EFFECT OF PROCESSING ON THE CHEMICAL, FUNCTIONAL AND ANTI NUTRITIONAL PROPERTIES OF AFRICAN YAM BEAN (AZIMA)

African yam bean (Sphenostylisstenocarpa) is an underutilized food legume crop in the tropics that is not as popular as other food legumes crop (Moyib et al., 2008). 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)

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, Ekpenyong 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 dough (Uebersax and Zabik, 1986; Nzereogu, 1993). African yam bean is rich in vitamins (vit B2) and minerals such as potassium, phosphorus, magnesium, calcium iron and zinc but low in sodium and copper (Edemet al., 1990).

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).African yam bean represents a less expensive source of dietary protein than soya bean among Nigerians of low economic status and very little is known about its nutritional potential (Apata and Ologhobo 1990) when compared to available information with other types of bean. Several methods such as cooking, (Ogbonna, Soraki and Achinewhu; 2001), roasting (Aletor and Ojo 1989) etc.; can significantly detoxify and improve the functional properties of African yam bean seeds.Functional properties (water and oil absorption capacities, emulsification, nitrogen, solubility, wettability, foam stability, slurry viscosity and gelation) of legumes are determined to know the potential food uses of their flours.

Food processing of such food has aided easy digestion of foods. It also leads to improvement of taste and flavor. Taste and flavor play a key role in the acceptability of any food. Generally, processing is aimed at enhancing colour, brightness, consistency, viscosity etc. It is widely believed that under cooked African yam bean seeds causesdiarrhea and over cooked seeds cause constipation (Asusu and Undie, 1986).

The seeds also contain Anti-nutrients like tannins, oxalic acid, hydrogen cyanide, saponins and phytic acid which could bind with metals and hinder the absorption of nutrients into the body and secondary metabolites.Many food processing techniques have been highlighted as possible means of reducing or totally eliminating the anti­-nutrient levels that can be tolerated by animals particularly in monogastric nutrition (Fayusi and Aletor, 2005) and Man. Whatever methods adopted should ensure that African yam bean seeds should be detoxified to a considerable extent that reasonable quantity of seeds can be incorporated into diets of man and his animals.

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).

Since food processing has been reported to create changes in the anti-nutrient content and functional properties, this work seek to determine the effect of some processing steps on the chemical, functional and anti-nutritional properties of African yam bean flour.

1.1       OBJECTIVES:

Specifically the objectives of this work are

1.      To investigate the effects of processing steps such as fermentation and boiling under different condition on the chemical, functional and anti-nutritional properties of African yam bean flour.