INTRODUCTION Sorghum ( Sorghum bicolor) originated in Africa, and it adapts uniquely to Africa’s climate, being that it is drought resistant and also able to withstand periods of water-logging (Kimber, 2000). It is one of the most important cereal crops in the semi-arid tropics (SAT). Nigeria has been recorded as the largest producer of sorghum in West Africa, accounting for about 71% of the total regional sorghum output and production of sorghum in Nigeria made up 35% of sorghum produce in Africa (Al-Rabadi et al.
, 2011).However, about 90% of sorghum produced in the United States and India is used for animal feed and not for food, for this reason Nigeria has been ranked as the world’s leading country in the utilization of sorghum as food grain (Catherine et.al., 2013).
Also, it accounts for 50% of the cereal cropland area in West Africa and also as a food security crop known to survive adverse cultivating conditions ( Dicko et al., 2006), nevertheless, sorghum will be elusive without continuous and significant improvement, not only in the production of sorghum but also in its uses as well Though Sorghum is one of the underutilized crop species it plays an important role in the food security, income generation and food culture of the rural dwellers. It is the primary food crop in the northern part of Nigeria even though much attention has not been given to the traditional varieties of sorghum grown by the local farmers and their implicit value has been under-exploited even more-so underestimated. Even though sorghum has been identified with these enormous benefits, nevertheless it has been disregarded since it is perceived as food for the poor (Engle and Altoveros, 2000).Legumes are promising in terms of nutrition, providing food security, agricultural development and in crop rotation in developing countries(Sridhar and Bhat 2007). Significant efforts been geared towards making legumes alternative to expensive feed and also animal protein, especially in developing countries such as Nigeria.
Also research are being carried out on a wide variety of legumes, especially on those which are presently of limited relevance in human nutrition (Okomoda et al., 2016). Hence, the nutritional value of legumes is gaining massive interest globally because of the increasing demand of healthy diets, while the utilization of legumes as protein source in the production of various formulated foods builds up on a daily basis because legumes contains about 17-25% of protein. However even with the nutritive value of legumes, it is masked by incidents of anti-nutritional factors (ANFs), such as trypsin inhibitors, haemagglutinin, and saponin which limits the bioavailability of its nutrients. (Francis et al., 2001).
Cowpea (Vigna unguiculata L.) is an important source of plant protein in human diet. It a legume common to Africa. Cowpea provides a significant amount of dietary protein (18-35%) and lysine. Also in areas where protein rich food are in shortage it is known to provide nutritive value to humans (Khalid et.
al.,2012). Cowpea-based food products can be produced into flour for use in products such as weaning food, infant formula, supplementary diet or diet for the convalescence or even into extruded products which offer convenience and variety of products such as snacks or breakfast cereal .Bambara groundnut (Vigna subterranea) is extensively cultivated in Nigeria, yet it is still considered one of the underutilized legume in Nigeria.
It is nutritionally superior to many legumes and is the preferred crop for many local people (Linnemann, 1990; Brough and Azam-Ali, 1992). Bambara is a rich source of protein (20-25%) which contains about 60% carbohydrate, its protein content is reported to be higher in the essential amino acid methionine than other grain legumes (Stephens, 2003). More so, significance has been placed on the nutritional and economic importance of Bambara groundnut (Mkandawire, 2007). However, despite its high and balanced protein content, Bambara has remained tunder-utilised because of the monotony involved in cooking , contains anti-nutritional factors such as tannins and trypsin inhibitors, and it has poor milling characteristics, because it does not de-hull easily (Barimalaa and Anoghalu, 1997). Never the less, Bambara has high nutrient value and in view of this it has potentials in the development of more acceptable shelf stable food products such as extruded snacks.
Pigeon pea( Cajanus cajan) is cultivated in semi-arid and semi humid tropics. Cajanus cajan is regarded as an important food for food security in regions with low or unreliable rainfall and droughts, since it is drought resistant (Crop Trust, 2014). The seeds of pigeon pea could be brown, red, black or green in colour ,and they are most often hard coated ( Bekele-Tessema, 2007). Pigeonpea is rich in starch, protein, calcium, manganese, crude fiber, fat, trace elements, and minerals.
Besides its high nutritional value, pigeonpea is also used as traditional folk medicine in India, China, Philippines and some other nations. Pigeon peas has been recommended for a balanced diet with cereals and also to supplement for proteins in the rural and poor sector of developing countries (Saxena et.al., 2010) .
However, various factors militate against the somewhat limited utilization of pigeon pea, some of which are the hardness of the seed and also the drudgery process involved in cooking the seeds.( About 8-12 hours of cooking is required for cooking before it becomes soft). However de-hulling the seeds reduce the cooking time (Fasoyiro et al.,2006), while milling these seeds into flour provides a less tedious and well appreciated method of processing pigeon pea. Extrusion technology has shown various advantages over traditional/conventional methods, as it is one of the most efficient processes currently used for resolving world’s hunger and nutritional challenges (Hauck, 1981).
Extruders permit various production application as well as the production of many food products of nutritional importance. More so, the ability of extruders to blend different ingredients in Novel food products has been used in the development of functional foods. The traditional snacks or breakfast cereals can be enhanced by the addition of extra fibre or whole grain flour and even pre-mixes as ingredients during extrusion, thus transforming raw materials into palatable cereal-based products that promote advantageous physiological effects. In addition, functional ingredients that provide high antioxidant and bioactive compounds can be incorporated during the extrusion process to produce products with phytochemicals and other healthy food components, and also increasing their shelf-life.
PROBLEM STATEMENTConsumption of a healthy breakfast ensures that the consumer gets adequate energy needed to go through a successful day. Sorghum is an important cereal grain food, grown globally and rich in nutrients, dietary fibre, and bioactive components yet, it is considered an underutilized cereal and a less-value nutritional source to humans and often used as an animal feed. As the socioeconomic status of population grows daily, preferred cereals like wheat and rice are readily available, affordable, and in abundance thus decreasing the consumption of sorghum (Sheorain et al.
, 2000). One of the reasons for the underutilization of sorghum as human food have been the prevalent ‘misconceptions’ especially in countries that use it as fodder and also the easy availability and acceptability (or palatability) of sorghum-based products. Protein-energy deficiency has been of concern and has been identified as the most ubiquitous form of malnutrition in regions where a great percentage of the population depends on starch-based diets. In view of this, legumes are daily explored for their nutritional advantages and supplementary benefits to cereal based products.
Extruded breakfast cereals which are produced from starch based products require fortification with macro and micro nutrient-rich legumes, thus placing emphasis on underutilized legumes with desirable nutritional profile is of importanceJUSTIFICATION OF STUDYCereal has been a significant source of food across the globe and further awareness of the utilization of sorghum will definitely lead to increase in its demand and production. Moreover, sorghum grains has potentials in its use as food products because it is a less expensive substitute to other cereal ingredients such as corn and rice. Also, optimum mix proportion of legumes and cereals, and the processing characteristics of extrusion will provide products with bioavailable amino acid profile as well as palatable products.Furthermore, fortification of sorghum with legumes will further diversify and improve the utilization of sorghum. This fortification is to compensate for the lacking nutrients and more-so supplement for the micro and macro nutrient lacking in cereals, while also focusing on processing methods like extrusion technology which is efficient in the elimination or reduction of anti nutritional factors such as phytic acid, tannin etc, which is prevalent in cereal and legume .In other to meet consumers’ requirements, which presently is fixated on nutrition and consumption of healthy foods which will promote the healthy and positive life style, extrusion technology has been found a useful tool that yields greater efficiency and higher productivity, increased output, ,consequently facilitating the production of numerous snacks and improving the final product qualityMoreover, extrusion technique is gaining prominence in the production of convenient foods and snacks, and research has shown that extrusion is a viable tool for enhancing protein digestibility which involves using controlled conditions of heat and moisture which lowers the formation of disulphide bonds in proteins.
(Mahasukhnothachat et al., 2010)OBJECTIVESThe general objective of this research was to optimize the blends of sorghum with Bambara, cowpea and guinea pea, and to optimize the effect of the different legumes, extrusion parameters on quality attributes as well as the in-vitro digestibility of extruded products from sorghum and Bambara, cowpea and pigeon pea.Specific objectives;Optimize the formulation ratio of sorghum and Bambara, cowpea and guinea pea composite flour using the mixture design methodology.Characterize the different blends and formulation levels for their proximate composition and anti nutritional factor.Optimize the effect of process parameters; feed moisture, barrel temperature, screw speed , extrusion type on the chemical, physical, functional, textural properties of the extruded product.Assess the effect of extrusion process and parameters on the in-vitro starch and protein digestibility of the extruded productsAssess the effect of the process parameters on the sensory properties of the extruded products.
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