In West Africa, dietary pattern vary and is influenced by the vegetation belt. For example in the northern parts of Nigeria, cereals dominate, while in the south, legumes, nuts, seeds and starchy roots or tubers are the main food components (Ene-Obong and Carnovalue, 1982). However, processing of the cereals and starch roots into a form of paste and eaten with soups is the general practice. Among the legumes used in soups (mainly for emulsification and stabilization of soups) are Brachystegia eurycoma (achi), Detarium microcapum (ofor), Mucuna pruriens (ukpo) and Irvingia gabonensis (ogbono). Each of the soup thickeners differ in species from the others and so have their individual characteristic flavours, which they impart to soups. Often, choice depends on individuals, but Brachystegia eurycoma and Detarium microcarpum are favourite soup thickeners in South Eastern Nigeria.
Trowell (1975) reported the lowering effect on blood glucose level and blood cholesterol content by dietary fibre; while Pederson et al. (1980) reported that the supplementation of the diets of diabetic patients or those with impaired glucose tolerance with fibre in the form of bran, or guar gum or the use of naturally high fibre foods such as whole grains cereals or dried legumes resulted in an improvement in blood glucose profiles, reduction in urinary glucose and a decrease in the mean serum cholesterol level.
Experiments have shown that hydrocholloids physiologically function as soluble fibre when ingested and as such are very effective in reducing blood cholesterol levels and moderating glucose response in diabetics (Fumiwayo, 1985). Though hydrocholloids are good sources of soluble fibre, they have the ability to imitate and replace fat in processed food and so have been shown to be essential component in low fat and fat free products (Glicksman, 1982). Sources of hydrocholloids are mainly from plant materials. Two of such plants are Brachystegia eurycoma and Detarium microcarpum known locally in the South Eastern part of Nigeria as Achi and Ofor, respectively. Brachystegia eurycoma belongs to the family Caesalpiniaceae, phylum spermatophyte and order fabaceae. It is a dicotyledonous plant, classified as legume and grows commonly along river banks. It flowers between April and May and fruits between September and January. The fruits are very conspicuous and persistently woody. The seed flour of Brachystegia eurycoma have gelation proterties and imparts a gummy texture when used in soups, which is a desirable attribute necessary for the eating of garri, pounded yam, etc.
Detarium microcarpum belongs to the family caesalpiniceae, phylum spermatophyte
and the order fabacea. It is particularly associated with dry savannah countries.
It is known to flower throughout the wet season and fruits between November
and January. The fruits are fleshy and quite edible (Keay et al., 1964).
The bark of Detarium microcarpum has diuretic and anti-inflammatory effects
and reduces blood glucose levels in diabetic patients. The functional properties
are quite similar to those of Brachystegia eurycoma, hence it is equally
classified as a food gum (Fatope et al., 1993).
The presence of phytochemicals alongside nutrients in plant materials is obvious. We thought it necessary to investigate the effect of processing methods on the nutritive and antinutritive properties of seeds of Brachystegia eurycoma and Detarium microcarpum and their probable effects on public health.
MATERIALS AND METHODS
Sample collection and pretreatment: The mature dry seeds of Brachystegia
eurycoma and Detarium microcarpum were bought as sold in Okigwe market;
and graciously identified by Dr. Bob Ezumah of the department of Plant Science
and Biotechnology Abia State University, Uturu, Nigeria. The seeds were sorted
to remove debris and unviable ones and stored in cellophane bags to avoid contamination.
Pre-dehulling treatments: The traditional methods of processing as described by Ene-Obong and Carnovalue, 1982) was adopted in the treatment of both types of seeds. The seeds after sorting were roasted for 10-15 minutes; then soaked immediately for at least 1 hour in cold distilled water after which the cotyledons were soaked overnight in distilled water. The water was drained off and the cotyledons sun-dried and finally ground into fine power. This represents the dehulled sample. The undehulled sample was prepared by simple cleaning the seeds and grinding into fine power without prior roasting or soaking in water.
For the seeds of Detarium microcarpum, they were boiled for 45-60 mins with distilled water and dehulled. The seeds were washed for 3 or 4 times with distilled water and soaked overnight in distilled water. The water was drained off and the seeds sun dried and then milled. The undehulled seeds were equally milled without roasting or soaking.
Proximate analysis: Standard conventional methods were employed in all the analysis. Crude fat was extracted by the soxhlet extraction method with petroleum ether (40-60oC) for 8 hours as described by James (1995). Crude protein content was determined by the micro kjeldahl method. Available carbohydrate, crude fibre, ash and moisture contents were estimated as described by the Association of official analytical chemists (AOAC, 20005).
Determination of mineral content: Calcium, sodium, potassium, magnesium and phosphorus were determined according to the method of Shahidi et al. (1999). The sound seed samples were sieved with a 2mm rubber sieve and 2g each of samples were weighed and subjected to dry ashing in a well-cleaned porcelain crucibles at 550oC, in a muffle furnace. The resultant ash was dissolved in 5ml of HNO3/HCL/H2O (1:2:3) and heated gently on a hot plate until brown fumes disappeared. To the remaining materials in each crucible, 5ml of deionized water was added and heated until a colourless solution was obtained. The mineral solution in each crucible was transferred into 100ml volumetric flask by filtration through a whatman No 42 filter paper and the volume made to the mark with deionized water. This solution was used for elemental analysis by atomic absorption spectrophotometer. A 10cm long cell was used and concentration of each element in the sample was calculated on percentage of dry matter.
Phosphorus content of the digest was determined colorimetrically according to the method described by Nahapetian and Bassiri (1975).
Determiantion of phytochemicals: Alkaloids were determined by the method as described by Higuchi and Hassan (1973). Tannins were determined by the method of Price et al. (1978); Bainbridge et al. (1996), Saponins, flavonoids, glycosides and steroidal aglycon were variously determined by the method of Harbone (1973).
Statistical analysis: Values are expressed as mean±standard error of mean. Significant differences between values are determined using the students T-test. Differences existed at p < 0.05 (Steel and Torie, 1986).
Result on Table 1 shows that both B. eurycoma and D. microcarpum have high content of carbohydrate 56.0±0.00, 52.5±0.01 and 59.0±0.01, 57.0±0.01 for undehulled and dehulled samples, respectively. Crude fat content is also high, 15.0±0.04, 18.5±0.03 and 14.0±0.01, 15.5±0.02 for the undehulled samples of both seeds. Moisture and crude protein content is equally high followed by Ash content. The crude fibre content is low in both seeds 2.9±0.01, 2.0±0.04 and 1.4±0.02, 1.1±0.02, respectively.
The seeds of B. eurycoma shows high content of calcium 0.80±0.30 and 0.72±0.01 for the undehulled and dehulled seeds, respectively as compared with 0.35±0.20, 0.34±0.01 for seed of D. Microcarpum. Magnesium and potassium are next in value 0.21±0.20, 0.16±0.20, 0.24±0.10, 0.21±0.04 and 0.17±0.10, 0.10±0.12, 0.18±0.02, 0.15±0.03 for undehulled and dehulled samples, respectively. The lowest mineral in these seeds is sodium, which has a value of 0.05±0.11, 0.11±0.02 and 0.14±0.10, 0.13±0.03 for undehulled and dehulled seeds of B. eurycoma and D. nicrocarpum, respectively. Phosphorus is present as 0.33±0.10, 0.30±0.25, and 0.18±0.22, 0.15±0.11, respectively.
||Nutritive Composition of B. Eurycoma and D. Microcarpum
(mg/100gm dry weight)
|Results are mean±SD of triplicate determinations.
Results on Table 3 shows that both seeds contain Tannins, Saponins, Flavonoids, Glycosides, Steroidal aglycon and Alkaloids.
Result on Table 1 shows the nutritive composition of B. eurycoma and D. microcarpum. Generally there seems to be a reduction in nutrient values when the seeds are processed; as shown by the difference in values for undehulled and dehulled samples. The protein content of D. microcarpum; (11.4±0.04, 8.2±0.03) for undehulled and dehulled samples is of significantly (p < 0.05) high level than that of B. eurycoma (9.1±0.02, 7.2±0.05) for the undehulled and dehulled samples, respectively. It could be said that in terms of protein contents, seeds of D. microcarpum should be preferred. The functions of protein which include supply of amino acids, body building and replacement of worn-out tissues may be achieved more with D. microcarpum.
Fibre content of B. eurycoma (2.9±0.01, 2.0±0.04) is significantly (P < 0.05) higher than that of D. microcarpum (1.4+0.02, 1.1±0.02). The higher content of crude fibre probably explains the bulky ash content of B. eurycoma (4.5±0.03, 3.5±0.02) as against (2.0±0.01, 1.5±0.01) for D. microcarpum. The difference is quite significant at (P < 0.05). However, both seeds are good source of dietary fibre. This finding is in agreement with that of Ene-Obong and Carnovale (1982) who reported high dietary fibre content 5.13g per 100g dry matter for B. eurycoma and 50g per 100g dry matter for D. microcarpum. Fibre in diet play very significant roles. Certain physiological responses have been associated with the consumption of dietary fibre e.g. increase in faecal bulk, lowering of plasma cholesterol, a blunting of the post-pranal increase in plasma glucose and a lowering of nutrient bioavailability (Ene-Obong and Carnovalue (1982).
The percentage crude fat of D. microcarpum (18.5±0.03, 15.5±0.02 is significantly (P < 0.05) higher when compared with those of B. eurycoma (15.0±0.04, 14.0±0.01). Hence, in terms of fat content the seeds of D. microcarpum may be preferred. The significance of fat in food may not be over-emphasized as it contributes greatly to the energy value of foods. It could also slow down the rate of utilization of carbohydrates. During starvation, fat could be metabolized by the process of beta oxidation to provide energy for the body and provides more energy when compared with carbohydrates. Fat is an important vehicle for fat soluble vitamins and also acts as lubricants in the intestine.
The available carbohydrate (which excludes non-starch polysaccharides which are not digested by the endogenous enzymes of the human upper digestive system) is not significantly (P < 0.05) different in B. eurycoma (56.0±0.00, 59.0±0.01) than in D. microcarpum (52.5±0.01, 57.0±0.01). Though this comparison may differ if the seeds are singly compared, since this assumption is based on the higher bulk density of one D. microcarpum seed to one B. eurycoma seed. The very high carbohydrate content of these seeds as well as their ability to form viscous gums at such low concentrations as 0.1-1% in sauce shows they belong to the class of food ingredients known as hydrocolloids (Ihekoronye and Ngoddy, 1985). Apart from the supply of energy, studies have shown that viscous polysaccharides can slow the rate of gastric emptying (Schwartz et al., 1982). Within the small intestine, viscous polysaccharides which can form gel matrix, may slow absorption by trapping nutrients, digestive enzymes, or bile acids in the gel matrix and by slowing mixing and diffusion in the intestine. Leeds et al. (1999) have shown through animal experiments, that viscosity is necessary for gum to blunt the rise in plasma glucose load. Thus the high carbohydrate content of these seeds is quite significant to health.
The seeds are rich in minerals (Table 2). While B. eurycoma
had (0.80±0.30, 0.72±0.01); D. microcarpum had (0.35±0.20,
0.34±0.01) for the undehulled and dehulled seeds, respectively for calcium.
B. eurycoma had significantly (P < 0.05) higher calcium content compared
to D. microcarpum. Magnesium content is equally high, with B. eurycoma
having (0.21±0.20, 0.16±0.20) and D. microcarpum (0.24±0.10,
0.21±0.04) for the undehulled and dehulled seeds. The difference in magnesium
content is not significant at (P < 0.05) in their content of these minerals;
(0.05±0.11, 0.11±0.02) and 0.14±0.10, 0.13±0.03)
for sodium and (0.17±0.10, 0.10±0.12); (0.18±0.02, 0.15±0.03)
for potassium in B. eurycoma and D. microcarpum, respectively.
B. eurycoma therefore could serve as a good source of calcium which
is necessary for development of strong bones and teeth.
||Mineral Composition of B. Eurycoma And D. Microcarpum
(mg/100g dry weight)
|Results are means±SD of triplicate determinations
||Phytochemical Composition of B. eurycoma and D.
microcarpum (mg/100g dry weight)
|Results are means±SD of triplicate determinations
Normal extra-cellular calcium concentrations are necessary for blood coagulation
and for the integrity of intracellular cement substances (Okaka and Okaka, 2001).
The use of these seeds especially B. eurycoma in the diet of children
could serve as a rapid supplementation of calcium for children with calcium
deficiency. The balance of ions in the tissues is often of importance e.g. normal
ossification demands a proper ratio of calcium to phosphorus, the normal ratio
between potassium and calcium in the extracellular fluids must be maintained
to ensure normal activity to the muscle. Sodium and Potassium are the major
factors in osmotic control of water metabolism.
The phytochemical content (Table 3) of these seeds shows that D. microcarpum has a higher total alkaloid content (1.56±0.11, 1.25±0.33) than B. eurycoma (1.05±0.01, 0.95±0.35) for the undehulled and dehulled seeds respectively. The total alkaloid content of these seeds is not significantly (P < 0.05) different.
The presence of alkaloids in these seeds is of interest. This is because alkaloids have dual functions. At high concentrations most alkaloids are toxic, while having pharmacological effects at low concentrations. Some alkaloids like colchicines and vinca are capable of inhibiting mitotic cell division, phagocytosis as well as having lymphotoxic activity that are dangerous to health even at low concentrations (Higuchi and Brocham, 1973). B. eurycoma contains tannins, with the undehulled seeds having a significantly (P < 0.05) higher content than the dehulled; while D. microcarpum showed no trace of tannin at least at detectable levels. The presence of tannin in B. eurycoma explains the darkening of soups within few days of preparation. Tannin being complex phenolic polymer is capable of enzymatic oxidation, hence the pigmentation or browning of foods that contain tannin as seen in some yam species which browns when cut. Tannins have stringent properties, hasten the healing of wounds and inflamed mucous membranes (Agoha, 1974).
Both seed types contain saponins probably in similar quantity. However, there seems to be little danger with the concentrations of saponins present, as the saponins ingested are destroyed in the gastro intestinal tract, hence very little is absorbed into the system if any. Both seeds have high flavoniod content (1.56±0.20, 1.45±0.30) and 1.82±0.06, 1.58±0.05) which are not significantly (P < 0.05) different. Flavonoids are potent water soluble antioxidants and free radical scavengers, which prevent oxidative cell damage, strong anticancer activity (Del-Rio et al., 1997). In the intestinal, tract flavoniods lower the risk of heart disease, provide anti inflammatory activity (Okwu, 2004).
Generally, the low levels of these phytochemicals most of which are lost during processing, indicate an overall good quality of the two seeds nutritionally.
This study, therefore has provided some biochemical basis for the use of these food thickeners by the people of South-eastern Nigeria. As a rich source of nutrients, minerals and phytochemicals, they could be playing a major role in the nutritional status of this group of people.
The authors acknowledge the extensive literature supplied by Prof. A.I. Ukoha of the department of Biochemistry Federal University of Technology Owerri.