has not found uses in many food formulations as soybean hence it is said to be unexploited. African yam bean as one of the ideal plant protein sources for protein supplementation of starchy foods has been proposed because it will also help to extend the use of lesser known and underutilized legumes in a number of food preparations especially in the developing countries for human consumption (Nwokeke et al., 2013).

      The African yam bean [Sphenostylis stenocarpa (Hochst. Ex A. Rich) Harms] is a climbing legume adapted to lowland tropical conditions. It is one of the lesser-known legumes (Apata and Ologhobo, 1990) and widely cultivated in the southern parts of Nigeria. Nigeria produced about 3,424 tonnes of African yam bean in 2010. Like most grain legumes cultivated in Africa, African Yam bean is rich in protein (19.5%), carbohydrates (62.6%), fat (2.5%), vitamins and minerals (Iwuoha and Eke, 1996). The protein is made up of over 32 % essential amino acids, with lysine and leucine being predominant (Onyenekwe et al., 2000). African yam bean is a cheaper protein source than animal products such as meat, fish, poultry and egg – therefore it is consumed worldwide as a major source of cheap protein especially in developing countries where consumption of animal protein may be limited as a result of economic, social, cultural or religious-factors (Olayide, 1982). This work therefore seeks to determine the extent to which AYBS (African yam bean Seeds) can improve the nutrient quality and acceptability of AYBS containing gari.

1.2 Statement of problem

      Cassava tubers consist almost entirely of starch and are particularly low in protein (about 1-2 %), so dependence on cassava diets may lead to serious protein deficiency problems. Gari is never eaten alone most times as a full meal but is rather taken with vegetable stew/soup/sauce that can provide other nutrients like protein. However, the exorbitant cost of animal protein especially for low income earners deters the inclusion of such animal protein source in the stew that gari is eaten with. Improving the protein content of gari may be an alternative and affordable option. Fortification of cassava product like gari with plant protein is a viable affordable alternative to tackle specifically the problem of protein energy malnutrition in those areas affected by malnutrition. This plant protein can be sourced from unexploited indigenous legumes with high protein content (18.1 to 25.8 %) like African yam bean seeds

1.3 Justification       

      Gari, a major staple is low in protein (1-2 %) and dietary dependence on it can lead to long term severe protein malnutrition. Such malnutrition problem has been reported among consumers that rely primarily on gari and other cassava products as major food source with little or no high-protein food sources as complements. African yam bean seed is an indigenous legume rich in protein unexploited and can be used to complement this carbohydrate dense staple.

1.4 Objectives of the study

      The broad objective of this work was to improve the protein content of gari by inclusion of

toasted African yam bean seed flour and to assess the effects of the bean flour inclusion on the quality and acceptability of the gari.

Specific objectives were to:

I) Produce toasted African yam bean seed flour (TAYBSF).

2) Process gari from cassava tubers and incorporate different levels (%) of TAYBSF at pre- and post- fermentation stages.

3) Evaluate the chemical, functional and sensory properties of the processed gari.

1.5 Significance of the study

      This study addressed the problem of protein deficiency in gari, a major staple food, using food-to-food fortification approach and indigenous unexploited legume such as African yam bean seeds (AYBS). It is envisaged that this will enhance the protein content of gari, decrease the incidence of protein malnutrition among the less privileged gari consumers in Nigeria and other developing countries.

It is significant that the technology involved can be easily adopted domestically and at cottage level. Utilization of AYBS as gari fortificant will improve its production and accessibility and also diversify the use of this unexploited indigenous legume.

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