EFFECT OF DIFFERENT PROCESSING METHODS ON THE CHEMICAL COMPOSITION OF AFRICAN YAM BEAN (SPHENOSTYLIS STENOCARPA) FLOURS AND ORGANOLEPTIC CHARACTERISTICS OF THEIR GRUELS

ABSTRACT

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).

CHAPTER ONE

1.0      INTRODUCTION

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).

Some studies have been carried out on the nutrient, anti nutrient and toxic substance composition of AYB and some of its products and processing methods to improve the food use (Ene-Obong & Obizoba, 1995; Nnam, 1997; Nnam, 2003; Omeire & Ogbonna, 2006; Onyechi and Nwachi, 2008). Little has been done on the effect of 24h fermentation with and without lim e, 48h fermentation in lime water and roasting to  address the beany flavour. Little has equally been done on the effects of these processing methods on nutrient, anti nutrients, toxic substances, anti physiological factors and other organoleptic characteristic of AYB flour and gruel.

There is the need therefore to determine the effect of 24h fermentation with and without lime and subsequent roasting, 48h fermentation in lime water and subsequent roasting on the chemical composition of AYB flours and organoleptic characteristics of their gruels.

1.3      Objective of the study

General objective

The general objective of the study was to determine the effect of different processing methods on the chemical composition of AYB flour and organoleptic characteristics of their gruels.

The specific objectives were to determine the processing methods on:

a.   the proximate composition of the flours;

b.   the anti nutrient composition of the flours;

c.   the raffinose,  stachyose,  hydrogen  cyanide  and haemagglutinin  contents  of  the flour; and

d.   the organoleptic characteristics of their gruels

1.4      Significance of the study

The study would provide information on the nutrient, anti-nutrient,  haemagglutinins, hydrogen cyanide,  raffinose and stachyose  composition  of African  yam  bean (AYB) flour.

The gruels made from AYB flours would be a form of dietary diversification,  which  will enhance AYB food use and contribute to ensuring food security and sustainability in Nigeria. It may also stimulate local production and create employment for rural population.   The study would serve as baseline information for researchers in this area.

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