PROXIMATE AND SENSORY CHARACTERISTICS OF “AKARA” PRODUCED FROM DIFFERENT BLENDS OF AFRICAN YAM BEAN AND COWPEA

ABSTRACT

Low nutritional value and inconsistent sensory qualities arising from crude and nonstandard processing operations characterise most Nigerian cowpea-based snacks including akara. African Yam Bean Seed (AYB) is an underutilised crop with high nutritional value, but literature is sparse on its utilisation to enrich cowpea snacks. This study was designed to improve nutritional valueof akara by incorporating AYB Flour (AYBF).

Varieties of cowpea (BR-9928-DMR-SY and TZL-Comp-4C2) and AYB (Tss-9 and Tss-30) were tested for processing suitability using physical and chemical properties. The better quality cowpea and easier to dehull AYB were processed into flours at ratios 100:0, 80:20, 70:30, 60:40 and 0:100. Proximate composition, Trypsin Inhibition Activity (TIA), betacarotene and amylose contents, functional and pasting properties of the flour blends were determined by standard methods. Using Response Surface Methodology (RSM) experimental design, batters produced from blends of cowpea and AYBF at ratios 80:20,

70:30 and 60:40 were deep fried at varied temperatures (150, 160 and 170^oC) and time (8,

10 and 12 min.) according to 17 combinations associated with three independent variables. Processing conditions including frying temperature, frying time and quantity of AYBF in the flour blends were independent variables while products‟ qualities were dependent variables. Proximate composition, TIA and texture of snacks were determined using AOAC methods. Akarawith highest products‟ qualities were obtained from RSM as the optimum processing conditions. Akara was prepared at these optimum conditions and subjected to rancidity test weekly for fourteen weeks to determine its storage life using free fatty acid test. The akaraand casein diet were separately fed to male wistar rats (90-110g) for 28 days using casein diet as standard to determine its protein availability. Sensory attributes of the products were determined using semi-trained panelists. Data were analysed using ANOVA at p=0.05.

The BR-9928-DMR-SY cowpea was selected for its higher nutrient density (beta-carotene,

1.8µg/g). The AYB (Tss-30) was chosen based on its better ease of dehulling. Crude protein (10.5-15.7%), total ash (1.5-2.2%), crude fibre (1.3-4.1%), sugar (4.1-5.3%), TIA (2.9-6.7%) increased, while crude fat (4.9-3.9%), starch (66.6-51.2%), amylose (26.5-24.8%) and betacarotene (1.8-0.9µg/g) decreased with increase in AYBF in the flour blends. Functional parameters showed no significant change among the flour blends except oil absorption capacity (80.1-57.1%). Peak viscosity (479-580cp) increased but pasting temperature (89.882.1^oC) decreased with increase in AYBF. While crude protein content was not adversely affected with higher frying temperature and time, TIA (6.7-2.9%) decreased significantly, but crude fibre, crude fat, sugar and starch contents increased. Texture increased with increase in frying time. The best product was obtained from blend of Cowpea-AYB at ratio 70:30, fried at temperature, 155^oC and time, 11.5min. Level of rancidity of the snack was tolerable up to 12 weeks. Protein availability of the akarawas not significantly different (p<0.05) from that of casein. The akaraproduced was acceptable to panelists up to 10 weeks of storage.

Addition of African yam bean seed flour to akaraimproved its nutritional content, creating a novel use for African yam bean seed. Standard processing conditions for producing akaraof consistent sensory qualities was established.

Keywords: African yam bean seed flour, Cowpea flour, Akara, Nutritional quality.

CHAPTER ONE

1. INTRODUCTION

1.1       Background of the study

Some traditional food products in Nigeria are characterised by low nutritional value, variable sensory quality and short shelf life. The poor packaging and storage techniques make them prone to pest and rodent attack and susceptible to microbial spoilage (Aiyeleye and Eleyinmi, 1997). According to Sobukola et al. (2009), the technologies employed in the processing, distribution and storage of indigenous snack foods are based on the traditional knowledge. Therefore, there is need for upgrading these technologies as a way of improving nutritional, sensory and storage properties of these products. Most often snacks do not provide nutrients in adequate quantities needed by the body (Omueti and Morton, 1996); this may be due to their composition or the production process. Thus, it is necessary to ensure that every food consumed by an individual contains required nutrients in adequate amounts. This is especially important due to the fact that many people now work outside their homes and are becoming more dependent on snacks for the supply of part of their daily food requirements.

According to Tetteweiler (1991), a snack is a small meal in the broadest sense “and snacking is the consumption of easy- to- handle food products in either solid or liquid form, with little or no preparation. It is eaten in small amount usually between main meals or instead of a meal. A snack is commonly used as convenience food. The need for convenience food is borne out of the need to spend less valuable time and energy in the kitchen preparing meals (Idowu et al., 2010). Snacking is on the increase worldwide and this results primarily from factors such as increase in one person households, a higher proportion of working mothers and more school aged children obtaining their own meals and refreshments.

It would therefore be worthwhile if an acceptable snack with high nutritional quality that could be useful in nutritional programmes to combat malnutrition and nutrient deficiencies could be developed (Rosa et al., 2003). In the tropics, cowpea is a common cereal crop, of good source of carbohydrate, vitamin and minerals that can be processed into a wide range of food items and snacks. Cowpea grains are abundant, stable crop in Nigeria with different varieties.  Nutritional contents of the cowpea varies from one variety to another, while some cowpeavarieties contain β-carotene, other do not. Punita (2006) investigated the nutritional composition of three cowpea varieties and attributed the differences in chemical composition to their genetic composition, environmental factors and agronomic practices. Therefore, appropriate variety of cowpea can be chosen in production of snacks to attain increased nutritional contents. Some of the cowpea-based local snacks include; aadun (cowpea snack), akara (corn cake) and donkwa (cowpea-peanut ball). Although, these snacks and appetizers are popular food items, with a long history of consumption especially among the low income populace, there exists a paucity of information on their nutritive and functional attributes (Aletor and Ojelabi, 2007). Like most cereal-based foods, akara is rich in carbohydrate, but low in protein and deficient in some essential amino acids, particularly lysine (Uzo-Peters et al., 2008, Ihekoronye and Ngoddy, 1985). This makes the product nutritionally deficient thus necessitating its enrichment. Improving these snacks therefore will involve the understanding of the production processes and optimisation of these production processes. It will also involve inclusion of nutrient-dense materials such as African yam bean and storage studies to know the appropriate storage conditions for the product.

Since these cowpea-based snacks particularly akara are commonly consumed among adults and children especially the school-aged children as refreshment in South-Western Nigeria, it becomes necessary to improve its protein and micronutrients contents. Vitamin A deficiency (VAD) has been reported as a severe public health problem as 29.5% of children (<5years) are vitamin A deficient with serum retinol<0.70µm\L (Maziya-Dixon et al., 2006). Recommended Dietary Allowance (RDA) of vitamin A for children is 300-600µg (1200IU2400IU) and 800-1000 µg in adults (Smolin and Grosvenor, 2003). Vitamin A activity in food is mainly due to all trans-isomer of retinol, which is the most abundant and biologically active member of the vitamin A group. In diet, β-carotene and other carotenoids provide most of the vitamin A. The labeling of food regulations require that vitamin A is calculated as micrograms of retinol or retinol equivalent on the basis that 6µg of β-carotene equals 1µg of retinol equivalent. Therefore 6µg of beta-carotene is equivalent to 1 µg of vitamin A (Smolin and Grosvenor, 2003, Pearson, 1976). Food materials or commodities high in β-carotene such as yellow cowpea, sorghum could be used in akaraproduction to enhance its vitamin A content.

Legume crops such as soybean, cowpea, groundnut, African yam bean, have very high protein content. It is well documented that most leguminous plant seeds are rich in nutrients such as digestible protein with a good array of amino acids and minerals (Fagbemi et al., 2004; Agbede and Aletor, 2003).

African Yam Bean (AYB) (Sphenostylisstenocarpa)  is one of the less utilised legumes that are gradually going into extinction (Klu et al., 2001); this may be due to the long cooking time it requires and its taste. However, it can be used in preparation of other food products. According to Adewale et al., (2010), the vast genetic and economic potentials of AYB have been recognized; especially in reducing malnutrition among Africans and the crop has not received adequate research attention. Up till now, it is classified as a neglected underutilised species (NUS) (Bioversity, 2009).  Its intended use in improving nutritional quality of cowpea-based snacks will add value to these cowpea-based snacks as well as provide more utilisation for the legume.

Although plant proteins are considered inferior to animal proteins, the former are becoming the choice of the populace due to absence of cholesterol and other components of animal protein that pose health risks to consumers.  Apart from the use of soybean as an alternative to animal protein, protein from other plant sources should be exploited. Nutritionally, AYB competes with cowpea and soybeans in terms of protein and amino acids contents (NAS, 1979). The protein content in AYBS grains ranged between 21 and 29% and in the tubers, it is about 2 to 3 times the amount in potatoes (Uguru and Madukaife, 2001, Okigbo, 1973). During nutritional evaluation of 44 genotypes of AYB, the crop was reported to be well balanced in essential amino acids and has higher amino acid content than pigeon pea, cowpea, and bambara groundnut (Uguru and Madukaife, 2001). Like most legumes, AYB will improve both protein quantity and quality of cowpea, since the methionine-containing cowpea will be complemented by lysine-containing AYB, providing a better balance of amino acids, especially the essential amino acids. Amino acid analyses indicated that the lysine and methionine levels in the protein of AYB are equal to or better than, those of soybeans

(Evans and Boutler, 1974).  FAO/WHO/UNU (1992) recommended dietary intake states that an average man requires 65g of protein and 2500kcal of energy per day while a child between age 4 and 7 requires 20g of protein per day and 1830kcal of energy per day. This nutritional requirement has to be borne in mind while formulating products of improved nutritional qualities.

Frying (for example, akara, kulikuli) and roasting (for example, pop corn, groundnut) are commonly used in processing of traditional snacks. Despite acrylamide scare and other limitations associated with fried products, the market of fried products is still growing. Frying is commonly used to cook food. A fried product tastes good, has a good flavour and is prepared within few minutes. Even though frying is an old process of manufacturing food products worldwide, optimisation of its processing parameters may improve fried products‟ quality. It will have effect on the oil content, texture (crispness), color, and nutritional value of the final product (Lui-ping et al., 2005).

One of the most popular methods used in food product and process optimisation in the last two decades is Response Surface Methodology (RSM). RSM is a collection of statistical and mathematical techniques useful for developing, improving and optimising process in which a response of interest is influenced by several variables and the objective is to optimise the process (Myers and Montgomery, 1995). RSM has important application in the design, development and formulation of new products, as well as in the improvement of existing product design (Bas and Boyaci, 2007).

RSM has been very popular for optimisation studies in recent years in the area of Food Science and Technology. These include the optimisation of roasting temperature and time during oil extraction from orange (Akinoso et al., 2011); development of complementary foods from extruded cowpea (Vigna unguiculata (L) and Acha (Digitaria stapf) blends (Olapade, 2010); optimisation of frying conditions during deep fat frying of yam slices (Sobukola et al., 2008); optimisation of process variables for the preparation of expanded finger millet (Ushakumari et al., 2007) and optimisation of vacuum drying conditions of carrot chips (Lui-ping et al., 2005);.

Use of better quality cowpea, enrichment with African yam bean as well as use of response surface methodology for standardisation of the processing methods and storage studies of the cowpea-based snacks will suggest the appropriate processing and storage conditions. This will result in improved sensory, nutritional and storage properties of this Nigerian cowpeabased snacks (Akara).

1.2 Objectives of the Study

The main objective of this study was to develop and optimise akara from blends of cowpea and AYB to attain improved nutritional value, better storage and consistent sensory qualities. While the specific objectives of this study were to:

1. determine the properties of selected cowpea and African yam bean seeds cultivars for processing suitability,
2. evaluate the effect of some processing parameters (frying temperature, frying time and quantity of AYB flour) on the physico-chemical, functional, nutritional and sensory properties of the flour blends and the cowpea-based snacks.

• determine storage properties and adsorption isotherm characteristics of the products and

1. assess the consumers‟ acceptability of the products developed.

1.3        Justification of study

There is little information on the utilization of African yam bean seed, a nutrient dense but neglected underutilized species (NUS) of legume) to enrich cowpea snacks. The development of these cowpea-based snacks through value-added processes will establish appropriate and optimum conditions for improving the product quality. It will offer wider utilisation to AYB, leading to job creation both at farm and industrial level. Also, the crude, nonstandardised processing operations associated with this Nigerian snack will be upgraded as a way of improving its nutritional, sensory and storage properties. This research work is in line with national policies of food security and upgrading traditional food processing techniques, thus adding value to Nigerian snacks.

PROXIMATE AND SENSORY CHARACTERISTICS OF “AKARA” PRODUCED FROM DIFFERENT BLENDS OF AFRICAN YAM BEAN AND COWPEA