Enrichment of food blends with bambara groundnut flour: Past, present, and future trends

The aim of this paper was to review the literature (1993 to 2019) on the protein content and use of bambara groundnut in processed foods to improve nutritional value. Bambara groundnut is a legume, which is rich in protein. The protein content of bambara groundnut may vary with cultivar, growing conditions, and location as well as processing method. Complementary foods have been formulated with bambara groundnut as an ingredient. Bambara groundnut has also been used in many other food formulations and this has improved the protein content of such foods. Most of the food products containing high quantity of bambara groundnut despite the high protein content are not acceptable based on sensory evaluation especially taste and flavour. Some researchers have attempted to improve on the sensory properties of products containing bambara groundnut through some processing methods such as roasting, germination, and extrusion. Future studies may include improving the sensory properties of products enriched with bambara groundnut as well as investigating the digestibility of the products using in vivo and in vitro methods.


| INTRODUCTION
Bambara groundnut is a leguminous crop of African origin. The plant can grow under extreme drought conditions. Nutritionally, bambara groundnut is considered a complete food because of its reasonably high protein content (9.60-40.0%; Ogundele, Minnaar, & Emmambux, 2017;Oyeyinka, Umaru, Olatunde, & Joseph, 2019;Uvere, Uwaegbute, & Adedeji, 1999;Anhwange & Atoo, 2015;Okudu & Ojinnaka, 2017;Amarteifio, Tibe, & Njogu, 2010;Laary, Ofori, & Kumaga, 2012;Mohammed, 2014;Nti, 2009) and it has a good balance of the essential amino acids (Yao et al., 2015). Traditionally, the grain has been reportedly used in the production of vegetable milk (Brough, Azam-Ali, & Taylor, 1993;Murevanhema & Jideani, 2013), low fat yoghurt (Falade, Ogundele, Ogunshe, Fayemi, & Ocloo, 2015), value added snacks , and a puree for infant feeding (Oyeyinka, Pillay, & Siwela, 2017). Many researchers claim that bambara groundnut is an underutilized legume (Adzawla et al., 2015;Bonthala et al., 2016;Karunaratne, Walker, & Ruane, 2015;Suhairi, Jahanshiri, & Nizar, 2018). However, it appears that this assertion is no longer valid, because there is recent advancement in the use of the grain in various applications. Furthermore, the bambara groundnut seems to have attained a better status because there are evidences in the literature where the crop has been used to enrich a variety of foods or has been reported to have the potentials for enriching foods. For instance, recent studies reported that bambara groundnut protein hydrolysate and peptide fractions may be potentially used as ingredients in the formulation of functional foods and nutraceuticals against high blood pressure and oxidative stress (Arise, Nwachukwu, Aluko, & Amonsou, 2017). Bambara groundnut has been reportedly used in complementary feeding. Uvere, Onyekwere, and Ngoddy (2010) and Attaugwu, Nwadi, and Uvere (2016) produced cereal-legume-based (maize and bambara groundnut) complementary food, whereas Hayes, Zulu, Mulenga, and Kaputo (2017) compared the acceptability of complementary foods formulated with locally available ingredients. It was reported that mothers/guardians of children 5 to 30 months old evaluated the product and the product with bambara groundnut as the chief ingredient was highly acceptable. It was reported that this choice could be as a result of commodity cost and mother education suggesting that bambara groundnut could solve protein needs of children. In addition, bambara groundnut represent a good source of insoluble dietary fibre. Diedericks and Jideani (2015) produced acceptable white bread enriched with insoluble dietary fibre, which was isolated from bambara groundnut. Bambara groundnut has also been reportedly used in enriching staples such as maize gruel called ogi. Ogi is a very common food; it is a cereal-based food mostly made from maize and consumed by both children and adults.
Some researchers have attempted to increase the nutritional value of ogi with bambara groundnut and have recorded success. Afolabi, Arotupin, Ojo, and Olowokere (2018) fortified ogi from maize, millet, or sorghum with bambara groundnut flour (bambara groundnut [40%] and maize, millet, or sorghum [60%]) and reported 100% nutrient improvement in the protein content of the ogi. The unfortified maize ogi (2.57%) contained a lesser amount of protein compared with the fortified ogi (6.70%). It was reported that the ogi produced from maize and bambara groundnut was the most preferred.
Bambara groundnut has been used in the production of many food products such as milk, yogurt, bread, biscuits, doughnuts, meat analogue, fura, fufu, pasta, and many extruded foods. The aim of this paper was to review the literature on the protein content and use of bambara groundnut in processed foods to improve nutritional value.

| Proximate composition
The proximate composition of bambara grains has been found to vary with cultivar and growing locations (Table 1). In general, protein (9.60-40.0%) and carbohydrate (42.0-70.0%) represent the major components of bambara groundnut, whereas ash (2.90-5.37%), fibre (3.41-6.85%), and fat (4.30-7.24%) contents are relatively low. The low fat contents of pulses such as bambara groundnut is expected because it is generally low in fat when compared with oil seeds such as soybean and peanuts . Although inherent differences in grains may affect proximate composition, growing conditions may affect the composition of bambara groundnut. For instance, some authors found that five different bambara groundnut genotypes grown under the same conditions showed similarity in their composition

| FOOD ENRICHMENT AND FORTIFICATION
Food enrichment involves the addition of micronutrients to a food product, which were lost during processing, whereas fortification involves additional micronutrients not present (or present in small amounts) prior to processing. For the purpose of this review, both terms will be used interchangeably, because literatures that were reviewed sometimes used enrichment whereas others used fortification. According to , fortification can lead to rapid improvements in the micronutrient status of a population at a reasonable cost, and the foods to be fortified must be  production. The control kissra (13.37 g/100 g) had lower protein content compared with the fortified kissra with the different levels F I G U R E 1 Paste and snacks prepared from bambara groundnut and cowpea . (a) Paste prepared from bambara groundnut flour, (b) snack prepared from bambara groundnut flour, (c) paste prepared from bambara groundnut seed, (d) snack prepared from bambara groundnut seed, (e) paste prepared from cowpea flour, (f) snack prepared from cowpea flour, (g) paste prepared from cowpea seed, and (h) snack prepared from cowpea seed (17.93%, 19.38%, and 20.23%, respectively) of bambara groundnut flour fortification, which could be associated with the high protein content (24.53 g/100 g) of the bambara groundnut flour used for the fortification. This result is in agreement with Erukainure et al. (2016), who found significant improvement in the protein content of bread fortified with bambara groundnut. According to these authors, bread fortified with 15% of bambara groundnut flour inclusion was the most acceptable. Yusufu and Ejeh (2018)  and reported that increase in quantity of bambara groundnut flour resulted in increase in protein content.

| Use of bambara groundnut in enriching traditional foods
Traditional foods are highly relished by rural dwellers as well as people living in urban areas especially when the food is prepared under hygienic conditions. These foods have become part of the diet of many, and efforts have been made to improve their nutritional value either through fermentation or the addition of protein-rich grain such as bambara groundnut. For example, fura (millet flour-based food) was fortified with bambara groundnut (Figure 2), and the fortified product showed adequate quantities of essential amino acids with higher lysine content compared with the control sample (Filli, Nkama, & Jideani, 2013). Some authors reported marginal increase (~8%) in protein content for fura fortified with 30% bambara groundnut (Adebayo-Oyetoro, Shotunde, Adeyeye Samuel, & Ogundipe, 2017).
The protein content increased with the increase in the quantity of bambara groundnut flour. However, based on sensory evaluation, the sample with 10% substitution of bambara groundnut was the most preferred.
Adedokun, Onyeneke, Nwokeke, and Obiloma (2017)  reported acceptable sensory properties (colour, taste, flavour, texture, and crispness) of the product. The protein content ranged between 5.30% and 7.51%. The product was also suitable for diabetic patients.

| Use of bambara groundnut in enriching cereal and tuber flours as composites
Awolu (2018)

| Use of bambara groundnut in milk and yogurt production
Due to the growing concern of lactose intolerance, efforts have been geared towards developing alternative milk for the lactose intolerant.
Examples of such milk include milk from plant or vegetable sources such as those extracted from soybean or bambara groundnut. Hardy and Jideani (2017) reported that bambara groundnut has prospects in improving food security through shelf-stable food products, which could be produced from it. They produced protein-rich bambara groundnut milk powder from bambara groundnut flour and water through spray drying of bambara groundnut milk. In this form, the bambara groundnut milk powder, which is rich in protein, may be used to enrich other foods with low protein content. Yogurt has been produced from bambara groundnut milk by some researchers. Pahane, Tatsadjieu, Bernard, and Njintang (2017) produced bambara groundnut milk through aqueous flour extraction by dehulling and parboiling.
An increase in protein content was reported (19.7-25.47%) and on the production of yogurt, a further increase in protein content (1.8-2.6%) was reported. It was concluded that bambara groundnut was a protein-rich legume whose protein content could be enhanced through processing into yogurt. Murevanhema and Jideani (2013) reported that milk from bambara groundnut was more acceptable compared with milk from cowpea and soybean and can sustain the growth of probiotics. It was further reported that with its high nutritional profile, bambara groundnut milk could be fermented with lactic acid bacteria, which can boost therapeutic properties and also address malnutrition.
The addition of bambara groundnut improved the protein content (Table 2) of these food products, but on the other hand, the sensory F I G U R E 3 Acha-based biscuit (80:10:10 acha, bambara nut, and unripeplantain flours) in polyethylene bag and paperboard (Agu et al., 2014) T A B L E 2 Different products enriched or fortified with bambara groundnut

Product name Bambara groundnut (%) Increase in protein (%) Reference
Akpekpa ( properties especially taste and flavour were not acceptable.
Processing methods that can improve these sensory properties needs to be adopted so as to increase sensory acceptability. With the exception of milk and yogurt from bambara groundnut, processing methods such as roasting, germination, and extrusion cooking can be used to address these problems. Some researchers have attempted to produce extruded snacks with bambara groundnut as an ingredient.

| SUMMARY AND FUTURE RESEARCH
Bambara groundnut is a legume rich in protein that has been used to enrich different food products such as snacks and pastries, breakfast cereal and pasta, traditional foods, cereal, and tuber flours as composites. These portray bambara groundnut as an important legume. More research needs to be carried out on bambara groundnut to explore all the inherent potentials of the legume. Furthermore, researches on the utilization of the grain should go beyond adding it to foods to enrich the nutritional value. Future studies may be required to understand the in vitro digestibility of the enriched foods as well using state of the art facilities to analyse the foods.