The aim of this study was to determine the effect of different processing methods on the chemical composition of African yam bean (Sphenostylis stenocarpa) flours and the organoleptic properties of it’s gruels. The seeds of cream coloured African yam bean (AYB) and lime were purchased from Oye Igbo-Eze and Ogige Nsukka markets, respectively in Enugu State, Nigeria.The seeds were sorted and divided into 4 equal portions of 1.5kg each. One portion was washed and fermented in tap water at a seed- water ratio of 1:3 (w/v), for 24h. The second portion was fermented in tap water (1:3 w/v) containing 30 tablespoonful of freshly squeezed lime for 24h. The third portion was fermented in tap water containing lime (30 tablespoonful of lime) (1:3 w/v) for 48h. They were separately sundried for 72h and roasted in a hot sauce pan until cracking. The fourth portion (control) was washed, drained and roasted in a hot sauce until cracking. The AYB samples were separately milled into fine flours and stored in separate airtight containers for chemical analysis and gruel preparations. The flour samples were chemically analyzed for proximate, phytate, tannins, oxalates, saponins, trypsin inhibitors, raffinose, stachyose, hemagglutinins and hydrogen cyanide composition using standard laboratory methods. A nine point hedonic scale was used to collect data on sensory and acceptability tests of the gruels. Means and standard deviations were calculated and least significance difference test was used to separate means. The sample that was fermented in tap water containing lime for 48h ranked best generally. The moisture levels for the flours ranged from 3.60-5.00%, protein 19.96-31.87%, fat 3.54-5.23%, ash 2.99-3.89%, crude fibre 4.00-6.01% and carbohydrate 52.72-62.32%. The anti-nutrient values for the flours were: phytate 2.63-2.97mg/g, tannins 0.02-0.04mg/g, trypsin inhibitors 0.45-0.53mg/g, oxalate 0.01-0.03mg/g, the samples had the same saponin level of 0.01mg/100g. Raffinose contents of the samples ranged from 8.25mg-9.22/100g and stachyose (8.48-6.76mg /100g). heamagglutinins ranged from 4.87 – 6.70 mg/100g and hydrogen cyanide ranged from 0.22-0.28mg/g. In the organoleptic studies, the sample that was fermented for 48h was most preferred over others in terms of colour (6.53), the sample that was fermented in lime water for 24h ranked best for flavor (6.57) and the sample that was only roasted ranked best for general acceptability (6.03).
1.1 Background to the study
It is of great importance to know the nutrient, toxic substance as well as the anti physiological substance composition and organoleptic properties of locally available foods in any community or country. Knowledge and use of local foods can help eliminate malnutrition. One of the problems of planning therapeutic diets with local foods is limited information on their nutrient composition (Standing Committee on Nutrition (SCN), 2006). It has been proposed that the fight against malnutrition in developing countries should be on the use of mixtures of tubers, cereals and legumes indigenous to them (Nnam, 2003).Urbanization has made people forget their traditional foods and favour convenient foods which are mostly nutritionally inadequate and expensive. The most dietary deficit is protein of high biological value and this was attributed to the high cost of animal protein (SCN, 2006). Vegetable proteins however complement each other if well chosen and will have a nutritive value as good as animal protein (Achinewhu & Akah, 2003; Nnam, 2003; Obiakor, 2008).
Nutrition is coming to the fore front as a major modifiable determinant of chronic diseases, with scientific evidence increasingly supporting the view that alterations in diet have strong effects (both positive and negative) on health throughout life. Dietary adjustments may not only influence present health, but may determine whether or not an individual will develop such diseases as diabetes, obesity, hypertension, certain cancer and cardiovascular disease much later in life (WHO/FAO, 2003). Rapid change in disease pattern had occurred as a result of shifts in diet and lifestyle. The urban based Nigerian is shifting from exercise, intense agrarian life to a more sedentary urban life, with resultant obesity, diabetes and hypertension. Cheap imported foods, global markets and socio-cultural changes are placing African traditional diets at distinct disadvantages. Indigenous diets are being replaced with more refined carbohydrate fast foods (Ifeyironwa, Eyzaquirre, Matig, & Johns, 2006). In tackling the multiple problems of food insecurity, nutrition transition and the double burden of diseases, it is essential to mobilize and employ indigenous foods like legumes as part of the solution (SCN, 2006). This is because several studies have reported immense nutritional and health protecting properties of African indigenous foods such as legumes (Obizoba & Souzey, 1989; Enwere, 1998; Ene-Obong & Carnovale, 1992; SCN, 2006; Okeke, Ene-Obong, Uzuegbunam, Simon, & Chukwuone, 2009).
For quite some time, legumes were considered not too important; but now, their food use is increasing with recent discoveries concerning their many nutritional and health properties (Pamplona-Roger, 2006).It has been documented that legumes contain 2-3 times the protein of cereal grains and no other plant food is as rich in protein as legumes in their natural state (National Academy of Science (NAS), 1997; Pamplona-Roger, 2006). Water soluble non-starch polysaccharides (NSP) that have viscous properties occur mostly in legumes and its benefit in the prevention/management of diabetes and cardiovascular diseases have been reported (Onyechi, Jude, & Ellis., 1998; Enwere, 1998). One such legume of interests is African yam bean (Sphenostylis stenocarpa) (AYB).
African yam bean (AYB) is an herbaceous leguminous plant occurring throughout tropical Africa (United States Department of Agriculture (USDA), 2007). It is grown as a minor crop in association with yam and cassava. AYB serves as security crop; it has the potential to meet year round protein requirements if grown on a large scale (World Health Organization (WHO), 2002). African yam bean (AYB) is highly nutritious with high protein, mineral and fibre content. Its protein content is reported to be similar to that of some major and commonly consumed legumes. Its amino acid profile is comparable if not better than those of cowpea, soy bean and pigeon pea (Obizoba & Souzey, 1989; Ene-Obong & Carnovale, 1992; Uguru & Madukaife, 2001). It has high metabolic energy, low true protein digestibility (62.9%), moderate mineral content, the amino and fatty acids contents are comparable to those of most edible pulses (Nwokolo, 1987; Uguru & Madukaife, 2000). It has a higher water absorption capacity when compared to cowpea (Achinewhu & Akah, 2003).
The potential role of AYB in the management of many aging and chronic non-communicable diseases has been reported (Enwere, 1998; Nwachi, 2007; Alozie, Udofia, Lawal & Ani, 2009). In Ghana, the water drained after boiling may be drunk by lactating mothers to increase their milk production (Klu, Amoatey, Bansa & Kumaga, 2001). The economic potential of AYB has been recognized, especially in reducing malnutrition among Africans (Adewale, 2010).
These health benefits can be marred by the presence of anti- nutrients. Some processing methods however, such as soaking, boiling, fermentation, roasting, among others are known to achieve reduction or elimination of the anti nutritional factors which affect the nutrients (Nnam, 1994., Nnam, 1995; Ene-Obong & Obizoba, 1995; Obizoba & Atti, 1994; Messina, 1999; Nnam, 1999).
1.2 Statement of the Problem
Studies have shown that inspite of the good attributes of AYB, it is underutilized and rarely consumed in urban and rural areas in Nigeria. Its current status as a minor crop means that its potential is largely unexploited. It faces the danger of extinction (Klu et al., 2001). The use of AYB may be limited by the beany flavour and long cooking time. These limitations can be overcome by processing like fermentation, soaking, roasting among others (Nnam, 1994; Ene-Obong & Obiziba, 1995; Nnam, 1999; Fasoyiro, Ajibade, Omole, Adeniyan & Farinde, 2006; Adewumi and Odunfa, 2009). Moreover, soaking or fermenting in lime medium can equally improve flavour, reduce the incidence of flatulence and acts as anti oxidant (OnlineFamilydoctors, 2000, Waladkhani, & Clemens, 2003; NewWorldencyclopedia, 2010). Citric acid treated AYB has been shown to have greater reduction in toxic substances like the cyanides (Azeke, et al., 2007).