Abstract: The study evaluated the nutritive value of seeds of wild Senna obtusifolia plants as an alternative plant protein source in livestock diets. Proximate composition results showed high dry matter (92.50%), crude protein (29.54%) and crude fiber (10.18%), but low ether extract, nitrogen free extract, ash and calorific values. The vitamin content results showed poor vitamins B2 , B1, C and A but the seeds were rich in vitamin B3 (1.85 mg/100 g) values compared to other seeds. The seeds were also abundant in calcium (960 mg/100 g), potassium (1,200 mg/100 g), phosphorus (810 mg/100 g), sodium (600 mg/100 g), magnesium (640 mg/100 g), iron (234.60 mg/100 g), zinc (53.12 mg/100 g) and copper (10.48 mg/100 g) but low in molybdenum, cobalt, chromium, selenium, sulphur and fluorine. The amino acid profile reveals a high concentration of leucine (7.60 g/100 g protein), histidine (2.11 g/100 g protein), proline (2.33 g/100 g protein) and glycine (4.11 g/100 g protein) while the rest of the amino acids were of low concentration in the raw seed. The concentration of anti-nutrients in the legume seeds recorded high values (260, 185, 388.50 and 83.25 mg/100 g) for alkaloid, saponin, tannin and oxalate respectively, while phytate, hydrocyanic acid and phytohaemaglutinin levels were low. The high level of most anti-nutrients indicates the potential for interfering with the utilization of the nutrients by the animals. This therefore, creates a need for detoxification of the seeds through processing before using in livestock feeds.
INTRODUCTION
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 economies of some nations as well as trade policies to stabilize the food market crises (FAO, 2008). The hike has aggravated the already precariously low animal source food consumption of about 3-5 kg/capita/year in developing countries compared to the world average of 38 kg/capita/year and the USA’s 124 kg/capita/year (Speedy, 2003). In addition, there is the projected 56% growth in the demand for meat by 2020, especially in developing countries (Delgado et al., 1999). This shall likely heighten the demand against a weak supply. The animal protein component of this food demand is more crucial because it is the main determinant of food quality since meat, eggs and milk are an excellent source of high quality protein, containing large amount of minerals and essential B vitamins (Osasanya et al., 2005; Speedy, 2003).
In order to increase the consumption of animal protein in developing countries, it is necessary to reduce the cost of meat, milk and eggs, thereby making them accessible and affordable to the majority of the people. However, feed constitutes 55-80% of the cost of production of livestock products (Carew et al., 1998). Soybean is the main conventional plant protein source for livestock diets in Nigeria. Soybeans also serve as human food. The competition between human and livestock for the consumption of soybean and the increasing role of soybean in the world as a biodiesel feedstock (Cotula et al., 2008) have increased its cost and demand and heightened the competition between human and beast for soybeans. Consequently, the search for a novel, high quality, cheap and readily available source of plant protein to replace soybeans is now a major concern of livestock nutritionists in much of the developing world even more than before (Obun and Ayanwale, 2006; Adeniji et al., 2005). One of such legumes with great prospect as alternative and replacement for soybean is Senna obtusifolia (sickle pod).
Sickle pod is an annual plant considered a serious weed in many places. It is a competitive woody shrub that grows vigorously across the tropics. It grows to a height of about 1.5-2.5 m tall and 1 m wide. The seed pod is 10-15 cm long, 3-5 mm wide, slender and sickle shaped. The plant prefers well drained fertile soils and well suited for cleared coastal forest countries. The leaves, seeds and roots are used for folk medicine especially in Asia. The roasted seeds are used for tea, coffee or food additives. It is also used as a thickener and the seeds are used for commercial cassia gum (Queensland Government, 2006). The plant contains some anti-nutrients, therefore, it is thought of as poisonous to livestock (Ednilson et al., 1998). Also, it is regarded as one of the indigenous leafy vegetable of the Sahel with the potential to provide food to the rural population in August and September when grain reserves from the previous year harvest have been exhausted. The domestication of this legume has begun (Paster et al., 2007).
The proximate composition of leaves and seeds of this plant as reported by Faruq et al. (2002) gave promising results. However, there is dearth of detailed information on the nutritional profile of the seeds, in relation to livestock feeding, within the guinea savanna environment of Nigeria, where this plant is prevalent. This is very important since the nutritional and chemical value of a feedstuff is partly influenced by geographical location which is shaped by factors like soil and climatic conditions of the place (FAO, 2004). Therefore, to gather reliable information regarding the use of a feedstuff as livestock feed, the chemical and nutritional characteristics of that feedstuff need to be carefully assessed in order to prevent errors in predicting animal performance and environmental effects impairing the economics of animal products.
This study was, therefore, designed to evaluate the chemical and nutritional composition of seeds of wild S. obtusifolia plants growing in Obanliku, South Eastern Nigeria in order to generate data for the development of this plant as an alternative plant protein source in the developing countries of the tropics.
MATERIALS AND METHODS
Location of the Study Area and Collection of Seeds
The matured seeds of S. obtusifolia were harvested from wild plants
growing in mountainous guinea savanna region of Obanliku Local Government Area,
Cross River State in South-Eastern Nigeria. Obanliku Local Government Area is
located between Latitude 6°15' and 6°30' North of the Equator and longitude
9°6' and 9°15' East of the Greenwich Meridian. The plants were previously
identified by a plant taxonomist at the Botany Unit, Department of Biological
Sciences of the University of Calabar, Nigeria. The study was carried out at
the Department of Animal Science Laboratory of the University of Calabar, Nigeria
from November, 2008 to March, 2009.
Preparation of the Seeds
The fresh seeds were picked and oven dried at 55°C in a paper envelope
for about 24 h to a constant weight for the calculation of percentage dry matter
(%DM) content (Abuye et al., 2003). The dry seeds
were ground to powder using a laboratory blender and sieved using a 1 mm mesh
sieve. Each analysis was done in triplicates and the mean of the three values
was presented as the result.
Proximate Composition Determination
The sieved powder was used for the analysis of Crude Protein (CP), Crude
Fibre (CF), Ether Extract (EE) and ash while Nitrogen Free Extract (NFE) was
calculated. This was done according to the methods of AOAC (1990).
Estimation of Energy
The calorific value of the seeds was estimated by multiplying CP, EE and
NFE values by 16.7, 37.7 and 16.7, respectively (Siddhuraju
et al., 1992).
Vitamin Analysis
Vitamin C was determined according to the method described by Adebooye
(2008). Ascorbic acid was measured by titration with phenolindo-2, 6-dichlorophenol
(DPIP). The powder (0.2 g) was mixed with 4 m L-1 of a buffer solution
made up of 1 g L-1 oxalic acid and 4 g L-1 sodium acetate
anhydrous. This was titrated against a solution containing 295 mg L-1
DPIP and 100 mg L-1 sodium bicarbonate. The results were expressed
as mg/100 g DM. Vitamin A was determined using the method described by Zhang
and Hamauzu (2004) where 15 g of powdered sample was homogenized with 10
mL acetone at -20°C. The homogenate was filtered with four layers of cheesecloth.
The residue was treated with acetone (-20°C) for three successive extractions
until the green colour could no longer be visually detected in the extract and
residue. The filtrate was combined and centrifuged at 4000 rpm for 10 min. The
supernatant was collected and filtered through a 0.45 μm Advantec filter
pore for HPLC analysis. Samples were separated on a Luna 5 μ C18 column
at 40°C by an HPLC. The mobile phase consisted of acetonitrile: water and
ethyl acetate. The flow rate was 1.0 mL min-1. samples were detected
at 450 nm. The carotenoids were expressed as IU. Vitamin B1, B2, B3 and E were
determined spectrophotometrically as stated by AOAC (1999).
Mineral Elements Analysis
The samples were incinerated at 450°C for 12 h in a muffle furnace and
an acid digest was prepared by oxidizing each sub-sample with a nitric/perchloric
acid (2:1) mixture. Aliquots were used to estimate Na and K by flame photometer
(Flame Photometer Model-EEL) as reported by Zia-Ul-Haq et
al. (2007). All other minerals reported except phosphorus were determined
using a Perkin-Elmer Model 5000 Atomic Absorption Spectro-photometer (AOAC,
1999). Phosphorus content in the triple acid digested extract was determined
by the phosphovanado-molybdate (yellow) method according to the method of AOAC
(1999).
Amino Acid Profile Determination
The amino acid profile of the sample was determined using methods described
by Shahidi et al. (1999). The sample was dried
to constant weight, defatted, hydrolysed, evaporated in a rotary evaporator
and loaded into the Technicon Sequential Multi-sample Amino Acid Analyzer (TSM)
using ion-exchange chromatography (Technicon Isnstruments Corporation, Dublin,
Ireland). Details have been outlined by Adeyeye and Afolabi
(2004).
Antinutritional Factors Determination
Phytates were determined according to the methods described by Muhammad
et al. (1986) using chromatophore reagent. Tannins were analyzed using
the modified Vanidlin-HCl method as described by Zia-ul-Haq
et al. (2007). One gram of test sample was treated with methanol
(28°C, 12 h) with occasional shaking. Decanted methanol was made up to 25
mL and filtered (Whatman No. 1). One milliliter of the extract was treated with
5 mL of the reagent mixture (1:1, 4% vanillin in methanol and 8% concentrated
HCl in methanol). The colour developed was read at 500 nm after 20 min, using
catechin as a standard, with a spectrophotometer. The tannin contents were then
determined from standard curves. Saponins were extracted and estimated according
to the methods of Shukla and Thakur (1986). Estimation
of oxalates was by the procedures described by Tuleun and
Patrick (2007). Hydrocyanic acid was determined according to the method
of Rao and Hahn (1984). Phytohaemagylutinin activity
was estimated as stated by Liener and Hill (1953).
RESULTS
The DM content of the wet seeds was 92.50% while the percentage CP, EE, CF, NFE and ash contents of S. obtusifolia were 29.54, 2.31, 10.18, 46.77 and 3.70% DM, respectively. The calorific value of S. obtusifolia was 325.28 kcal/100 g (Table 1).
Vitamins B2 (riboflavin), B1 (thiamine), B3 (Niacin) and C (Ascorbic acid) values in mg/100 g of sample were 0.10, 0.60, 1.85 and 11.88, respectively, while vitamin A value in IU/100 g sample was 213.60. However, vitamin E (α-tocopherol) was not detected (Table 2).
Alkaloid, saponin, tannin, oxalate and phytate contents were 260, 185, 388.50, 83.25 and 240.50 mg/100 g DM respectively. Also, the hydrocyanic acid (HCN) and phytohaemaglutinin concentrations were 6.98 mg/kg/DM and 1026 Hu g-1, respectively (Table 3).
| Table 1: | Proximate composition of raw S. obtusifolia seeds |
*Values are means of three replicates, **Value is percentage
of wet weight |
|
| Table 2: | Vitamin composition of raw S. obtusifolia seeds |
| *Values are means of three replicates, ND: Not detected | |
| Table 3: | Anti-nutrient composition of raw S. obtusifolia seeds |
| *Values are means of three replicates | |
| Table 4: | Mineral composition of raw S. obtusifolia seeds |
| *Values are means of three replicates, ND: Not detected | |
The results show that calcium (Ca), potassium (K), phosphorus (P), sodium (Na), magnesium (Mg), iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo), cobalt (Co), chromium (Cr), selenium (Se), sulphur (S) and fluorine (F) contents were 960, 1200, 810, 600, 640, 234.60, 53.12, 10.48, 0.04, 0.38, 0.26, 0.03, 0.03 and 1.34 mg/100 g, respectively (Table 4). Iodine (I) was below the detectable limit. Potassium was the most abundant mineral element while the least value was recorded for S and Se.
The concentration of essential amino acids (EAA) was 4.50, 4.02, 4.39, 7.60, 3.01, 2.21, 1.02, 0.92 and 3.54 mg/100 g protein for phenylalanine (Phe), lysine (Lys), valine (Val), leucine (Leu), isoleucine (Ile), threonine (Thr), methionine (Met), cystine (Cys) and tyrosine (Tyr), respectively (Table 5). The total essential amino acid (TEAA) content was 31.21. This was 45.5% of the total amino acid concentration in 100 g of the protein. The semi-essential amino acid content shows that histidine and arginine were 2.11 and 4.67 g/100 g protein, respectively while the total semi-essential amino acid content was 6.78. This value was 9.88% of the total. The non essential amino acid (NEAA) content of S. obtusifolia shows that Asp, Ser, Glu, Pro, Gly and Ala contents were 8.30, 3.00, 9.16, 2.33, 4.11 and 3.71 g/100 g protein. The total non-essential amino acids (TNEAA) content was 37.39. This was 54.50% of the total amino acid concentration in a 100 g of protein. Among all the amino acids detected, glutamic acid was predominant while cystine was the least abundant.
| Table 5: | Amino acid composition of raw S. obtusifolia seeds |
| *Values are means of three replicates | |
DISCUSSION
The DM value was high. The high dry matter content was similar to values obtained for most raw seeds of legumes like Milletia obanensis, Lablab purpuresus, Phaseolus aureus and Vigna sinensis (Umoren et al., 2005; Osman, 2007; Mubarak, 2005; Khattab et al., 2009). This will reduce the cost of handling and ensure long term storage. The CP content was high. This was higher than the range 15.52-20.74% DM reported for its close relative, Cassia hirsuta (Vadivel and Janardhanan, 2000) and another Nigerian legume, Afzelia africana (Obun and Ayanwale, 2008) but comparable to the value for raw African locust bean (Parkia filicoidea) and Mucuna utilis (Bawa et al., 2007; Tuleun and Patrick, 2007). Differences observed with its close relative could be due to the variety. The high CP value will enhance its replacement value for soybeans. The EE value was low compared to values reported for C. hirsuta (3.77-7.04%), M. utilis, P. filicoidea, M. obanensis and other African bean seeds (Vadivel and Janardhanan, 2000; Bawa et al., 2007; Tuleun and Patrick, 2007; Umoren et al., 2005; Ajah and Madubuike, 1997) and could be attributed to genetic differences as they affect the composition of seeds. Low EE value of foods contributes to poor energy content of such material compared to soybean that is an oil bean seed. The calorific value was lower than 566-580, 426-430, 390-415 and 560-580 kcal/100 g reported for A. africana, Brachystegia eurycoma, Canavalia ensiformis and Pentaclethra macrophylla (Ajah and Madubuike, 1997) and that reported for maize (Aduku, 1993). This could be due to the low EE and NFE values which are the major contributors to the energy value of foods. The low energy value will create a need for the supplementation with high energy sources like palm oil.
The riboflavin and thiamine contents of S. obtusifolia were low compared to 4.24 and 2.75 mg/100 g of Amaranthus hybridus (Akubugwo et al., 2007). This is in line with literature which reports that grains are poor sources of these vitamins but green leafy vegetables, yeast and milk are rich (McDonald et al., 1995). Riboflavin forms the prosthetic part of many enzymes and its deficiency in diets causes marked swelling and softening of sciatic and brachial nerves in chicks (Banerjee, 2004). The niacin content was high compared to A. hybridus leaves. The high niacin content agrees with reports by Vasudevan and Sreekumari (2007) that legumes (pulses) and oil seeds are rich sources of niacin. Also, these authors further stated that niacin supplementation helps to prevent a livestock skin disease called pellagra. Vitamin C content of S. obtusifolia was low. This was lower than 25.40 mg/100 g reported for A. hybridus (Akubugwo et al., 2007). This agrees with Vasudevan and Sreekumari (2007) and Banerjee (2004) who reported that vitamin C is generally poor in seeds but rich in citrus, guava and leafy vegetables. The poor level of vitamin C in diets causes scurvy in animals. The content of vitamin A in S. obtusifolia seeds was low. This was lower than 710 IU/100 g in soybeans but higher than 158 IU/100 g (Vasudevan and Sreekumari, 2007) reported for mung beans (Phaseolus aureus). This agrees with reports by Banerjee (2004) that apart from animal sources, vitamin A source in plants is mainly in fruit and green leafy vegetables while legumes are poor sources. The low level of vitamin A in diets has implication for poor vision, growth and reproductive ability. In an S. obtusifolia rich diet therefore, supplementation should be done with fish oils and green leafy vegetables (Banerjee, 2004).
The alkaloid content was high. Though lower than 2000 mg/100 g in lupin seed meal, it is still above the upper limit of 60 mg/100 g recommended for a safe feed (McDonald et al., 1995). This therefore makes it potentially toxic to livestock especially young ruminants and monogastric fed raw S. obtusifolia seeds in diet. There is need therefore for processing of this pulse.
The saponin value was higher than the recommended value for a safe feed (McDonald et al., 1995). The high value of saponin must have contributed to the high content of the alkaloid saponin is an alkaloid. High values of saponin and other alkaloids in diets rich in this seed will expose the animals to the risk of haemolysis of some blood tissues and injury to the digestive mucosa especially in pigs. Also, high bitter taste and low palatability will be common (McDonald et al., 1995).
The tannin content was high. This was higher than values obtained for M. obanensis (0.44 mg/100 g) Umoren et al. (2005) but comparable to 330 mg/100 g reported for mung beans (Mubarak, 2005). Tannins are known to cause growth depressing effects on non-ruminants. Processing of the seeds before feeding is therefore necessary.
The oxalate value was high compared to 37.5 mg/100 g in M obanensis (Umoren et al., 2005) though lower than 195 mg/100 g reported for M. utilis seed meal (Tuleun and Patrick, 2007). High oxalate content in S. obtusifolia seeds has the potential to cause metabolic calcium deficiency by inhibiting its absorption from the intestine (McDonald et al., 1995).
The phytate level was low compared to 605.39 mg/100 g reported for raw sweet Lablab bean variety (Osman, 2007) and 888.33 mg/100 g recorded for Hibiscus sabdariffa (karkade or rosselle) seeds (Yagoub et al., 2008). However, this was higher than 6.00-14.31 mg/100 g reported for different varieties of Lablab beans (Abeke et al., 2008); 3.98 mg/100 g reported for M. obanensis (Umoren et al., 2005) and 5.0 mg/100 g of raw mung bean seeds (Mubarak, 2005). The high phytate level could render the phosphorus value of the beans unavailable to man and livestock inhibit certain digestive enzymes as well as lowering the availability of other mineral elements like Ca and Mg (McDonald et al., 1995; Siddhuraju et al., 1995; Umoren et al., 2005).
The hydrocyanic or hydrogen cyanide (HCN) content was low. Th is was lower than 2.60 mg/100 g (i.e., 26 mg/kg DM) and 1.79-3.47 mg/100 g (i.e., 17.9-34.7 mg kg-1 DM) reported for M. obanensis (Umoren et al., 2005) and L. purpureus bean (Abeke et al., 2008), respectively.
The concentration of phytohaemaglutinin for S. obtusifolia was low. This was lower than 2670 Hu g-1 reported in raw mung bean seeds (Mubarak, 2005), therefore necessitating no processing to reduce the concentration of these ANFs to an acceptable level.
The high level of some anti-nutritional factors in S. obtusifolia limits its utilization as livestock feed and human food. However, different heat treatments and other processing methods have been found to render these anti-nutrients inactive, improving its value as a feed and food source.
The Ca value was high. This was high compared to 139, 47.4, 582.00 and 84 mg/100 g reported for raw Lathyrus maritimus (beach pea), M. obanensis (odudu) Nigeria Cowpea (Vigna spp.) and mung bean (P. aureus) seeds, respectively (Shahidi et al., 1999; Umoren et al., 2005; Chinma et al., 2008; Mubarak, 2005). Calcium is necessary for teeth and bone formation, blood clothing, the working of muscles, regulation of heartbeat and maintenance of acid base equilibrium in the body of animals and legumes are abundant in it (Banerjee, 2004).
The K level was very high compared to 451, 45.3 and 3.62 mg/100 g recorded for beach pea, odudu and mung bean seeds (Shahidi et al., 1999; Umoren et al., 2005; Mubarak, 2005). This high value of K is not surprising as members of the bean family are rich in K (Vasudevan and Sreekumari, 2007). Potassium is necessary for nerve transmission; maintenance of osmotic pressure and acid base equilibrium; activation of certain enzymes; uptake of certain amino acids as well as carbohydrates; and protein metabolism (Banerjee, 2004).
Phosphorus in the form of phosphate ion is needed for formation of bone and teeth, production of high energy compounds e.g ATP, DNA and RNA formation and activation of enzymes. The P content of S. obtusifolia was in this case high compared to the values reported for most tropical legume seeds (Umoren et al., 2005; Mubarak, 2005; Shahidi et al., 1999; Chinma et al., 2008; Elleuch et al., 2007).
The Na content of S. obtusifolia seeds was above the levels reported for beach pea (Shahidi et al., 1999) and sesame (Sesame indicum) seeds (Elleuch et al., 2007). Feeding livestock feed that is rich in S. obtusifolia has the potential to maintain body fluid pH, support nerve transmission and muscular contraction in livestock (McDonald et al., 1995).
The Mg content was high compared to 128-145, 92.3, 183 and 55.6 mg/100 g reported for Nigerian cowpea, M. obanensis and mung beans (Chinma et al., 2008; Umoren et al., 2005; Mubarak, 2005; Shahidi et al., 1999). This implies that feeding livestock on feed abundant in S. obtusifolia seed meal has the potential to lower the irritability of neuromuscular system and activate enzymes like phosphatases which require ATP (Banerjee, 2004).
Iron content was high compared to 11.5 and 8.4 mg/100 g for soybean and mung beans (Vasudevan and Sreekumari, 2007). This indicates the possibility of this legume if fed to livestock, to improve transport of oxygen to the tissues as well as enzymes of electron transport chain and therefore, useful in feeding pigs to prevent Fe deficiency anaemia (McDonald et al., 1995). The high level of Fe agrees with literature that legumes and seed coats are rich in iron (Vasudevan and Sreekumari, 2007; McDonald et al., 1995).
The Zn content compared to 3.1 mg/100 g reported for raw beach pea seeds was high. This agrees with literature (Vasudevan and Sreekumari, 2007). Zinc is an antioxidant and aids in Cu absorption in some disease conditions. Many enzymes are dependent on Zn for proper functioning.
The concentration of Cu in the seed is higher than that reported for some Nigerian cowpea varieties and beach pea (Chinma et al., 2008; Shahidi et al., 1999) but similar to the value reported for roselle seed (Yagoub et al., 2008). Since, this seed is high in Cu, its inclusion in livestock diets could protect the heart by increasing high density lipoprotein (HDL). It is also a co-factor for vitamin C, necessary for tyrosinase activity and Fe absorption and incorporation into haemoglobin. In cases where the minerals were higher or lower than values reported for other legumes, soil type and genetics could be implicated (McDonald et al., 1995).
The Mo, Co, Cr, Se, S and F values were all low compared to reviewed values. Except S, considering the trace requirement for these minerals in livestock diets, their low level may not be of serious consequence especially when they are rich in soils where the S. obtusifolia plants are grown.
The Phe, Val, Lys, Ile, Met, Cys, Thr and Tyr contents were low but within the range of most legumes compared to the values reported for Karkade seeds, kidney beans, cowpea and many other legumes (Yagoub et al., 2008; Khattab et al., 2009; FAO/WHO 1973, 1990; Siddhuraju et al., 1995; Mubarak, 2005; Yanez-Ruiz et al., 2009). The essential amino acids in this situation need to be supplemented in livestock diets for optimum performance to be ensured when feeding monogastrics with S. obtusifolia seed meal rich diets. The Leu content was high. This was higher than 7.0 g/100 g reported for the Food and Agriculture Organization/World Health Organization (1973) reference protein. The concentration was also comparable to values obtained for most legumes reviewed (Shahidi et al., 1999; Yagoub et al., 2008; Khattab et al., 2009; Siddhuraju et al., 1995). Supplementation with Leu rich sources is therefore not necessary in a diet rich in this seed meal.
This TEAAS was lower than the Food and Agriculture Organization/World Health Organization (1973) reference protein value of 36. This suggests supplementation with other sources especially for monogastric animals for the animals to realize their full potential.
Compared to the Food and Agriculture Organization/World Health Organization (1973) reference protein, the His content was high. This value was similar to that obtained for Egyptian pea, Canadian pea, Egyptian kidney bean, Canadian kidney bean, roselle bean and mung bean (Mubarak, 2005; Khattab et al., 2009; Yagoub et al., 2008). Histidine, a semi essential amino acid, is necessary in food for growing animals. It is also needed for the formation of histamine (Vasudevan and Sreekumari, 2007).
The Arg, Asp, Ser, Glu, Pro, Gly, Ala values were low compared to values reported for most legumes. However, they were within the range common to legume seeds (Dubey et al., 2008; Mubarak, 2005; Siddhuraju et al., 1995; Khattab et al., 2009; Yagoub et al., 2008). The highest and lowest values observed for glutamic acid and cystine respectively agrees with results of many workers (Siddhuraju et al., 1995; Khattab et al., 2009; Mubarak, 2005).
CONCLUSION
The study investigated the nutritional value of S. obtusifolia seeds of plants growing in Obanliku, SE Nigeria, as potential plant protein source in livestock diets. It reveals that S. obtusifolia seeds are rich in crude protein, crude fibre, some minerals (Ca, K, P, Na, Mg, Fe, Zn and Cu), amino acids (leucine, histidine, proline and glycine) but also high in some anti-nutrients (alkaloid, saponin, tannin and oxalate). We conclude that S. obtusifolia seeds have the ability to partially replace soybean as a protein source in livestock diets. However, the processing of these seeds before feeding to livestock will help undermine the anti-nutritional effects of the phytochemicals that are abundant in the raw seed meal.