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THE INFLUENCE OF PROCESSING METHODS ON THE PROTEIN AND CYANIDE CONTENT OF AFRICAN YAM BEAN (Sphenostylis stenocarpa)

ABSTRACT

Raw African Yam bean (Sphenostylis stenocarpa) was subjected to various processing methods Viz: steeping in water for 6 hr and then boiling for 10, 20, 30, minutes respectively (samples B); steeping in water for 12 hours and then boiling for 10, 20, 30, minutes respectively (sample C) and finally sample A was raw yam bean which served as control.  The entire sample was dry – milled into fine flours. The glycosidic cyanide, crude protein, ash, moisture, some functional properties and bulk density of the flours were analyzed from the results, protein and cyanide content of sample A (raw sample) are 25.20% and 72.23ml. results showed that the toasting, process gave the highest protein (24.12) with no trace of cyanide and it negatively affected the protein content of the samples reducing it from 25.20 to 17.57, 17.51(%) respectively. 12 hours soaking and few minutes boiling process negatively affected the protein content of the samples reducing it from 25.20% to 13.12, 12.78, 12.09 (%) respectively but have the strongest impact in covering the cyanide level from 72.23ml to zero respectively. Moisture content ranges from 400% - 14%, Ash ranges from 2.50% to 5.00%, water absorption ranges from 105g/ml to 290g/ml, oil absorption ranges form 0.98 – 1.95g/m. The bulk density showed 0.74g/ml – 0.88g/ml.

CHAPTER ONE

INTRODUCTION

African yam bean (Sphenostylis stenocarpa) belongs to the genera papilliona sec which is in the class known as Leguminousae (Okigbo, 1973). It is one of the neglected indigenous grain legumes in Nigeria. It is produced mostly in the eastern part of the country where it is consumed in different forms such as snacks, delicacy, man meal etc. It can be used for the fortification of other foods (Eke, 1997) In Nigeria, it has as many names as there are communities cultivating it. Some of the names are Okpdudu, Azam, Uzuaku, Ijiriji, Azara, Ahaja, Nzamiri, Odudu, Girigiri (Hausa), sese (Yoruba) and Nsana (Ibibio) (Ogbo, 2002).

The high protein content of African yam bean makes it an important source of protein in the diets of population groups of many tropical countries (Kon, 1979, Ekpen young and Borchers, 1980). In addition, the high protein bean flour fractions could be substituted for wheat flour to produce acceptable qualities of cookies breads and leavened doughs (Uebersax and Zabik, 1986; Nzereogu, 1993). It may also be consumed as porridge after cooking. The mature dry seeds can be used to prepare “moi - moi” and “akara” (Ezueh, 1973; Akoma, 1996). The African yam bean apart from being rich in protein also contains carbohydrate, fat and minerals (NAS, 1979).

A major constraint in the utilization of African yam bean is the different dehulling method. Traditionally, the dehulling method involves manual removal of the hulls from the individual soaked seeds. This method is quite laborous (labour intensive), time – consuming and does not favour effective utilization of the bean. It is widely believed that under cooked African yam bean seeds cause diarrhoea and over cooked seeds cause constipation (Asusu and Undie, 1986). Previous works showed that steeping will among other things improve the dehulling characteristic of the African yam bean while maintaining the nutritional quality viz: invitro protein digestibility and also improving the functional properties when processed into flour (Abbey and Berezi, 1988). It is evident that better processing methods will not only enhance the acceptability and utilization of this legume but will also improve the nutritional status of the consuming populace (Uebersax et al, 1989).

The overall objective of this study is to investigate the various processing methods and their effects on the protein and cyanide content of African yam bean in conclusion, before the commencement of any research or project, there is meant to be aim/aims of such research.

As such, the aims of this study include:-

1. To determine the hydrogen cyanide content of the flour.

2. To analyse for the crude protein content of the flour.

3. To determine some of the functional properties of the flour.

4. Determination of the chemical composition of the flour.

5. To determine the bulk density of the flour.

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