The demand for vegetable oils has ever been widening in Nigeria as industrialists rely mostly on the popular vegetable oils like palm oil, palm kernel oil, groundnut oil and coconut oil for the preparation of their various products (Akintayo, 2004). The increasing demand for vegetable oils and fats in Nigeria, for both domestic and industrial purposes, in recent times, is partly due to the nutritional needs of the teaming population and the increasing number of industries that require oils and fats as their primary raw material. Nigeria however, being a tropical country, has wide variations in climatic conditions and therefore has a wide variety of domestic plants that produce oil. Lack of information on the composition and utilization of the many and varied oil seeds, indigenous to Nigeria is more of a problem than the shortage of these oils. This study is therefore aimed at revealing the potentials of less-known seed oil, Pentaclethra macrophylla oil, which could very well replace the popular vegetable oil.
The African oil bean (Pentaclethra macrophylla) is a native of tropical Africa and belongs to the family Leguminosea. It is popular in Nigeria where it is known by several names such as Apara in Yoruba for the seed as well as the fermented product and the most prominent being Ugba (Igbo), as it is a popular condiment and meat analogue among consuming populations (Enujiugha and Akanbi, 2005).
The tree thrives in the Eastern and Southern parts of Nigeria. It grows to a height of about 21 m up to 6 m in girth and it is well branched, forming crown-like canopy. It flowers between March and April after which the pods (brown and woody when matured) open by explosive mechanism, dispersing the seeds and curls up. The seeds are dorso-ventrally flattered, hard, brown in colour and about 6 cm long and 3 cm wide (Achinewhu et al., 1998).
The mesocarp of P. macrophylla seed serve as food, eaten as snack or dessert (evening meal) or used as condiment. It is prepared by first boiling for about 12 h, dehulled, sliced, wrapped in plantain leaves and allowed to ferment for a period of between 2-4 days at ambient temperatures. It may then be mixed with palm oil, spiced and eaten with cooked cassava chips (African salad) or with roasted yam. P. macrophylla has been reported to be rich in protein (48%), amino acids and fatty acids (Ikediobi, 1981).
In this study, we report the characteristics of African oil bean (Pentaclethra macrophylla benth) seed with a view to ascertaining its industrial potential.
MATERIALS AND METHODS
The seed of P. macrophylla were obtained from Uselu market in Benin
City, Edo State, Nigeria. The seeds were dehalled and powdered by grinding in
a Labmill laboratory machine. Oil was extracted using n-hexane in a soxhlet
apparatus, in batch-wise operation. Solvent was removed in a rotavapour. The
extracted seed meals were thoroughly air-dried to remove traces of solvent.
The extracted seed oils were immediately analyzed for some physicochemical properties
(iodine value, saponification value, peroxide value, free fatty acids, refractive
index) using standard methods (AOAC, 1990).
The free fatty acid was calculated from the relationship given by Norris (1965). The mean molecular mass was estimated from the relationship (56/Saponification value) x 100 (Ajiwe et al., 1995). Proximate analysis of the seeds was carried out as described by the Association of Official Analytical Chemists (AOAC, 1995). Fatty acid composition of the oils was determined as described by Akintayo (1997). The mineral content (Ca, Mg, Fe, Pb, Cu, Mn and P) was obtained through colourimetirc method by using UV-visible technique with a 21D spectrophotometer (430-545 nm).
RESULTS AND DISCUSSION
Proximate analysis: The moisture content of P. macrophylla is
fairly high and this could imply short self life. The value compared favourably
with those of other seed oils e.g., Melon seed and Desterium microcapum
(Tallow) seed oils (Eromosele, 1993). The crude fibre and ash content values
are important in terms of the suitability of the seed cakes for the compounding
of animal feeds. As a result of the low crude fibre content, the African oil
bean seed may be considered unsuitable for compounding animal feeds. However,
on the grounds of high carbohydrate content and low ash content, it may be considered
otherwise (Abighor et al., 1997). The protein content of the seed was
fairly low. The high oil content (47.90%) implied that processing the seeds
for oil would be economical (Table 1). The value also compared
favourably with that obtained for Jatropha curcas (47.25%) (Akintayo,
Characteristics of the oil: The oil was light brown in colour. The iodine
value of the oil shows that it is non-drying oil. This makes it unsuitable for
varnishes, polish and alkyd resins. The high saponification value of the oil
implies that it consists primarily of high molecular weight fatty acid glycerides.
This also indicates its suitability in the production of soaps and shampoos.
Generally, this high saponificaiton value and low unsaponifiable matter in the
oil suggest that it is a normal triglyceride (Table 2).
The free fatty acid obtained in this analysis compares favourably with those
reported for some conventional oil seeds such a soybean, olive and sunflower
oils. Free fatty acid can stimulate oxidative deterioration of oils by enzymatic
and/or chemical oxidation to form off-flavour component.
||Proximate composition (%) of the African oil bean seed flour
||Physico-chemical characteristics of Africa oil bean seed
||Minerals composition of the Africa oil bean seeds
The free fatty acid and acid value of P. macrophylla are low and this
suggests its application as a good edible oil. Free fatty acid is also related
to smoke point. P. macrophylla with low fee fatty acid will have a high
smoke point, so it would be suitable for stir-fry cooking. The refractive index
obtained compared favourably with that obtained for Jatropha curcas and
Parkia biglobbossa oils (Akintayo and Bayer, 2002).
Elemental analysis: Calcium (Ca) had the highest concentration of 8.16
μg g¯1. Magnesium (Mg), iron (Fe), lead (Pb) and manganese
(Mn) also showed reasonably high concentrations (Table 3).
The minerals (calcium, magnesium and phosphorus) are micro-elements essential to health. Their presence in the African oil bean seed makes the oil serves as a viable source of these minerals in the body. Also, phosphorus (P) and copper (Cu) levels obtained from the oil analysis were considerably low. Generally, the varying levels of these mineral elements may be due to the different rates at which the elements are taken up from the soil by the plants and subsequent incorporation into the oil.
Evaluation of the composition and characteristics of African oil bean seed (P. macrophylla) shows that the oil has some domestic and industrial potentials.