The effects of fermentation and toasting on the nutrients and antinutrients composition of Senna obtusifoliai seeds were investigated. Senna obtusifolia seeds were fermented with Aspergillus niger at an ambient (27-30°C) temperature for five days. Senna obtusifolia seeds were also toasted at 80oC in open pan using hot plate for 10 min. Raw Senna obtusifolia seeds contained 7.45mg/100g moisture, 33.33mg/100g crude protein, 17.25mg/100g lipid, 9.49mg/100g dietary fibre, 4.50mg/100g ash, 37.99mg/100g nitrogen free extract. Antinutrients composition of raw Senna obtusifolia was 3.95mg/100g tannins, 3.74mg/100g phytates, 2.13mg/100g oxalates and 2.62mg/100g saponins, 11.23 TUI/mg trypsin inhibitor and 5.77 IC50 (mg/ml) alpha amylase inhibitor. Fermentation increased the crude protein of Senna obtusifolia but reduced nitrogen free extract, moisture, lipid and dietary fibre. Toasting reduced moisture, dietary fibre, crude protein but increased lipid, ash and nitrogen free extract. Toasting/fermentation (toasting followed with fermentation) increased moisture, nitrogen free extract and ash but reduced crude protein, dietary fibre and lipid. Fermentation reduced the tannins by 38%, phytates by 84%, oxalates by 36%, saponins by 37%, trypsin inhibitor by 12% and α-amylase inhibitor to 6.40 IC50 (mg/ml) while toasting reduced tannins by 63%, phytates by 89%, oxalates by 61%, saponins by 66%, trypsin inhibitor by 40% and α-amylase inhibitor to 13.05 IC50 (mg/ml). Toasting/fermentation reduced tannins by 70%, phytates by 93%, oxalates by 54%, saponins by 91%, trypsin inhibitor by 43% and α-amylase inbitor to 19.54 IC50 (mg/ml). The in vitro protein digestibility of raw Senna obtusifolia was 7.80%. The reduction in antinutritional factors was concomitant with a significant (P ≤ 0.05) increase in protein digestibility after processing of the samples, fermentation, toasting and toasting/fermentation increased the in vitro protein digestibility of Senna obtusifolia to 45%, 22%, and 25%, respectively. Raw Senna obtusifolia seeds contained both essential and non essential amino acids with fermentation and toasting increasing the amino acids content respectively but toasting/fermentation slightly reduced the amino acid content. The total minerals contents Senna obtusifolia seeds (Ca, Zn, K, Na, Fe and Mg) were reduced after processing. Fermentation reduced all the total mineral contents, toasting increased Fe, Mg, K and Na but reduced Ca and Zn. Toasting/fermentation reduced Ca, Mg, Zn, K and Na but increased Fe. Results obtained indicated that fermentation had significant influence on the proximate composition, in vitro protein digestibility, antinutritional factors, amino acids and mineral contents of Senna obtusifolia seeds.

Food-based approaches such as dietary diversification, fortification and biofortification are necessary strategies to prevent the debilitating effects of malnutrition by promoting the consumption of foods that are naturally rich in micronutrients. Dietary diversification has been advocated internationally for the improvement of micronutrient intake and status (Hedwig et al., 2012). An increase in meat and animal products consumption is eminent in emerging and developing economies (Delgado et al., 1999), yet the consumption of animal protein is still low in developing countries like Nigeria (Okojie, 1999; FAO, 2001). One reason often advanced for this scenario is the high cost of animal proteins often beyond the purchasing power of the majority and poor people of these countries. In order to boost the animal protein consumption of developing countries and achieve Millennium Developmoent Goal 1 (MDG 1), there is need to reduce the cost of livestock products by bringing down the cost of their feed. Soybean which is the main source of plant protein in the diets of farm animals is increasingly finding new uses as biodiesel stock in response to the deepening world energy crisis (Sasson, 2012). In addition, the use of soybean for food and energy by man often takes precedence over its use for livestock feeding. This dilemma has encouraged livestock nutritionists and feed millers to seek for alternatives to soybean as plant protein source in livestock diets. The alternative protein source has to be cheap, locally available and preferably not used as food by man. Dietary diversification reflects household access to varieties of foods and can also act as a proxy for individuals’ nutrient adequacy. Wild plants play an important role in the diet of most rural dwellers in Nigeria. These plants tend to be drought tolerant and are gathered both in times of plenty as well as times of need. Throughout the year, the plants play an important role in supplying nutrients and calories especially during the dry season when cultivated vegetables are scarce (Freiberger et al., 1998). Although commonly eaten in the rural areas they are also consumed by urban people who buy from traders who also collect them from the wild.

The use of toxic plants as food after fermentation or heat treatment is known in Africa and other parts of the world (Ganiyu, 2005). Antinutritional factors such as enzyme inhibitors, hemagglutinin, flatulence factors, polyphenols, tannins and phytic acid inhibit the proteolytic activity of the digestive enzymes such as pepsin and trypsin as well as the availability of minerals (Deshpande and Cheryan, 1983). Minerals from plant sources, particularly those from plant seeds are less bioaccessible than those from animal’s sources due in part to phytic acid, tannins and fiber content (Moelijopawiro et al., 1998). These antinutritional factors chelate dietary minerals in the gastrointestinal tract reducing bioaccessibility and bioavailability (Frolich, 1995). Polyphenols can form complexes with metal cations through carboxylic and hydroxylic groups and thus interfere with the intestinal absorption of essential minerals such as calcium (Valencia et al., 1999). Phytic acid is naturally occurring as a hexaphosphate derivative of inositol found in plants and in almost all mammalian cells. It consists of six phosphate moieties and chelates metal irons such as Ca, Mg, Zn, Mn, Cu and Fe to form insoluble complexes that are not readily absorbed (Graf and Eaton, 1993). Tannins also complex with enzymes of the digestive tract adversely affecting utilization of proteins and carbohydrates and resulting in reduced growth, feeding efficiency, metabolizable energy and bioavailability of amino acids (Onyango et al., 2005). Several treatments have been applied to remove or reduce the amount of antinutrient from plant. Few examples among them are: fermentation, germination, thermal treatments (cooking) and soaking procedures (Abd El-Hady and Habiba, 2003; Martin-Cabrejas et al., 2004). In general, these processing methods enhance the nutritive value, reduce the amount of undesirable compounds and improve the protein digestibility of legumes (Martin- Cabrejas et al., 2004). Sicklepod is rich in Ca, Mg and P as major minerals while Fe, Zn and Mn were present at lower levels (Ousman et al., 2005).

The plant Senna obtusifolia belongs to the kingdom plantae, family fabaceae, a common annual plant that grows wild in Northern Nigeria. The plant is considered a serious weed to Agriculturists in many places. It grows on well-drained fertile soil. Similarly, it is suited for cleared coastal forest countries. Senna obtusifolia has been regarded as indigenous leafy vegetable of the Sahel with potential of providing vegetable to the rural population in the month of August and September (Pasternak et al., 2006). The young tender of Senna obtusifolia occasionally used as vegetable throughout Africa and elsewhere and the plant is cultivated in homes for this purpose in several countries including Senegal, Ghana, Cameroon, and Ethiopia. If eaten frequently or in large quantities could cause diarrhea (Irwin and Barneby, 1982). In Nigeria the seeds and roots of Senna obtusifolia of no doubt have some laxatives effects. It is used as decoction febrifuge and for the treatment of scorpion stings, gingivitis, dysentery and diarrhea (David, 2002; Fowler, 2006). As the seeds are reputedly poisonous (Crowhurst et al., 1972), therefore processing is necessary before eating. The cooked vegetable tastes bitter but has an attractive consistency. Senna obtusifolia will probably remain a minor vegetable.

1.1.      Statement of Research Problem
Soaring food prices have triggered an increase in hunger worldwide, especially in sub-Saharan African countries like Nigeria. The increase in prices of food has been attributed to several factors that include production shortfalls due to drought and floods; impact of climate change; increased demand for biofuel; emerging consumption habits of fast growing economics of some nations as well as trade policies to stabilize the food market crisis (FAO, 2008). According to the W. H. O. (2013), malnutrition is one of the leading causes of death globally. It is well established that majority of people in developing countries depend mainly on cereal grains as their staple food due to limited income and high prices of animal foods (Sokrab et al., 2012). Senna obtusifolia has some limitations due to the presence of antinutritional factors, such as trypsin and amylase inhibitors, phytate and tannins. These compounds are known to interfere with protein and carbohydrate digestion and mineral bioavailability. Reduction or elimination of these undesirable components is essential for improving the nutritional quality of Senna obtusifolia and effectively utilizing their full potential as human food. Efforts however, are directed at improving the nutritional value of Senna obtusifolia seeds. Various simple processing methods such as soaking, sprouting, cooking and fermentation have been found to improve the nutritional value of plant (Yagoub and Abdalla, 2007; Mohamed Nour et al., 2010). It is well known that fermentation decreased the values of antinutritional factors as well as increased the in vitro protein and starch digestibilities and thus improve the nutritional quality of plant (Elkhalifa et al., 2004; Idris et al., 2005; Abdelseed et al., 2011; Mohammed et al., 2011). Cooking on the other hand has been reported to reduce the in vitro protein digestibility, whereas combining fermentation with cooking had significantly improved protein digestibility over wet cooking alone (Taylor and Taylor, 2002).

Since the seeds of Senna obtusifolia contain antinutritional factors that can be harmful to human, this calls for the adoption of effective processing methods like boiling, soaking, roasting, fermentation and sprouting before inclusion in diets. It is also important to use the seeds in a feeding trial with the aim of evaluating their biological values to humans.

1.2.     Justification
Presence of antinutritional factors in this plant is one of the factors limiting its use in food formulation (Oladele and Aina, 2007). However, there is few detailed information on the nutritional profile of the seeds in relation to human consumption within the guinea savanna environment of Nigeria, where this plant is prevalent. This is very important since the nutritional and chemical value of this plant is partly influenced by geographical location which is shaped by factors like soil and climatic conditions (FAO, 2004). Therefore to gather reliable information regarding the use of this plant as food, the chemical and nutritional characteristics of this food needs to be carefully assessed in order to prevent errors in predicting human health and environmental effects impairing the survival of mankind.

Also most developing tropical countries have depended upon soybeans and other common legume grains as protein source for both humans and animals (Vadivel et al., 2008) but, their production is not sufficient to meet the protein requirements of the increasing population and expanding livestock industries (Vijayakumari et al., 2007). The competition between human and livestock for the consumption of soybean and the increasing role of soybean in the world as biodiesel feedstock (Cotula et al., 2008) have increased its cost and demand and heightened the competition between human and animal for soybeans. Consequently, the search for a novel, high quality, cheap and readily available source of plant protein to replace soybean (Adeniji et al., 2005; Obun and Ayanwale, 2006). One of such legumes with great prospect as alternative and replacement for soybean is Senna obtusifolia (sickle pod).

1.3.      Null Hypothesis
Toasting and fermentation have no effect on the nutritive value of (Senna obtusifolia) sickle pod seeds

1.4.      Aim
The aim of this research is to propose an effective processing method for safe utilization of sickle pod seeds.

1.5.       Specific Objectives
      To determine the effect of processing (toasting, fermentation and toasting + fermentation) on the proximate composition of Senna obtusifolia seeds.

      To determine the effect of processing (toasting, fermentation and toasting + fermentation) on the antinutritional factors content of Senna obtusifolia seeds.

      To determine the effect of processing (toasting, fermentation and toasting + fermentation) on the in vitro protein digestibility of seeds of Senna obtusifolia.

      To determine the effect of processing (toasting, fermentation and toasting + fermentation) on the amino acid profile of the of Senna obtusifolia seeds.

      To determine the effect of processing (toasting, fermentation and toasting + fermentation) on the mineral composition of Senna obtusifolia seeds.

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