INTRODUCTION:
Medicinal plants have been identified and used throughout human history. Plants have the ability to synthesize a wide variety of chemical compounds that are used to perform important biological functions, and to defend against predators such as insects, fungi and herbivorous mammals. At least 12,000 such compounds have been isolated so far; a number estimated to be less than 10%[1,2]. Chemical compounds in plants mediate their effect on the human body through processes identical to those already well understood for the chemical compounds in conventional drugs. Thus herbal medicines do not differ greatly from conventional drugs in terms of how they work. This enables herbal medicines to be as effective as conventional medicines, but also gives them the same potential to cause harmful side effects [1,2].
The use of plants as medicines predates written human history. Ethnobotany (the study of traditional human uses of plants) is recognized as an effective way to discover future medicines. In 2001, researchers identified 122 compounds used in modern medicine which were derived from "ethnomedical" plant sources; 80% of these have had an ethnomedical use identical or related to the current use of the active elements of the plant[3]. Many of the pharmaceuticals currently available to physicians have a long history of use as herbal remedies, including aspirin, digitalis, quinine, and opium [4].
The use of herbs to treat disease is almost universal among non-industrialized societies, and is often more affordable than purchasing expensive modern pharmaceuticals. The World Health Organization (WHO) estimates that 80 percent of the populations of some Asian and African countries presently use herbal medicine for some aspect of primary health care. Studies in the United States and Europe have shown that their use is less common in clinical settings, but has become increasingly used in recent years as scientific evidence about the effectiveness of herbal medicine has become more widely available [2].
Research on bioactive compounds in the Annonaceae family is growing rapidly. Acetogenin compounds from Annonaceae type were reported to have toxicity that is effective against insects of several orders such as Lepidoptera, Coleoptera, Homoptera and Diptera [5,6]. Other studies reported that Annonaceae family contains acetogenin that are larvicidal. Acetogenin also acts as an insecticide, acaricide, antiparasitic and bactericidal [7]. One plant in the Annonaceae family that has been assessed of its active compound content is Annona muricata Linn also known as Soursop. This plant can be used as traditional food and as insecticide [8]. All parts of A. muricata (soursop) tree are used in natural medicine in the tropic including the twigs, leaf, root, fruit and seeds [9]. The crushed seeds are used against internal and external parasites, head lice and warms. The twigs and leaves are considered sedative and antispasmodic [10]. A decoction of A. muricata (soursop) leaf is used to kill bed bug and head lice and also to reduce fever. For the latter it can have the same effect taken orally or added to bathing water [11].
MATERIALS AND METHODS:
Sample collection, preparation and preservation:
The seeds samples were harvested from the ripe soursop fruits bought from Relief market, owerri, Imo state. The collected samples (seed) were air-dried properly for three weeks. The dried samples were then milled using an electric blender. The milled samples were sieved into fine powder using a 2mm mesh size sieve.
Sample extraction:
250ml 98% ethanol was added to 100g of the
powdered seed sample. (100 g). They were thoroughly shaken and allowed to stand
for 48 hours at the end of which it was filtered using whatman No.1 filter
paper. The residues were rinsed with ethanol, filtered again and the two
filterates combined for concentration. The filtrates were concentrated to
near-dryness in a water bath at 60
after which the remaining solvent was
allowed to evaporate at room temperature. The crude extracts of seed and stem
thus extracted were stored in properly covered and labeled beakers for
purification.
Purification:
Separation and purification was carried out using column chromatography method. 11g seed crude extracts were respectively weighed into appropriately labeled beakers and dissolved with a little amount of petroleum ether. Silica gel was then added to the extracts, a little at a time and stirred until a free-flowing slurry is achieved. The seed extract and stem extract slurries were then loaded unto different already packed columns and elution is commenced. A three-solvent system (petroleum ether, acetone and methanol) was used in the elution process in mixtures of increasing order of polarity. Fractions were collected in 50ml beakers at a volume interval of 20ml/ fraction and at the end, 24 fractions of the seed extract were collected.
TLC analysis:
All the fractions collected were subjected to TLC analysis to see if there are any pure fraction(s). The plates were coated with silica gel and allowed to dry at room temperature. The fractions from column chromatography were then spotted on the dried silica gel-coated plates using a micro pipette.The Retention factor (Rf) values were calculated thus: Distance travelled by solvent/Distance travelled by sample
GC-MS analysis:
The seed extract (SE10) were sent for chemical analysis using GC-MS in which 10ml of the fraction was transferred into appropriately labeled sample bottle, carefully sealed and sent to National Institute of Chemical Technology (NICT), Zaira, Kaduna state, Nigeria for GC-MS analysis.
RESULTS AND DISCUSSION:
SE10, gave a single spot with Rf value 0.34 in a solvent mixture of 10 % pet. Ether: 80 % acetone: 10 % methanol. Table 1.0 shows the Rf values of seed fractions (SE7, SE10, SE12 , SE13) in petroleum ether, acetone and methanol mixture of 10 % : 80% :10% v/v.
Table 1: Calculated Rf values of some fractions of the seed extract using petroluem ether: acetone: methanol mixture (10:80:10) v/v.
|
Sample type |
Plate/fraction number |
Number of spots observed |
Rf values |
|
Seed |
SE7 |
3 |
0.090, 0.094, 0.097 |
|
Seed |
SE10 |
1 |
0.340 |
|
Seed |
SE12 |
2 |
0.060, 0.065 |
|
Seed |
SE13 |
2 |
0.060, 0.065 |
Figure 1: Gas chromatogram of Annona muricata seed methanol extract
